Radiolarian biogeography in surface sediments of the western Indian Ocean

Marine Mic ropaleon tology, 5 ( 1980): l 11--152 © Elsevier Scientific Publishing Company, Amsterdam --- Printed in The Netherlands

111

RADIOLARIAN BIOGEOGRAPHY IN SURFACE SEDIMENTS OF THE WESTERN INDIAN OCEAN 1

DAVID A. JOHNSON and CATHERINE NIGRINI Woods Hole Oceanographic Institution, Woods Hole, Mass 02543 (U.S.A.) 510 Papyrus Drive, La Habra Heights, Calif. 90631 (U.S.A.)

(Revised version received and accepted September 18, 1979)

Abstract Johnson, D.A. and Nigrini, C., 1980. Radiolarian biogeography in surface sediments of the western Indian Ocean. Mar. Micropaleontol., 5: 111--152. Recurrent group analysis of Radiolaria in 46 core top samples from a north--south transect in the western Indian Ocean has allowed the discrimination of eight distinctive radiolarian assemblages. Most of the designated assemblages have distribution patterns which closely reflect the major oceanographic fronts and first-order patterns of surface water circulation including the South Equatorial Divergence, Subtropical Gyre, Subtropical Convergence, and Antarctic Convergence. An exotic assemblage consisting of four taxa was found off the Arabian coast. These same taxa were previously reported only in the eastern equatorial Pacific, and may be representative of upwelling with relatively restrictive salinities. Radiolarian abundance drops abruptly near 48°S at the Antarctic Convergence, south of which the sediment is a radiolarian-poor diatomaceous ooze.

Introduction Biogenic silica is k n o w n t o be an i m p o r t a n t constituent of the sediments of the Indian O c e a n , ranging in l a t i t u d i n a l e x t e n t f r o m t h e Antarctic continental margin to the southern m a r g i n o f Asia (Lisitzin, 1 9 6 7 , 1 9 7 2 ; Lisitzin et al., 1 9 6 7 ; Jous6, 1 9 7 7 ; Caulet, 1 9 7 7 , 1978). T o date, h o w e v e r , t h e r e h a v e b e e n relatively f e w a t t e m p t s t o i n t e r p r e t spatial v a r i a t i o n s in siliceous m i c r o f o s s i l a s s e m b l a g e s o f t h e I n d i a n O c e a n in t e r m s o f t h e f i r s t - o r d e r o c e a n o g r a p h ic p r o p e r t i e s o f s u r f a c e a n d s u b s u r f a c e waters. Among the previous reports on radiolarian d i s t r i b u t i o n p a t t e r n s in t h e I n d i a n O c e a n surface s e d i m e n t samples, t h o s e o f Nigrini 1 Contrib, No. 4441 of the Woods Hole Oceanogr. Inst.

{1967), P e t r u s h e v s k a y a ( 1 9 6 7 , 1 9 7 1 , 1 9 7 2 a , b, 1973), Lozano and Hays (1976) and Dow ( 1 9 7 8 ) are especially n o t e w o r t h y . Nigrini ( 1 9 6 7 ) i d e n t i f i e d a n d c o u n t e d 45 species o f R a d i o l a r i a in 32 s u r f a c e s e d i m e n t s a m p l e s w h i c h s p a n n e d t h e entire I n d i a n O c e a n a n d e x t e n d e d t o 45°S. She was able t o d i s c r i m i n a t e a l o w - l a t i t u d e assemblage, c o m p o s e d o f twelve t a x a a n d e x t e n d i n g f r o m 10°N t o 20°S; a n d a m i d d l e - l a t i t u d e assemblage, c o m p o s e d o f seven t a x a a n d e x t e n d i n g f r o m 35°S t o 45°S. Nigrini suggested t h a t t h e s e t w o regions are s e p a r a t e d b y t h e core o f t h e subt r o p i c a l a n t i c y c l o n i c gyre, w h i c h is essentially b a r r e n o f radiolarians. Petrushevskaya (1967, 1971) examined r a d i o l a r i a n assemblages in a p p r o x i m a t e l y 70 core t o p s a m p l e s o b t a i n e d on t h e Soviet Ant-

112 arctic Expedition (1955--1958). Sample coverage extended from the Bay of Bengal to the Antarctic continental shelf, but the majority of the samples were from south of the Subtropical Convergence near 40°S (Petrushevskaya, 1967, fig. 4). From observations of the distribution patterns of approximately 75 taxa, she was able to discriminate five principal zoogeographical groups of Radiolaria: (1) A tropical group, confined to latitudes north of the Subtropical Convergence (near 40°S). (2) A subtropical group, found n o t only in the tropical region b u t also extending southward into the " n o t a l " zone between the Subtropical Convergence and the Antarctic Convergence or Antarctic Polar Front (near 50°S). (3) A cosmopolitan group, widely distributed in tropical, temperate, and high-latitude regions of all oceans. (4) A group restricted to Antarctic regions, south of the Antarctic Convergence, Petrushevskaya (1971) further subdivided this group into "high-antarctic species", which are relatively more abundant south of 60°S; and "low-antarctic species", which are most abundant near 60°S and become relatively rare near the Antarctic continent. (5) A bipolar group, which occurs in the North Atlantic boreal zone as well as in middle to high latitudes of the southern Indian Ocean. Petrushevskaya ( 1971) suggested that only two of these groups (the "tropical group" and the "high-antarctic group") can be used as indicators of specific water masses. She also pointed o u t that radiolarian preservation is usually good to excellent in all regions except the " n o t a l " zone, where shell preservation is usually very poor. Lozano and Hays (1976) examined core top samples from the South Atlantic and western Indian Ocean sectors of the Antarctic Ocean (east of 80°E: south of 35°S). Using Q-mode factor analysis (Imbrie and Kipp, 1971) on 72 samples which they considered to represent non-reworked Recent sediments,

they were able to resolve three factors or assemblages (Antarctic, subantarctic and subtropical) with distributions closely corresponding to the principal surface water masses in the area. Dow {1978) carried o u t similar procedures on 36 core top samples from the southeastern Indian Ocean between 40°S and 65°S. After counting 52 radiolarian species or species groups in each sample, 35 of the species were grouped by Q-mode factor analysis into four distinct factors or assemblages. One of these assemblages (the "Antarctic Factor") was found to characterize the region south of the Antarctic Polar Front; a second assemblage ( t h e " Su bantarctic Factor") was dominant in northern samples close to the Subtropical Convergence; and a third assemblage (the "Transitional Factor") reached its highest abundance in the intermediate region near the Antarctic Polar Front. A fourth assemblage was found to be indicative of lateral advection by b o t t o m water activity. Dow (1978) was able to formulate regression equations which related the distribution of the first three factors to summer and winter values of sea-surface temperature. During the decade since the initial studies of Nigrini (1967) and Petrushevskaya {1967), the number of available cores from the Indian Ocean north of the Antarctic Convergence has increased enormously. There are now well over 300 piston and gravity cores from the Indian Ocean (north of 50°S) in the collections of Lamont-Doherty, Scripps, and Woods Hole. Moreover, the extensive studies of Holocene radiolarian biogeography by CLIMAP workers (e.g., Sachs, 1973a, b; Moore, 1973; Lozano, 1974; Robertson, 1975; Molina-Cruz, 1977; Morley, 1977; Moore, 1978) and by others (e.g. Petrushevskaya, 1967; Nigrini, 1967, 1968, 1970; Goll and Bj~brklund, 1971, 1974) have allowed Nigrini and Moore (1979) to synthesize the t a x o n o m y and s y n o n y m y of those extant Radiolaria which have c o m m o n l y been used for biogeographic studies. This updated taxonomic "encyclopedia" has served as a basis for identifying the radiolarian taxa whose

113 geographic distribution patterns were analyzed in the present study. In addition, several compilations and syntheses of extensive oceanographic data collected during the International Indian Ocean Expedition have been completed during recent years (e.g., Wyrtki, 1971; Zeitzschel, 1973). Thus, the geographic distribution patterns and seasonal variability of the major oceanographic parameters have become relatively well identified, and there is, therefore, an increased potential for interpreting microfossil distribution patterns in terms of properties of surface and subsurface waters. The objective of our investigation was to select a longitudinal transect of core top samples in the western Indian Ocean, extending from the Arabian Sea to the Antarctic Convergence near 50°S, to identify radiolarian assemblage distribution patterns, and to interpret their significance in terms of known oceanographic parameters. We selected a western transect in order to avoid the relatively unproductive core of the anticyclonic subtropical gyre, and selected a southern limit near 50°S, south of which extensive studies of radiolarian biogeography have already been carried out (e.g., Hays, 1965; Petrushevskaya, 1967; Lozano and Hays, 1976). In this report we consider only the distribution patterns of Radiolaria in surface sediment samples, and their possible oceanographic significance. Subsequent reports will treat (1) biogeographic distribution pattern of Radiolaria in the eastern Indian Ocean; and (2) paleo-oceanographic interpretation of the late Pleistocene record, using precisely dated core material (Johnson and Nigrini, in prep.). Oceanographic setting of western Indian Ocean With the recent compilation of extensive oceanographic data collected during the International Indian Ocean Expedition (Wyrtki, 1971), the geographic distribution and seasonal variability of the major oceanographic parameters and water masses have become reasonably well identified. The surface cur-

30°E

40 °

50 °

60 °

70'

80°E

Fig. 1. Bathymetric and oceanographic setting of the western Indian Ocean, modified after Defant (1961) and Wyrtki (1973). Bathymetric contours are in kilometers. Heavy arrows designate principal surface currents during the northeast monsoon; open arrows indicate the principal pathway of the deep western boundary current (Warren, 1974, 1978; Johnson and Damuth, 1979). Major frontal zones shown include the South Equatorial Divergence, Subtropical Convergence, and Antarctic Convergence. rents of the Indian Ocean can conveniently be discussed in terms of three major circulation systems (see Fig. 1) and the subsurface distribution patterns of nutrients (Wyrtki, 1973): A. The m o n s o o n gyre

This circulation system is marked by high nutrient values in surface and subsurface waters, with a sharp hydrochemical front near

114 10°S marking the southern boundary of the gyre. During the NE monsoon {November to April), surface water flow north of the equator is from east to west. Off the coast of Somalia most of the water turns south, crosses the equator, and forms the equatorial countercurrent which extends south to near 10°S. The circulation during the NE monsoon is only moderately developed, with no striking upwelling zones. During the SW monsoon (May to October) water flows eastward everywhere north of the equator, and the countercurrent shifts north to join the eastward-flowing monsoon current. Strong upwelling develops along the coast of Somalia between 5°N and l l ° N (Swallow and Bruce, 1966; Warren et al., 1966), and is terminated at the north by a flow of warm surface water out of the Gulf of Aden, forming a strong temperature front (Wyrtki, 1973). Intense upwelling also develops off the coast of Arabia during the SW monsoon. This upwelling is different from the Somali upwelling in that no strong current develops parallel to the coast. However, in volume it may be even stronger than the Somali upwelling region, showing m a x i m u m values of (PO4) -3 in excess of 1,5 ugm-atoms per liter, and a larger area affected by higher concentrations of (PO4) -3 and (NO.~)-' (Wyrtki, 1973, p. 22). High-salinity surface water is formed by the strong excess of evaporation over precipitation in the central and northern Arabian Sea. Two other sources of high-salinity water, the outflow from the Persian Gulf and from the Red Sea, contribute to the formation of a thick layer extending between 150 and 900 m which is of almost uniform salinity. Tongues of water from this layer, which Wyrtki (1973) refers to as the North Indian high-salinity intermediate water, can be recognized hundreds of kilometers " d o w n s t r e a m " from the Arabian Sea source area in several branches of the monsoon current system. Of particular interest for studies of faunal biogeography are the anomalously high values of salinity and nutrients in the Arabian Sea, particularly near the coast of Arabia during

the SW monsoon. B~ and Hutson {1977) recently reported that the northern Indian Ocean is apparently a refuge for relict species of foraminifera (Globoquadrina hexagona, G. conglomerata, and Globigerinella adamsi) which disappeared from the Atlantic during the Pleistocene. These authors suggest (p. 380) that this region "deserves special attention of zoogeographers and paleoecologists, because these relict species may reflect unique ancient oceanic environments". Our work on radiolarian biogeography (this report) documents in the existence of an equally unique radiolarian assemblage in the Arabian Sea, and indicates that the special oceanographic conditions in the area do indeed deserve special attenti on. Thp monsoon gyre is separated from the subtropical gyre by a strong hydrochemical front near 10°S. The front is marked by a salinity minimum in the surface waters extending from Sumatra to Africa, and caused by the advection of low-salinity waters by the South Equatorial Current from the Australian/ Indonesian region. The front is also marked by sharp horizontal gradients in the distribution of chemical properties, particularly oxygen, phosphate, and silica. The front is inclined and slopes from about 100 m depth at 10--12°S to 800 m depth at 16 18°S (Wyrtki, 1973, p. 24).

B. The subtropical gyre This anticyclonic circulation system consists of the South Equatorial Current, the Agulhas Current, and the portions of the west wind drift lying north of the Subtropical Convergence near 40°S (see Fig. 1). There is no strong eastern boundary current off Australia; instead, slow equatorward flow extends across much of the width of the ocean. The South Equatorial Current, drawing water both from the Timor Sea and from the equatorial countercurrent, flows westward toward the northern tip of Madagascar where it divides, with approximately one-third of the water in the current turning south. The Agulhas Current system off southeast Africa is fed by t h e

115

South Equatorial Current, both from the Madagascar Channel and from flow around the southern tip of Madagascar. When the Agulhas Current reaches the longitude of Cape Agulhas, the current turns south and then east to form an elongated eddy which is permanently situated approximately 300 km offshore from southeast Africa. The Subtropical Convergence extends eastward from the Agulhas eddy in a zonal strip between 40°S and 41°S, and separates warm subtropical water of high salinity from cooler temperate water of lower salinity. The Subtropical Convergence is narrower and more sharply defined in the western Indian Ocean (west of approximately 65°E) than in the eastern Indian Ocean (Prell et al., 1979). It coincides approximately with the northern limit of strong westerly winds, which approximates the northern boundary of the Circumpolar Current.

Indian Ocean is an important factor in controlling microfossil preservation, and is a potentially complicating factor producing post-depositional lateral advection of skeletal material " d o w n s t r e a m " from its initial accumulation site. Abyssal flow is well developed in the form of a deep western boundary current (DWBC) in the Crozet, Madagascar, and Mascarene Basins (Fig. 1). This current, consisting largely of Antarctic B o t t o m Water formed in the Weddell Sea, is denoted by eastward-dipping contours of potential temperature and dissolved oxygen along the western margins of the basins (Warren, 1974; Jacobs and Georgi, 1977), and by T-S characteristics which are traceable from basin to basin (Warren, 1974, 1978). From the known path of the DWBC (Fig. 1), selection of samples in the western Indian Ocean transect was carried out so as to minimize the number of samples obtained from regions of DWBC activity.

C. Circumpolar flow Material studied Between a b o u t 40 and 50°S the temperature and salinity decreases from greater than 15°S and 35% 0 to less than 5°C and 34% 0, indicating the surfacing of the main thermocline. This inclined front is associated with intense geostrophic flow in the eastwardflowing Antarctic Circumpolar Current, and is kept in position by strong west winds over the whole area. Cold, low-salinity surface water from Antarctica drifts north under the prevailing westerly winds, where it meets the warmer waters of higher salinity at the Antarctic Polar Front or Antarctic Convergence (see Fig. 1). Mixing along the front forms Antarctic Intermediate Water, which spreads northward as a subsurface salinity minimum. The front is near 48°S in the western Indian Ocean, and appears to undergo little seasonal fluctuation. The s o u t h e m boundary of Circumpolar Flow is the Antarctic Divergence near 65°S, south of which there is a slow westward flow along the Antarctic continental margin. The abyssal circulation of the western

Fifty-three samples from the tops of gravity, piston, and pilot (trigger) cores were prepared from a transect of stations in the western Indian Ocean, extending from the Arabian Sea to south of the Antarctic Polar Front (Table I, Fig. 2). The transect was selected so as to avoid regions of high terrigenous sediment supply, rugged topography (e.g., fracture zones and spreading centers), and possible complications of lateral advection in the deep western boundary current. All cores were examined and sampled by the senior author. Gravity and trigger weight cores were used wherever possible. Smear slides were prepared and examined for the presence of reworked Tertiary discoasters. In some instances (e.g., samples nos. 27, 37, 40, 41; see Table I) the uppermost core material available was several centimeters below the top of the core liner. For these samples we have assumed that the sampled material does in fact represent the uppermost sediment recovered, and that settling or shrinkage of

116

mClla

~, P,'~

A/ JIX X "/~X5 2

Arabia

"~,%.J'~

X5 I

~

Africa ' ./

1

( 78Xx / IOX X9

//

IT X !2x

,/

15X 15x j'.~

xl6

17x

18x

f~-,~S ~ lgX 20x (~]" 22x x25 / -o¢'°~/24X ~ ~' 25X

G / t.~,J

2iX 26~' 28 x x30 33X

27× 29×32x 3,x

35x X3~X~ X x38 36 37 39X 40X

42 K

Regional distribution o f taxa

X4I

43X 45X

47×

i

46 :x

and examined, we eliminated from consideration those south of 50°S, since diatoms outnumber radiolarians by several orders of magnitude in this region. Moreover, Radiolaria from south o f the Polar Front have been studied by previous workers (e.g., Hays, 1965; Petrushevskaya, 1967; Riedel, 1958). We also eliminated 5 samples from the Mascarene Basin in which radiolarian preservation was especially poor, leaving us with 46 samples in the transect (Table I, Fig. 2). One or two specimens of older Radiolaria were observed in a few of the radiolarian samples (Table I); otherwise there is no evidence for significant reworking in any of the material examined.

~,,

48X 49X 50 x §Ix

Fig. 2. Locations of 51 s a m p l e s e x a m i n e d in w e s t e r n I n d i a n O c e a n t r a n s e c t . L o g i s t i c a l i n f o r m a t i o n for e a c h c o r e is given in T a b l e I. T w o a d d i t i o n a l s a m p l e s

examined from south of 50°S had insufficient numbers of Radiolaria for inclusion in the study (Table I).

the sediment has occurred within the core liner since the cores were split, thereby producing the void interval at the top of the liner. Radiolarian assemblages were separated from each sample, using standard procedures described by Riedel and Sanfilippo (1977). In most cases two microscope slides of prepared material yielded a sufficient n u m b e r of Radiolaria for examination, although in several instances additional sample material and/or cleaning procedures were required. From the initial group of 53 samples prepared

The presence or absence of 74 taxa (37 SpumeUaria and 37 Nassellaria) was recorded in each of the 46 samples selected from the transect. No estimates of abundance or counts of total assemblages were made. We believe that presence--absence data alone are sufficient to delineate major water masses , and recent quantitative work by Sancetta (1978) documents that this is indeed the case for three of the four major microfossil groups (including Radiolaria) in North Pacific sediments. Species were chosen for inclusion in the study if they satisfied at least one of the following conditions: (1) known to have some latitudinal restrictions on their distribution; (2) relatively c o m m o n ; and (3) easily recognizable. Most of the species used have been previously described, b u t a few required new or expanded descriptions (see Appendix). All 74 taxa are illustrated in Plates I through V. In the following section, we discuss the distribution pattern of each taxon in the western Indian Ocean transect (see Figs. 3 through 15). Taxa are arranged according to the family level t a x o n o m y of Riedel (1967).

Acrosphaera [lammabunda (ttaeckel) (Fig. 3a; Plate I, 1). Present in most samples north of

117

TABLE I List o f samples used in b i o g e o g r a p h i c s t u d y Sample No.

Cruise

Core No.

Level (cm)

Latitude

Longitude

Water depth (m)

Rad abund,

Rad pres.

1 2

RC 9 AII 15 AII 15 AII 15 RC9 V 14 AII 15 AII 15 CHN 100 CHN 100 CHN 100 ANTP LSD-H DODO AII 93 ANTP AII 93 DODO AII 93 DODO DODO CHN 43 DODO AII 15 V 18 DODO LSD-A DODO V 14 RC 17 V 29 LSD-A RC 17 V 20 RC 14 RC 11 LSD-A DODO RC 14 LSD-A DODO AII 15 LSD-A RC 11 RC 14 LSD-A RC 11 RC 11 RC 11 RC 11 RC 17 RC 17 RC 17

161-TW 596-FF 597-FFA 602-FF 160-P 103-P 8-PG 14-PG 26-PG 29-PG 40-PG 150-G 12-G 173-G ll-PC 142-PG 5-PC 121-PG 4-PC 163-G 157-G 16-PG ll7-PG 735-HC 199-P 151-G 119-G 149-V 86-TW 93-P 53-TW 120-G(b) 91-P 184-TW 17-TW 109-TW 121-G 130-G 16-TW 122-G 132-PG 766-HC 125-G 116-P 13-TW 126-G 104-TW 102-TW 100-P 99-P 62-TW 61-P 52-P

top top top top top top top top top top top 0--3 0-5 5--7 top 0-5 top 4--5 top 5--7 5--7 top 3--5 top top 5--7 13--14 top 5 cm top top top top 5 cm top top 9--10 3--5 top 10--12 8--10 top top top top top top top top top top top top

19°34'N 18°56'N 17°26'N 14°56'N 12°03'N 11°26'N 10°15'N 09°02'N 07°48'N 06°53'N 01°37'N 01°43'S 05 ° 23'S 08 ° 19'S 09 ° 28'S 10 ° 17'S ll°01'S 12° 16'S 15 ° 17'S 15 ° 18'S 17°40'S 18°04'S 18°21'S 20°02'S 20°31'S 21°14'S 22°02'S 22°28'S 23°40'S 23°41'S 24° 16'S 24°30'S 25°21'S 25°48'S 25°49'S 26°36'S 26°51'S 26°56'S 29°05'S 29°54'S 31°02'S 32°00'S 33°14'S 34°55'S 37°23'S 39°46'S 40°55'S 43°42'S 44°50'S 46°31'S 47°35'S 52°12'S 56°22'S

59°36'E 61°23'E 57° l l ' E 57°21'E 63°09'E 56°14'E 53° 10'E 53°40'E 56°12'E 43°41'E 59°40'E 57°32'E 60°02'E 69°01'E 52°10'E 58°58'E 54°32'E 62°50'E 53°31'E 63°42'E 63°23'E 58°24'E 62°04'E 52°29'E 61°55'E 69°26'E 57°33'E 68°03'E 53°09'E 69°41'E 61°54'E 57°29'E 69° 29'E 53°41'E 52° 16'E 56°43'E 58°14'E 61°49'E 52°48'E 61°53'E 64°52'E 55°07'E 61°43'E 67°35'E 59°19'E 64°00'E 57°39'E 58°48'E 60°52'E 61°02'E 57°52'E 54°27'E 51°58'E

3332 3694 1805 3357 4268 4232 4173 4852 4680 5106 5426 4456 4100 3977 4154 2763 4599 3990 4641 3301 3196 3869 3398 4936 3299 3103 4770 3141 4687 2665 4973 4990 3444 5031 5013 5075 5335 4700 4819 4400 4805 4417 4800 4548 5128 4980 4885 4709 4742 4449 4426 3947 5379

C C F A A A A A A A A A A A A A A A A A A A A A C C A C R C A A A R F R -A R A C A A F A A A A A A F ---

G G G G G G G G G G G G G G G G G G G G G M G G G G G G P G M G G P P P -G P G G G G G G G G G G G G ---

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53

Remarks ÷

1 1

1

1

1

2

1 2 2 2 2

D D, 2 D, 2

÷Remarks: 1 = rare r e w o r k e d radiolarian species p r e s e n t ; 2 = i n s u f f i c i e n t radiolaria p r e s e n t for biogeograpbic censu, D = m o s t l y d i a t o m s and s p o n g e spicules.

118

' y ~

India i

l~.\

~

)

t
#

1

;

!

•

Africa

•

•

•

•

•

•

~0"

r

'o"

o ~ • •

*

•

• * **

•

]

•

O O

O*

II

/

j,,%

o O

(

//

•

~o°

rr q ,:>u

) %

,.} •0

t

•

]

,

) • Africa /" /

•

I

'~

r

•

I nd ia


~0TM

•

•

00 •

200

¢

}

•

*

30"

•

-.

..

!

•

~o"

•

°

:,!

"

O 0

o

40"S

~

4o,s I1r

0 0

LAPPACEA

e

Ca)

o

o

50"E

'

(b)

~.)°

"-"'

~

"

o

50"[

6O~

' '-,<~!,.~i~

~

l

•

5o°[

60'

:' ,o

"~ [

"~

:

<....... 7 d; Africa ,/ i /'/

o

°

Arabia

~ O L "k io",~i kj i

\,.~

O0

Africa // @

/f/

/'~" J '

0

u !

0 o

©

o ©

I

• O

,

•

I°°

O

O

o

~

m, I

0 o

©

0

20"

0 0

*

•

•

0

0•

0

O*

0

o

0

0

0

* *

0

eO *

0

0 ©

30"

O

~0"

co

0

0 I I~/AGIItlII"A

,

?'

,_~

1

(e)

50%

o

0 0 6O°

(f)

500E

0

i 40% i i

0

COLLO6PHAERA HUXLEY I

!

r 0

0

2o~ ]

0

0

40%

2,~ 0

0

I ~l

<)

0 0 0

0

0

O

0

]

0

0

*

i

0

c,

0

0 * *

(d)

0 o

0 0

~0 0

io"

•

o

~ *

0 o

•

I

,I India 7o%

m°N

"\\,

",\9 ~

•

o

R jl

L

O0

4) °

ACRC~PHAERA SPINOSA

• •

(c)

?o"

~o o Arabia

•

e

ACI~O6R~ERA

0 0 6O•

COLLOSR~RA I SP. AFF. C. t.IJXLEY I 7o~ j

119 about 33°S; very rare or absent in Arabian Sea samples.

Acrosphaera lappacea (Haeckel) (Fig. 3b; Plate I, 2). Present in most samples north of about 33°S, scattered occurrences between 33°S and 46°S; more a b u n d a n t in low latitudes.

Acrosphaera spinosa (Haeckel) (Fig. 3c; Plate I, 3). Present in all samples except southernmost (about 48°S) and n o r t h e r n m o s t (about 19°N); particularly a b u n d a n t at about 20°S.

Disolenia quadrata (Ehrenberg) (Fig. 4c; Plate I, 9). Present in most samples north of about 22°S, but rare or absent near the Arabian coast; increasingly rare towards the southern extremity of its geographic range.

Disolenia zanguebarica (Ehrenberg) (Fig. 4d; Plate I, 10). Present, except near the Arabian coast, in samples north of about 35°S; increasingly rare towards the southern extremity of its geographic range.

Plate I, 4). Consistently present, but rather rare, in samples north of about 18°S.

Otosphaera auriculata Haeckel (Fig. 4e; Plate I, 11). Consistently present in samples north of about 25°S; increasingly rare towards the southern extremity of its geographic range.

Collosphaera huxleyi Muller (Fig. 3e; Plate I,

Siphonosphaera

Buccinosphaera

invaginata Haeckel (Fig. 3d;

5; Plate IV, 13). Present in most samples between about 18°S and 37°S; see Appendix.

Collosphaera sp. aff. C. huxleyi Muller (Fig. 3f; Plate 1,6; Plate IV, 14). Consistently present in samples north of about 5°N; scattered occurrences of small, impoverished forms between 0 ° and 10°S; see Appendix.

polysiphonia Haeckel (Fig. 4f; Plate I, 12). Present in most samples; absent from sample at 48°S; very rare or absent near the Arabian coast; most abundant in low latitudes. Actinomma antarcticum (Haeckel) (Fig. 5a; Plate I, 13). Present in four samples between about 40°S and 46°S.

Collosphaera macropora Popofsky (Fig. 4a;

Actinomma arcadophorum Haeckel (Fig. 5b;

Plate I, 7; Plate IV, 15). Present in most samples between about 5°S and 20°S with very rare occurrences extending its geographic range to about 10°N and 25°S; see Appendix.

Plate I, 14). Present in most samples north of about 30°S.

Collosphaera tuberosa Haeckel (Fig. 4b; Plate I, 8). Consistently present in samples north of about 25°S.

Actinomma medianum Nigrini (Fig. 5c; Plate I, 15). Bimodal distribution, very rare in samples between about 5°N and 10°S (about 15°S in the western part of the study area), more a b u n d a n t in samples between about 30°S and 46°S.

Fig. 3. Distribution patterns of radiolarian taxa. Open circles represent samples in which the taxon was sought but not found after examination of two or more strewn slides. Half-filled circles represent samples in which only one specimen or questionable fragments of a given taxon were observed. Filled circles represent samples in which two or more clearly identified specimens of the taxon were observed. Asterisks designate five samples in which severe corrosion of the radiolarian skeletons yielded very poor preservation and insufficient skeletal material to reliably determine the presence or absence of a given taxon. In Figs. 3 through 15, maps showing the distribution patterns of the 74 taxa in this study are presented in the same order as that listed in the text, under "Regional distribution of taxa".

120

PLATE

I

121

Anomalacantha dentata (Mast) (Fig. 5, d; Plate I, 16). Bimodal distribution north of about 12°S and between about 30°S and 45°S.

Styptosphaera ? spumacea Haeckel (Fig. 6e; Plate II, 1). Present in all samples between about 37°S and 46°S.

Omrnatartus tetrathalamus tetrathalamus (Haeckel) (Fig. 5e; Plate I, 17). Present in all samples except southernmost (about 48°S); abundant in low latitudes but very rare between about 37°S and 46°S.

Heliodiscus asteriscus Haeckel (Fig. 6f; Plate II, 2). Present in all samples except southernmost (about 48°S).

Cypassis irregularis Nigrini (Fig. 5f; Plate I, 18). Present in four samples near the Arabian coast; very rare. Saturnalis circularis Haeckel (Fig. 6a; Plate I, 19). Bimodal distribution, north of about 15°S and between about 30°S and 46°S; very rare, but distinctive, Spongurus cf. elliptica (Ehrenberg) (Fig. 6b, Plate I, 20). Present in most samples north of about 30°S. Spongurus pylomaticus Riedel (Fig. 6c; Plate I, 21). Present in most samples between about 37°S and 46°S. Spongocore puella Haeckel (Fig. 6d; Plate I, 22). Present in most samples except southernmost (about 48°S) and three samples between about 30°S and 23°S in the eastern part of the study area.

Heliodiscus echiniscus Haeckel (Fig. 7a; Plate II, 3). Present in samples north of about 20°S in the eastern part of the study area, but ranges as far south as 25°S in the western part. Amphirhopalum cf. Tessarastrum straussii Haeckel (Fig. 7b; Plate II, 4; Plate IV, 1, 2). Present in most samples between about 10°S and 46°S; most abundant between 20°S and 46°S; see Appendix. Amphirhopalum ypsilon Haeckel (Fig. 7c; Plate II, 5). Present in samples north of about 25°S, except for four samples in the eastern part of the study area between about 30°S and 25°S. Trigonastrum sp. (Fig. 7d; Plate II, 6; Plate IV, 16, 17). Consistently present in samples between about 27°S and 46°S with a northward extension of its geographic range to about 18°S in the western part of the study area; see Appendix.

PLATE I (× 140) 1. Acrosphaera flammabunda (Haeckel), LSDA 120G(b), D26/0. 2. Acrosphaera lappacea (Haeckel), A I I 15766HC, E37/2. 3. Acrosphaera spinosa (Haeckel), A I I 93-11PC, L48/4. 4. Buccinosphaera invaginata Haeckel, A I I 93-11PC, W32/2. 5. Collosphaera huxleyi Muller, A I I 15-766HC, G31/4. 6. Collosphaera sp. aff. C. huxleyi Muller, RC9-161 TW, R16/1. 7. Collosphaera macropora Popofsky, A I I 93-11PC, F37/2. 8. Collosphaera tuberosa Haeckel, A I I 93-11PC, G29/0. 9. Disolenia quadrata (Ehrenberg), A I I 93-11PC, $39/0. 10. Disolenia zanguebarica (Ehrenberg), A I I 93-11PC, K42/2. 11. Otosphaera auriculata Haeckel, RC 9-161 TW, M31/1. 12. Siphonosphaera polysiphonia Haeckel, A I I 93-4PC, X19/0. 13. Actinomma antarcticum (Haeckel), RCll102TW, M35/4. 14. Actinomma arcadophorum Haeckel, V14-103P, P25/4. 15. Actinomma medianum Nigrini, RC11-100P, N14/1. 16. Anomalacantha dentata (Mast), LSDA 125G, G18/2. 17. Ommatartus tetrathalamus tetrathalamus (Haeckel), RC9-161TW, W45/1. 18. Cypassis irregularis Nigrini, A II 15-596FF, M20/3. 19. Saturnalis circularis Haeckel, RCll-102TW, U40/0. 20. Spongurus cf. elliptica (Ehrenberg), A I I 93-4PC, L48/4. 21. Spongurus pylomaticus Riedel, RC ll-100P, G43/0. 22. Spongocore puella Haeckel, A I I 93-4PC, C29/0.

122

-~

b

j,

in(31a

. . . . . -. . . . .

~ I f .........

ndla

I

I"

J 0 0 . , ~

Arab,a

"

0

'

,Africa

g°°~

~0%

J

~

|

Arabia

..,- ~

_,

.

,

;ndl;}

;

"

C)

~,<,di ~':.........7..o**

Africa

¢

/

O0

~

Arab*a

"

Africa

v"

O•

-,,'~ ?

•

•

O

O o

e

•

•

'\

'*~i'

•

•

~

:iii

•

~

~

•

g/ • ~'~'

•

•

• •

"

0

©-

o

C -

O

0 o %

A

0 0

,;]

1

o

COLLOSR-IAERA ~CROPORA

Q 0 ©

(a L

.

.

.

.

.

D I SOLENI A QIJADRATA

.o

(b)

<

.

F

(c)

50%

.

- X.7

-~,

.

t

' '

COLLOSPHAERA TUBEROSA

.

.

.

.

.

Arabia

..,

. .

:

,,! '='0

AraDl~l

•

~ P°

,~

• O•

art ~.,,

q(]~a

O0 Arabia

I

""'!

oO

Indl8

[ ~

l: ~1t • Af T~ca

(....7~ ndla

•

•

.

q,]

" .......

•

• ~j

Afr+ca

O0

Q o O • O O

~, ~'~ [

•

:

• "

*

I

•

/

•

•

•

•

O*

•

~"

•

• •

•

i

•

0

o

(d)

D I SOLEN I A o o

~:~

OTOSPHAERA AUR I CULATA

ZAI~t, IJEBAR I CA

(e)

S I PHONOSPHAERA

• •

(f)

Fig. 4. D i s t r i b u t i o n p a t t e r n s o f r a d i o l a r i a n taxa. (See Fi~. 3 c a p t i o n for e x n l a n a t i n n n f ~vmh,,i~ i

POLYS I PHONI A

123 India

India T,o,~

I O Arabm

,•

Arabia

, 0

no@

: U' 0 Arabia

0

•

-

•

0

0

%

0 ir

0 C,

Africa

O

Africa

Africa

() Q

i" 0

0

0

:'1

0

.-z ,. r.~

0

;

0

/;

O *

,~e°~,' / .~,<

0 0

O O

t.

•

,

•

.

O

•

•

O 0

©

O

0

0

0

0

40°9

0

ACTI NOtilA ANTAETI CUM

o 0

(b)

70°

60°

ACT I NOMMA MEOIANUM

ACT I NONIMA ARCADOPHORUM

o

o 50°E

0

)-

O

O

(a)

J

O

O* Sno

O O

•

20°

O 0

O * *

L o

, ~/ o o ( . / / o . o, +, . oo *

r

(c)

0

<'

"k. "~

~ India

:i

/ Arabia

Ind@

India

21;01

OO

-ii_

,,, It)%J I/

•

•

•w

//

;~.~ , ~)

Arab@

f-,

,/

k 0o ,\y" Africa / /

• j

.//

20°N

0

0

• 0

k./,'

O*

°

°o *

0

o~,; '

•

•

0

,I ~ / "~,

0 0

,

O

0

"0 0

o o 0

_

O

*

O*

•

C'

0

* *

0

•

0 0

?o

0 0

• * *

30'

. ;~'

' ~'~,;

20°

0 0

0

..... ( , ~

0

© 0

(. O

..../

0 0

(e/

' !

0

10°

O

.....

O0

' ' // It

~ ~c~/

C

}, % o

Africa

o

~'

',

0 0

0

(; Q

0

O

4,/

40'S

•

O

4:

O

•

Cd)

~o[

0

e

ANOMALACANTHA •

DENTATA c)

6Co

7,Do

e e

ONtAATARTUS TETRATHALAMLIS TETRATHALAMUS

o

CY PASS I S o o

,=cfl

o

[

Fig. 5. Distribution patterns of radiolarian taxa. (See Fig. 3 caption for explanation of symbols.)

I REGULAR I S

o

124

nana O~ Arabia

Av~t

•

•

•

~O

Arabia

%

Afr v;a

Africa

,4" < ~ /

2 /

't

/

o

(

.m

o

,

,

•

•

u~ ]

o

*

(.

•

0

O*

•

•

O-

0

•

SATUI~AL I S CIRCULARIS

e

(a )

:

50°1

.o

b(:~

:.-

I\. !, "~i r 'i

Arabia ~v

/

(c)

inIla

nala Arabia

Arabia

I•

•

•

0

•

':'t

O•

i Africa / f

SPON~RUS PYLOMATICUS

(b)

J: O0

/--/

SPONBURUS OF. ELLI PTICA

¢

Ah~,.

•

Africa

i // F

•

•

•

• o

•

•

• C°

o

•

*

~0 •

~

#,,]

.

~2

•

O*

"

0~

0

0 Q

•

• •

(d)

•

S ~ O E PUELLA

STYPTOSPHAERA SPUMAOEA •

(e

Fig. 6. D i s t r i b u t i o n p a t t e r n s o f r a d i o l a r i a n t a x a {See Fig. 3 c a p t i o n for e x p l a n a t i o n o f s v m b n h

I-.IE.LIOO,SOUS

o •

ASTEPlSCUS

125 ----

-C7~ ,:: . . . .

]

] O~ , ;~'

Arabia

i

India 23%

• / •

. i D'~

"~ < :-" " f / o Arabia ~ , JO 0

'\L

~'........,;% /

Africa

~

Africa

~ j:O

I,,

\\

'.P

o

/,"

C)

3o

C

Arabia

i

!

Africa

'

/,

O

•

'

Ind,a I ,~

.~,

K . . . . "; •

©©

"~

\_

2C°N

~"

o

% F

India

•

20°N

' '2

O• •

•

°°

© •

•

©

10°

•

0

r " <;.'

•

,c~

/ ~A

0

•

•

rO°

$;',,

•

• ~

• ~o.~'

0

©

,~ O*

O 0

* * 0 Q 0

,,1

20°

~N

0 0

•

~

•

•

*

•

0

•

0

•

0

0 ~

0

~0~

•

0

20"

D

~O

e

0 *

"J

2Co

• o

o •° o

j

0 D

0

30"

O

O c

0

0

C)

0

fi, ,,,:

•

HELIODISCUS ECHINISCUS

0

Ca)

4C%

Arabia

5CI°E

~

J ~',

Arabia

_~f~'O

0

,

o

50oF

YPSILON

o ....

too

inol~

ndla • •

•

40"! AMI~ I RHOPALIJM

o

(c)

STRAUSS I I

0

0

OF. TESSARASTRUMJ

o

india t:~'h

AMPH I RHOPALUM

•

(b)

?,o

::

•

40%

Arabia

)O°N

,

0 0

0

•

,, (~)

©©

Africa

:!> i A-~a // ~'"

'V,

Africa

C O O C

O

,./~\

(//

0

if:

,

•

*

0

•

©*

O 0

ff.-

•

°

0

0

2-

o

~.

0

~cc

• •

C

0 =

•

•

0 0

0

0 40%

•

TRIGONASTRUM SP. (d)

F i g . 7. D i s t r i b u t i o n

O

(e)

°

patterns

0

O

of radiolarian

~,o~

o

O 0

EUOHITONIA ELEGANS

taxa. (See Fig. 3 caption

-

(f) for explanation

of symbols.)

EUCHITONIA FURCATA

126 aa

a

India

Q•

o o Arabia

%

¢

•l

Oo

Africa

I

•

?o ~

•

9 ,

•

•

•

. ~J~

•

•

•

~/

• •

•

•

•

•

•

I

•

•

•

•

~

•

•

•

.

•

A

DI CTYOCORYNE PROFUNDA

(a)

D I CTYOCORYNE TRUNCATUM

(b)

•

HYIEN I ASTR!J EUCLIDIS

•

(c)

Oo Arabia

•

• Q

•O AIFIC~

o o

I W

/ a i

-

M •

.

I

O I

A

I

SPONGASTER TETRAS TETRAS

(el

(d)

F i g . 8. D i s t r i b u t i o n

"

patterns

of radiolarian

SPONGOBRACHIUM SP.

SPONGASTER TETRAS

RREGULARIS

taxa. (See Fig. 3 caption

( f]

for explanation

of symbols.)

127

Euchitonia elegans (Ehrenberg) (Fig. 7e; Plate II, 7). Present in most samples north of about 20°S; very rare occurrences as far south as 37°S; frequently specimens are incomplete and cannot be distinguished from E. furcata. Euchitonia furcata Ehrenberg (Fig. 7f; Plate II, 8). Consistently present in samples north of about 25°S with occurrences as far south as about 30°S in the central part of the study area; frequently specimens are incomplete and cannot be distinguished from E. elegans. Dictyocoryne profunda Ehrenberg (Fig. 8a; Plate II, 9). Present in most samples north of about 25°S; very rare occurrences as far south as about 33°S.

Liriospyris reticulata (Ehrenberg) (Fig. 9c; Plate III, 2). Present in most samples between about 15°N and 33°S. Lophospyris pentagona pentagona {Ehrenberg) emend. Goll (Fig. 9d; Plate III, 3). Present in most samples between about 18°N and 25°S. Phormospyris stabilis (Goll) antarctica (Haecker) (Fig. 9e; Plate III, 4). Present in most samples between about 37°S and 46°S. Carpocanistrum spp. (Fig. 9f; Plate III, 5). Present in all samples between about 19°N and 45°S.

Dictyocoryne truncatum (Ehrenberg) (Fig. 8b; Plate II, 10). Present in every sample, except one, north of about 32°S.

Carpocanarium papillosum (Ehrenberg) group (Fig. 10a; Plate III, 6). Bimodal distribution; present in most samples north of about 15°S and very rare in three samples between about 37°S and 41°S.

Hymeniastrum euclidis Haeckel (Fig. 8c; Plate II, 11). Present in all samples except southernmost (about 48°S) and one impoverished sample at about 30°S.

Cornutella profunda Ehrenberg (Fig. 10b; Plate III, 7). Present in most samples north of about 46°S; however, between about 20°S and 35°S it is frequently absent or very rare.

Spongaster tetras tetras Ehrenberg (Fig. 8d; Plate II, 13). Consistently present in samples north of about 30°S.

Lithopera bacca Ehrenberg (Fig. 10c; Plate III, 8). Present in most samples between about 10°N and 35°S; particularly abundant in samples between about 22°S and 35°S; very rare in two samples between 40°S and 44°S.

Spongaster tetras Ehrenberg irregularis Nigrini (Fig. 8e; Plate II, 14). Present in most samples between about 30°S and 40°S with rare occurrences extending its geographic range to between 25°S and 45°S. Spongobrachium sp. (Fig. 8f; Plate II, 13; Plate V, 3). Present in most samples between about 10°S and 30°S; see Appendix. Larcospira quadrangula Haeckel (Fig. 9a; Plate II, 15). Present in most samples except southernmost (about 48°S) and three northernmost (about 19°N); very rare north of about 10°N. Antarctissa spp. (Fig. 9b; Plate III, 1). Present in all samples south of about 37°S.

Dictyophimus crisiae Ehrenberg (Fig. 10d; Plate III, 9). Present in most samples north of about 46°S; however, between about 15°S and 25°S it is frequently absent or very rare. Pterocanium praetextum praetexturn (Ehrenberg) (Fig. 10e; Plate III, 10). Present in all samples north of about 20°S and in most samples between about 20°S and 33°S. Pterocanium praetextum (Ehrenberg) eucolpum Haeckel (Fig. 10f; Plate III, 11). Present in all samples between about 27°S and 46°S except for one impoverished sample at about 30°S.

128 P L A T E II

129 Pterocanium trilobum (Haeckel) (Fig. l l a ; Plate III, 13). Present in most samples north of a b o u t 46°S; less abundant south of a b o u t 35°S.

A n t h o c y r t i d i u m ophirense (Ehrenberg) (Fig. 12a; Plate III, 18). Present in most samples north of a b o u t 40°S; less abundant in middle latitudes.

Pterocanium sp. (Fig. 11b; Plate III, 13). Bimodal distribution; present in all samples north of the equator; present, b u t very rare, in samples between a b o u t 30°S and 46°S.

Anthocyrtidium zanguebaricum (Ehrenberg) (Fig. 12b; Plate III, 19). Present in most samples north of a b o u t 45°S; rare or absent in several samples between a b o u t 20°S and 25°S in the eastern part of the study area.

Theocalyptra bicornis (Popofsky) sensu stricto (Fig. 11c; Plate III, 14). Present in all samples south of a b o u t 37°S; there is a similar, b u t diminutive, form in lower latitudes. Eucyrtidium acuminatum (Ehrenberg) (Fig. l l d ; Plate III, 15). Present in all samples between a b o u t 18°S and 46°S, except for two impoverished samples near 28°S; very rare occurrences extend its geographic range as far north as a b o u t 10°S; around 20°S many specimens are transitional to E. hexagonatum. Eucyrtidium hexagonatum Haeckel (Fig. 11e; Plate III, 16). Present in all samples north of a b o u t 25°S, but generally rare between a b o u t 20°S and 25°S; very rare specimens in samples as far south as 37°S. Lithocampe sp. (Fig. 11f; Plate III, 17). Present in most samples south of a b o u t 10°S, b u t consistently present and most abundant south of a b o u t 30°S; some very rare occurrences between a b o u t 0 ° and 10°S.

Androcyclas gamphonycha (Jorgensen) (Fig. 12c; Plate III, 20). Present in most samples between about 30°S and 46°S. Lamprocyclas maritalis maritalis Haeckel (Fig. 12d; Plate III, 21). Present in most samples north of about 46°S, but more abundant in middle latitudes. Lamprocyclas maritalis Haeckel polypora Nigrini (Fig. 12e; Plate III, 22). Present in most samples north of a b o u t 40°S, but frequently rare or absent between about 20°S and 30°S; most abundant in low latitudes. Lamprocyclas maritalis Haeckel ventricosa Nigrini (Fig. 12f; Plate III, 23). Present in all samples north of a b o u t 10°N. Lamprocyrtis nigriniae (Caulet) (Fig. 13a; Plate III, 24). Present in all samples north of about 5°S.

PLATE II (× 140) 1. Styptosphaera ? spumacea Haeckel, RC 11-102TW, P29/4. 2. Heliodiscus asteriscus Haeckel, A I I 93-4PC, R41/0. 3. Heliodiscus echiniscus Haeckel, CHN 100-26PG, L15/2. 4. Amphirhopalum cf. Tessarastrum straussii Haeckel, LSDA 125G, D46/3. 5. Amphirhopalum ypsilon Haeckel, A I I 93-4PC, Z34/2. 6. Trigonastrum sp., RC ll-100P, W46/3. 7. Euchitonia elegans (Ehrenberg), LSDA 120 G(b), U44/1. 8. Euchitonia furcata Ehrenberg, V14-103P, R32/2. 9. Dictyocoryne profunda Ehrenberg, RC9-161TW, W34/0. 10. Dictyocoryne truncatum (Ehrenberg), A I I 93-11PC, U42/0. l l . Hymeniastrum euclidis Haeckel, RC9-161TW, D20/0. 12. Spongobrachium sp., DODO 130G, C17/0. 13. Spongaster tetras tetras Ehrenberg, RC9-161TW, U21/0. 14. Spongaster tetras Ehrenberg irregularis Nigrini, LSDA 125G, W4214. 15. Larcospira quadrangula Haeckel, RCll-102TW, D29/2.

130

nana

-

Ina~a

ArabuP

Arabna

A iI

•

•

O• Africa

I

•

•

3 •

•

LARCOSPIRA

•

QUADRANGULA

•

(a)

•

ANTARCT I SSA •

L I R I OSPYR I S

SPP.

RETI CULATA

(c)

(b)

nala

ArAbni

•

Ar,lbh~

Arabia

•

•

•

•

•

•

s~

•

Africa

•

•

~

.:~

•

•

•

•

,,,,

• •

(d)

OV

,,,

~

~

,~-

~

•

-

LOPHOSPYRIS PENTAGONA PENTAGONA

• •

(e)

•

PHORMOSPYRIS STABILIS ANTARCTICA

•

•

•

• •

•

• • ( f )

Fig. 9. Distribution patterns of radioiarJan taxa. (See Fig. 3 caption for explanation of symbols,!

CARPOCANISTRUM SPP

131 r.

.

i

.

.

.

~ India

India \j,

~)

Arabia

i

:•

India

Arabia

'< ['i' I

, it

r .~'~ O A abgj)~JOO ~

• 15'~,

../J

Africa

Africa

j

/

t/

3'

.°

f

•

0

•

'i::

3; ?

,:

0

~ /

,. ~/.

I~,

O

O O

.~

0 .

*

O

O*

O •

, ~C°

O

•

~

~,~

O 0

•

o

o

/

.

* 0 *

0

0 0

c

o o

•

', O

•

• • *

•

#,7

i.~~'/'~

Q

•

o

o

?3'

c

0

0

0

© O

0

3C~

O

C O' © •

4 i:} g S

o

(a)

•

0 50%

I

6~ ~

(b)

73°

o

50%

6,3"

4 ¸

O

CORNUTELLA PROFUNDA

•

OARPO~ANARIU~ PAPILLOSU~ ~P.

o

4 ,t

L I THOPZRA BAOCA

0 0 0

(C)

', '°

~:~

O

4,...../ x >) India
O•

t:

Arabia

I

India

India I

2OON

\\

Arabia

•0

~

,

Arabia

O

<>,

~!

q

•

•

'

O

:'5 Africa

/

,

J

f

Africa

/

/

O•

~

. i f

Africa

)o I;

/

,D

I ~oc

O

/ vi,

G

J !

)

/

©

|

iCo

~

I i 0

a "~

0

0

0 t

/

*

~

O

O*

20°

(

0 0

'g/ "" ....

•

*

0 *

•

°0 •

0

•

~0°

.

~"

•

(}

0

c~ ©

0

/

:

':D (?

/" "(dr" ' ~ i, ~

•

* *

O O

O

0

0

*

O *

0 O

0

(}

()

()

e 0 •

40o9

0

0

D I CTYOPHI MLIS CRISIAE

(d)

o

7C°

0

(e)

5C°7

o

0 0 60~

4 )"

PTE ROCAN I UM PRAETEXTUM PRAETEXTUM ,3o

• •

PTEROCAN I UM

•

(f )

o

Fig. 10. Distribution patterns of radiolarian taxa. (See Fig. 3 caption for explanation of s y m b o l s . )

PRAETEXTUM

EUC0LnUM

132 .; ,t

~nola ~O

Arab=a

I

O•

Africa

•

•

Alrtcd

•

7_ •

~

•

:, ~ 2 ,' '

-

,

9

•

•

•

• •

$

•

o*

J

A

PTEROCAN I UM TRI LOBUM

• •

(a) i r ] !

~-

. . ~

'

,

,-

~ f~,

q

Africa

~

THEOCALYPTRA

SP.

•

(c)

9 ICORNtS

$.S.

*

.... no la

nola

•

Arab,

~ ~

(.'

/

•

PTEROCANI UM e

(b)

. . . . . . . . . . . . - %:::r-.. -. . . . , j"

Arab*a

•

Arabia

A !', !

©

O<,

"

12

~,tr~ca

Atrl(:a

t; (_ f.

n O

•

()

/,,? r'"

~i

• s

(:;'

e

') ~/~/ •

~/

(-¢

• •

~

f

,~J

•

S ,t'

•

~

•

•

•

•

•

,.

•

•

O *

•

ACUMI NATUM

I (d) L

EUCYRTI D IUM HEX~TUM

EUCYRTIDIUM •

(e) .

.

.

.

.

..

•

L I TI'-,IOCAM VE

•

(f)

.

Fig. 11. Distribution patterns of radiolarian taxa. (See Fig. 3 caption for explanation of symbols. }

SP.

133 ~Jt

India "-/°'I

Z j i~ /- / i 0

20ON Arabia

>/

/

\

2C°N

i

.-? ; . Africa

India i

\

India 2(",

y0

0

,' 00 Africa

-//

rT"

"zji }0 ,q

Arabia

.......

.

•O

/

~ J

:'

QO

/"

•

00

•

/

C=

/

0

/

@ ©

O•

0

10=

10°

•

r% j j :, •

• •

•

•

~

20°

•

o0 *

@

O0

•

•

•

o ° *

• •

~, *

"( Z/

•

•

0

0

~

©*

20°

* *

•

Q 0

C C) ©

o

o

/, ~m/

0

t

* O*

ZO

O

0

0

0

O 0

30°

;

• * 0

0 D

30°

0

•

0

ANTHOCYRTI D I IJM OPHIRENSE

0

(a)

0 0

o ~)°E

•

(b)

70° 1

60"

4cos

•

40%

ANTHOCYRTID IUM ZANC-L~BARI CUM

0

0 50°E

60°

•

(c)

70°

o

"-~ J

~ x . A "

ANDROCYCLAS

•

GAMPHONYCHA

Eo

, :,

X

,

India

India 20°N

• •

t

Indla

2o"s

h

'~,

Arab•

Arabia

. . . . :~ s •

l

T

•

•

Iti

t\ •

i0°

/ ,7'

OlD

/i/

oQ

•

o

0o

0 0 0

O •

0

I0°

• ¢'0 * • O*

•

•

2o°

•

•

?

•

10°

-

0 0

0 0 ~'~'i

0

~°°

0

0 •

*

•

*

0

~

0

*

3o"

•

0

0

a O~

O

Q

0

* *

0

* O*

0

O*

0 O

•

•

0

o o

0

?3°

0 0

O

30 o

©

0

0

0 •

0

LAMPROCYOLAS

•

(d)

40%

•

MARITALIS

•

MARITALIS

0 J

Fig. 12. Distribution

(e)

J

patterns

•

of radiolarian

50%

o

4°'s 1 LAMPROCYCLAS

/

o

MARITALIS

J

o

POLYPORA

t!

o

60 °

r'O°

taxa. (See Fig. 3 caption

0 ©

LAMPROCYCLAS

0 0 (f)

0 ~)°f

for explanation

6( °

of symbols.)

MAR, TALI S VENTR I COSA

134 P L A T E III

8

10

11 15

W

19

20

Z4

135

Lamprocyrtis (?) hannai (Campbell and Clark) (Fig. 13b; Plate III, 25). Consistently present in samples north of about 10°S with scattered occurrences as far south as 30°S. Pterocorys hertwigii (Haeckel) (Fig. 13c; Plate IV, 1). Consistently present north of about 18°S and in one sample at about 21°S. Pterocorys sabae (Ehrenberg) (Fig. 13d; Plate IV, 2; Plate V, 4, 5). Present in most samples between about 12°N and 40°S; abdomen rarely present in high-latitude specimens; see Appendix. Theocorythium trachelium trachelium (Ehrenberg) (Fig. 13e; Plate IV, 3). Present in all samples between about l l ° N and 25°S; from about 25°S to 33°S specimens are rare and transitional to T. trachelium dianae. Theocorythium trachelium (Ehrenberg) dianae (Haeckel) (Fig. 13f; Plate IV, 4). Present in all samples between about 25°S and 46°S except for one impoverished sample near 30°S; between about 24°S and 30°S specimens are transitional to T. trachelium trachelium. Botryostrobus aquilonaris (Bailey) (Fig. 14a; Plate IV, 5). Bimodal distribution; consistent-

ly present between about 35°S and 46°S; scattered occurrences between about 0 ° and 20°S.

Botryostrobus auritus/australis (Ehrenberg) group (Fig. 14b; Plate IV, 6). Present in all samples except for two impoverished samples near 28°S. Phormostichoartus corbula (Harting) (Fig. 14c; Plate IV, 7). Present in most samples north of about 33°S except for a group of five samples between about 20°S and 25°S in the eastern part of the study area; very rare occurrences as far south as about 45°S. Siphocampe lineata (Ehrenberg) group (Fig. 14d; Plate IV, 8). Present in most samples north of about 15°S; scattered occurrences between about 15°S and 26°S and very rare occurrences between about 37°S and 46°S. Spirocyrtis scalaris Haeckel (Fig. 14e; Plate IV, 9). Present in most samples north of about 18°S; absent from two northernmost samples (about 19°N). Botryocyrtis scutum (Harting) (Fig. 14f; Plate IV, 10). Present in most samples north of about 33°S.

PLATE III (× 140)

1. Antarctissa spp., RC11-102TW, X22/1. 2. Liriospyris reticulata (Ehrenberg), A I I 15-766HC, 019/0. 3. Lophospyris pentagona pentagona (Ehrenberg) emend. Goll, RC9-161TW, J29/2. 4. Phormospyris stabilis (Goll) antarctica (Haecker), RC11-102TW, D27/3. 5. Carpocanistrum spp., A II 93-11PC, 040/2. 6. Carpocanarium papillosum (Ehrenberg) group, RC9-161TW, H32/0. 7. Cornutella profunda Ehrenberg, RC9-161TW, C25/0. 8. Lithopera bacca Ehrenberg, A I I 93-11PC, C44/2. 9. Dictyophimus crisiae Ehrenberg, RC11-100P, H43/0. 10. Pterocanium praetextum praetextum (Ehrenberg), A I I 93-11PC, U46/2. 11. Pterocanium praetextum (Ehrenberg) eucolpum Haeckel, RC11-102TW, X19/2. 12. Pterocanium trilobum (Haeckel), A I I 15-766HC, C13/2. 13. Pterocanium sp., CHN 100-40PG, G17/1. 14. Theocalyptra bicornis (Popofsky) sensu stricto, RC11100P, D31/0. 15. Eucyrtidium acuminatum (Ehrenberg), A II 15-766HC, P44/3. 16. Eucyrtidium hexagonatum Haeckel, A II 93-4PC, X31/2. 17. Lithocampe sp., A I I 15-766HC, F27/3. 18. Anthocyrtidium ophirense (Ehrenberg), RC9-161TW, N43/2. 19. Anthocyrtidium zanguebaricum (Ehrenberg), A I I 93-11PC, R38/4. 20. Androcyclas gamphonycha (Jorgensen), RCll-102TW, 020/0. 21. Lamprocyclas maritalis maritalis Haeckel, A II 15-766HC, Q45/2. 22. Larnprocyclas maritalis Haeckel polypora Nigrini, A II 93-4PC, T16/0. 23. Larnprocyclas maritalis Haeckel ventricosa Nigrini, RC9-161TW, G28/4. 24. Lamprocyrtis nigriniae (Caulet), RC9161TW, G47/4. 25. Lamprocyrtis (?) hannai (Campbell and Clark), RC9-161TW, R47/0.

136

I]Ola

no la O•

. • ~QO

Arabia

• ,

•o

Ara D{a

•

%

{ • v

O•

A~tiCO

Africa

O

0

('

•

Afr Ca,

A

•

•

•

0 O

0 0

0 0

0

( i•

O C

y

C)

0

O* O O

0

0

O L ~ Y R T

o

(a)

4,,o

o o

o

(b)

60. L

(,~

- - -

~,~ --~0

"~ A r . ' a ~ t \ L ~-'f o 4~..-; % • Africa

/

~

LAMPROGYRTf S HANNA

IS

NIP_iRINIAE

~-

PTEROCORYS HERTWIGI I

(c) ~. ~ . ~

-. . . . . . . . . . . .

T..~

" "

India

India

mcj,d

~>O°N J

0

Arabia

Arabsa

•

•0

Africa

j~//

Africa

•

Q •

o •

*

~0

3

~o"

•

•

~

•

©*

•

o

•

e/

20"

•

0

•

00

(; t .j

•

*

°

O x

•

•

i_

•

O-

•

~oo

•

$

4()°S

o

PTEROCORYS

o o o (d)

50oE

o

•

. L

B

$ABAE

(e )

60°

Fig. 13. Distribution

patterns

of radiolarian

THEOCORYTHI UM TRACNEL I UM TRhCHEL;UM

taxa. (See Fig. 3 caption

o

(f)

for exolanation

of .~vmhnl¢

THEOCORYTHI UM TRACt,EL I U~ DIANAE

137

[ ~

'

' %,[

India

O•

)_:<} Africa /

o .

/

Arabia

%

i I,

•

20°N

20°N

Arabia

oO

O

Afr,~///'

O•

o

/•

•

•

•

10°

•

~o °

d •

0 ~

° ~

0"

*

0

0 •

•

•

•

~c,°

.c'\

•

~ i

•

o

20°

o 0 o 0

© *

'

o

0

•

"

•

•

•

•

~

20"

/ ~ / ~ /

•

~"

0.

•

0.

•

°

0

•

•

0•

0

0

~°°

O 0

0

0

30°

©

•

*

s0o

•

30~

© ©

•

•

o

60°

I

(b)

70°

i

[

•

50°E

.

.

.

60"

.

40°S

,

,

i

\

o

4cos

PHORMOSTI CHOARTUS %

(c)

o

~O°E

CORBULA

60°

70°

, i

'~I

0

0

BOTRYOSTROBUS AUR I T U S / AUSTRALI S GP. 70°

BOTRYOSTROBUS AQUI LONARI S

•

(a)

•

40%

India

~

\.

"~

India

20°N Arabia j , ~

] ~0

)°N

Jr°;

Arabia..f

/-

o

20°N x

> Q ~~'O©

i

o

•

0 •

0 0

•

0

~

20°

0.

0 0

0

o e 0

©

0

O*

*

©

0 *

0 ©

0 0

0 *

10o

© 0

0

20o

20°

0 0

0 0

0

(3.

0

30°

0

•

•

10°

0

~0

••

/

0 0

'\

,j

Africa / f / /J

10°

•

O

'<

0• -

•

Arabia

30°

©

30°

0

0 O 0

40%

O

S I PI-IOCAMI:E

o

O

LI NEATA GP.

(d)

50°E i

0

60°

Fig. 14. Distribution

70~ patterns

O 0

(e) of radiolarian

I0°[

o

O O 600

40% SP I R00YRT I S SCALAR I S tOo

taxa. (See Fig. 3 caption

O

O O

'

(f)

for explanation

o of symbols.)

O O

40% BOTRYOOYRT I S SOUTUM 70°

i

J38

PLATE IV

t •

k.

Ai,,

I 8

10

11

12

139 thermophila Petrushevskaya (Fig. 15a; Plate IV, 11). Consistently present in samples between a b o u t 10°N and 18°S; very rare occurrences e x t e n d its geographic range to ab o u t 30°S. Centrobotrys

Saccospyris c o n i t h o r a x Petrushevskaya (Fig.

15b; Plate IV, 12). south o f a b o u t 37°S.

Present in all samples

Recurrent group analysis Following the procedures of recurrent group analysis which were used previously by Nigrini (1970) for North Pacific Radiolaria, r e c u rr en t groups were identified among the 74 taxa used in our study. The t h e o r y of rec u r r e nt group analysis and the assumptions involved have been discussed elsewhere (Fager, 1957; Fager and McGowan, 1963; Renz, 1976), and will be briefly summarized here. R e c u r r e n t group analysis uses the c o n c e p t o f affinity, based on co-occurrence of species (presence or absence only) as a means of identifying those species t ha t are considered to be a nearly constant part of each others" biological environment. Those species which often co-occur have a strong affinity; those t h a t never do, have no affinity. R ecur r ent group analysis leads to the largest, most fre.quent, separate units within which each species shows a strong affinity for all others. F o r any two species A and B, the index of

their affinity is given by: I.A.-

J

1

x/NA X N B

x/-2 NB

where J = n u m b e r of joint occurrences of A and B; NA = total n u m b e r of occurrences of A; NB = total n u m b e r of occurrences of B; and N B ~> N A. Fager (1957) defines a recurrent group as one t h a t satisfies the following requirements: (1) The index of affinity is ~>0.50 for all pairs of species within the group; (2) the group includes the greatest possible n u m b e r of species; (3) if two or more groups with the same n u m b e r of species and with members in c o m m o n are possible, the one for which the sum of affinities is greatest is chosen. To i m pl em ent this procedure, the c o m p u t e r program RE G RO U P (designed by E.W. Fager) was used. The program c o m p u t e d the n u m b e r of occurrences and joint occurrences of the 74 species identified in our transect of 46 samples. It then calculated an index of affinity for each pair of species, and c o m p a r e d this n u m b e r to the assigned c u t o f f value (0.50). If this index is equal to or greater than the assigned c u t o f f value, the pair of species is considered to have affinity. The program then determines the recurrent groups according to the three criteria of Fager (1957) summarized above. In our study, five recurrent groups of Radiolaria were selected (Table II). Groups A,

PLATE IV (x 140 unless otherwise noted) 1. Pterocorys hertwigii (Haeckel), ANTP 142PG, U20/3. 2. Pterocorys sabae (Ehrenberg), AII 93-11PC, K42/0. 3. Theocorythium trachelium tracheliurn (Ehrenberg), A I I 93-11PC, T33/2. 4. Theocorythium trachelium (Ehrenberg) dianae (Haeckel), RCll-102TW, L30/2. 5. Botryostrobus aquilonaris (Bailey), A II 93-4PC, J42/0. 6. Botryostrobus auritus/australis (Ehrenberg) group, A II 93-4PC, G34/0. 7. Phormostichoartus corbula (Harting), A I I 93-11PC, P47/4. 8. Siphocampe lineata (Ehrenberg) group, AII 93-11PC, F29/1. 9. Spirocyrtis scalaris Haeckel, CHN 100-26PG, X22/3. 10. Botryocyrtis scutum (Hatting), A II 93-11PC, C22/2. 11. Centrobotrys thermophila Petrushevskaya, A I I 93-11PC, N14/3. 12. Saccospyris conithorax Petrushevskaya, RCll102TW, U20/3. 13. Collosphaera huxleyi Muller, RC17-93P, R18/0; x 275. 14. Collosphaera sp. aff. C. huxleyi Muller, A I I 15-597FFA, C12-4; x 275. 15. Collosphaera rnacropora Popofsky, CHN 100-29PG, T40/1; x 275. 16, Trigonastrumsp.,RCll-lOOP, P30/3. 17. Trigonastrum sp.,RC11-102TW, Dll/0;X 275.

140

ndla

I

"-~

(, Arabia

'

_~ )

,-4

India

Arabia

}, .. ~ . -~

Africa

'/-

0

,"

0

"T"I'i

•0

()

• ,(J Atrlca

(, ,3°

(T

C)

O O

i(] o

• 0

¢'° "t

0 0 d i {; ~ is'

~

~,'

0

0 @

•

,

0

0

0

0

0

O* 0

0 0

0

20°

0

0

0 0 $0 °

0

(>

© C

40°S

,D

(a)

o 50%

Fig.

15.

SACCOSPYR I S CON I THORAX

CENTROSOTRYS

O O O

~0°

TI-ERMOPH IL A I

b

*

~oo

i

Distribution patterns of radiolarian taxa. (See Fig. 3 caption for explanation of symbols.)

B, and C met all the criteria specified for selection by the REGROUP program. Groups D and E were recognized by the authors, even though some affinity indices for the pairs in each group did not meet the 0.50 cutoff criterion. Group D was selected because of the unusually limited geographic distribution pattern of each of the four taxa in the group (Figs. 3e, 5f, 12f, and 13a). Affinity indices for the six affinity pairs present in Group D range from 0.42 to 0.74, and average 0.60. Group E was selected because of the intriguing bimodal distribution pattern of its five taxa (Figs. 5c, 5d, 6a, 10a, l l b ) . The taxain Group E have affinity indices ranging from 0.49 to 0.67, and average 0.57. Six species remain ungrouped (Table II). These taxa had affinities

with some members of groups, but not with all the members of any one group. After the designation of recurrent groups, we identified the samples in which each recurrent group appears, using the criterion that a group is considered "present" in a given sample if at least 80% of the taxa within the group are present. Accordingly, Group A is considered to be present in a sample if 36 of its 43 taxa are present; Group B requires 7 of its 8 species; Group C requires 7 of its 8 species; Group D requires 4 of its 4 species; and Group E requires 4 of its 5 species. The distribution patterns of the five recurrent groups are shown in Fig. 16. From the geographic distribution of the recurrent groups, we designated eight radio-

141

TABLE II Listing of recurrent groups in western Indian Ocean transect

Group A: Tropical latitudes (43 species)

Group B: Temperate latitudes (8 species)

Acrosphaera flammabunda Acrosphaera lappacea Acrosphaera spinosa Actinomma arcadophorum A mphirhopalum ypsilon Anthocyrtidium ophirense Anthocyrtidium zanguebaricum Botryocyrtis scutum Botryostrobus auritus/australis group Carpocanistrum spp. Centrobotrys therrnophila Collosphaera tuberosa Cornutella profunda Dictyocoryne profunda Dictyocoryne truncatum Dictyophimus crisiae Disolenia quadrata Disolenia zanguebarica Euchitonia elegans Euchitonia furcata Eucyrtidium hexagonatum Heliodiscus asteriscus Heliodiscus echiniscus Hymeniastrum euclidis Lamprocyclas maritalis polypora Lamprocyrtis (?) hannai Larcospira quadrangula Liriospyris reticulata Lophospyris pentagona pentagona Ommatartus tetrathalamus tetrathalamus Otosphaera auriculata Phormostichoartus corbula Pterocanium praetextum praetextum Pterocanium trilobum Pterocorys hertwigii Pterocorys sabae Siphocampe lineata group Siphonosphaera polysiphonia Spirocyrtis scalaris Spongaster tetras tetras Spongocore puella Spongurus cf. elliptica Theocorythium tracheliurn trachelium

Actinomma antarcticum Androcyclas gamphonycha Antarctissa spp. Phormospyris stabilis antarctica Saccospyris conithorax Spo ngu rus pylo maticus Styptosphaera (?) spumacea Theocalyptra bicornis Group C: Subtropical and temperate latitudes (8 species)

Amphirhopalum cf. Tessarastrum straussii Eueyrtidiurn acuminatum Lamprocyclas maritalis maritalis Lithocampe sp. Pterocanium praetextum eucolpum Spongaster tetras irregularis Theocorythium trachelium dianae Trigonastrum sp. Group D: Arabian margin (4 species)

Collosphaera huxleyi Cypassis irregularis Lamprocyclas maritalis ventricosa Lamprocyrtis nigriniae Group E: Bimodal distribution (5 species)

Actinomma medianum Anomalacantha dentata Carpocanarium papillosum group Pterocanium sp. Saturnalis circularis Ungrouped taxa

Botryostrobus aquilonaris Buccinosphaera invaginata Collosphaera macropora Collosphaera sp~ cf. C. huxleyi Lithopera bacca Spongobrachium sp.

142 -

(

?

.

md~a I

I,.

i~Oo Arabia

•

'~

%.-~'--] • Africa

// /2"

Ar~-ib~a

., '~

Arabia

Fi

~

"i Africa

/

./

d

g

• 20" i

o,

0 0

£~/

g" o

@/

g:

~-~"

3C

0

0

©

0 ©

• •

0 4)oq

0

0 0 0 f:,0,E

"X~

RECURRENT GROUP A 43 SPP.

0 0

•

RECURRENT GROUP B 8 SPP.

• •

60°

•

•

.

.

%

-.~ !

I~

•

.5

A

Arabtd

~/:,~

1 2 L J .... 9

~'I

.

" 9,

Africa

A|r c a

/

/

/

(_

•

f

•f ' . ~ / I

3

#~

i ooq \ .,.J

° ©

C

'" ,"J

r-

"~_._. RECURRENT GROUP D 4 SPP.

• • •

RECURRENT GROUP E 5 SPP.

.

RECURRENT GROUP C 8 SPP.

143 larian assemblages for the western Indian Ocean transect (Fig. 17a). Although the number o f samples e x a m i n e d is n o t sufficient t o establish the zonal e x t e n t of each assemblage, it is likely th at the assemblage boundaries do in fact e x t e n d in directions which parallel the major oceanographic frontal zones (see Fig. 1). The designated assemblages are: Arabian assemblage -- R e c u r r e n t group D only. Assemblage is characteristic of the upwelling zone east o f the Arabian Peninsula. There is no evidence t h a t it continues eastward into the northeastern Arabian Sea, although its e x t e n t is difficult to establish because of p o o r preservation o f radiolarians in sediments f r om the Indus Cone (Nigrini, 1974). S o u t h Arabian assemblage -- R e c u r r e n t groups A, D and E. Since it is based on only one sample, this assemblage is obviously n o t well established. More extensive sampling in the transition zone between the distinctive Arabian and Tropical assemblages is required t o ascertain the geographic e x t e n t of this assemblage. Tropical assemblage -- R ecur r ent groups A and E. Assemblage is diverse with a southern limit corresponding to the sharp h y d r o c h e m ical f r o n t at 10°S.

of the subtropical gyre (see Table I), none of our recurrent groups was f o u n d to be present (using the 80% c u t o f f criterion). We presume that this assemblage extends eastward from our transect into the eastern Indian Ocean (Fig. 17a). T e m p e r a t e assemblage -- R e c u r r e n t group C only. Assemblage appears to be characteristic of the southern, eastward-flowing limb of the subtropical gyre. The transition between the subtropical and t e m p e r a t e assemblages southeast of Madagascar (Fig. 17a) is n o t sharply defined due to p o o r sample preservation. Transitional assemblage -- R e c u r r e n t groups C and E. Assemblage is partially defined by the southern p o r t i o n of bimodally distributed G roup E. It extends from a b o u t 35°S to the Subtropical Convergence. Subpolar assemblage -- Recurrent Groups B, C and E. Assemblage can be identified with the eastward flow between the Subtropical Convergence and Antarctic Convergence. It is the only assemblage in which all eight taxa of G r o u p B are found. Sediments to the south of this region (between ~48° S and 56°S) are p r e d o m i n a n t l y diatomaceous with insufficient Radiolaria for reliable identifications. Discussion

Subtropical assemblage -- R e c u r r e n t group A only. Samples containing this assemblage lie within the n o r t h e r n limb of the subtropical gyre. It is possible t ha t its areal e x t e n t includes the Madagascar and Mascarene Basins, but preservation o f skeletal material in these regions is very p o o r (Fig. 17a). Central assemblage -- No r e c u r r e n t groups present. Although Radiolaria are c o m m o n and generally well preserved in the central por t i on

The identification of eight distinctive radiolarian assemblages across a north- s o u t h transect (Fig. 17a) represents a significant extension of the previous investigations of radiolarian biogeography of Nigrini (1967) and Petrushevskaya (1967, 1971, 1973). Increased availability of samples, recent refinements in the t a x o n o m y of m o d e r n Radiolaria (Nigrini and Moore, 1979), and the use of recurrent group analysis have aided significantly

Fig. 16. Distribution patterns of the five selected recurrent groups of Radiolaria. A recurrent group is considered to be "present" (filled circles on map) if at least 80% of the taxa within the group were present in a given sample. These five recurrent groups account for 68 of the 74 taxa examined during this study.

144

RADIOLARIAN

FORAMIN I FERAL ASSEMBLAGES

ASSEivIEILAG ES

ARABI AN

< / , ,0~ia r

no~a

o°~,

•

Arat),a

~ /

~S.

," ~ } i

Arabia ,

/

i

!

ARABI AN

/

.....

%;.

TROPICAL ///

•

[

$4

• 000

-

;" \ . '

•

•

•

),

/

•

i

SUBTROPICAL

!, #"_@~ Y ~''.~

-~

~

S3

0"

~ CENTRAL

©

\ "\

TRANSITIONAL

$2

,

,

~

o~ •

SUBPOLAR •

,

$I

5()°F

60°

• ~ o~J ,

j i

i

o e

7C~

Fig. 17. a. Radiolarian assemblages in the western Indian Ocean, chosen on the basis of the presence of one or more recurrent groups: "Arabian" assemblage: Group D only. "South Arabian" assemblage: Groups A + D + E . "Tropical" assemblage: Groups A+E. "Subtropical" assemblage: Group A only. "Central" assemblage: No recurrent groups. " T e m p e r a t e " assemblage: Group C only. "Transitional" assemblage: Groups C + E. "Subpolar" assemblage: Groups, B, C and E. Poor preservation of radiolarians in the region southeast of Madagascar, and low abundances between 47°S and 56'~S (Table I), did not allow the designation of assemblages in these regions, b. Distribution pattern of planktonic foraminiferal assemblages in surface sediments, modified after B@ and Hutson (] 977, fig. 49).

in

the selection of unique assemblages. It is n o t e w o r t h y that four principal oceanographic fronts in the western Indian Ocean are all reflected by boundaries between characteristic radiolarian assemblages. Strong upwelling zones are present off the Somali and Arabian coasts (Swallow and Bruce, 1966; Warren et al., 1966; Wyrtki, 1973). The Arabian upwelling zone is clearly marked by the four taxa in recurrent group D (Fig, 16), each of which has also been reported from a relatively small region of upwelling in the

eastern equatorial Pacific (Nigrini, 1968). From the present study it appears that the Arabian assemblage does not extend southward to the Somalian upwelling zone, perhaps as a consequence of the strong differences in the salinity characteristics of the two upwelling areas. The South Equatorial Divergence near 10°S is a pronounced hydrochemical front (Wyrtki, 1973), and is marked by the Tropical/Subtropical Assemblage boundary. The Transitional Assemblage appears to correspond

145 approximately with the Subtropical Convergence between 38°S and 40°S, although this relationship is imprecise because of seasonal migrations of the S.T.C. (Prell et al., 1979) and the lack of good core top samples from this region. The Antarctic Convergence near 48°S is well marked by the boundary between the Subpolar Assemblage to the north and the radiolarian-poor diatomaceous ooze assemblage to the south. The central portion of the subtropical gyre appears to be well delineated by a radiolarian assemblage in which none of the designated recurrent groups are present. The southward-flowing limb of the subtropical gyre to the east of the Madagascar includes the transition from the Subtropical to Temperate Assemblages (Fig. 17a). However, poor sample preservation, probably resulting from the highly corrosive polar b o t t o m water within the Madagascar and Mascarene Basins {Warren, 1974, 1978), makes it impossible to locate precisely the position of this transition. B~ and Hutson (1977) analyzed foraminifera in the plankton and surface sediments of the western Indian Ocean, and selected five assemblages of foraminifera characteristic of the surface sediments. In examining their assemblage boundaries (Fig. 17b) together with those selected from radiolarian distributions (Fig. 17a), the following comparisons can be made: (1) B~ and Hutson (1977) were n o t able to discriminate the upwelling zone off Arabia. More recent work by Prell (1978) and Hutson and Prell (in press), however, suggests that foraminifera in this region may in fact have distinguishing characteristics. Using an improved data base of sea surface temperatures, an expanded number of core top samples, and two new paleoecological transfer functions, these authors were able to select two new foraminiferal assemblages characteristic of upwelling within the Benguela Current (off Southwest Africa) and along the SomaliArabian coasts. We have n o t found a unique assemblage characteristic of the Benguela Current, and our Arabian Margin assemblage does not appear to extend as far south as the Somali coast.

(2) The major oceanographic front at 10°S and 40°S are apparently reflected in the distributions of both microfossil groups. The differences in how the assemblage boundaries are drawn (Fig. 17) may reflect sample coverage and n o t real differences in the position of faunal gradients. An extension of the radiolarian assemblage boundaries into the eastern Indian Ocean will aid in determining if there are significant differences in location between foraminiferal and radiolarian assemblage boundaries. (3) The foraminiferal assemblage boundary near 30°S, southeast of Madagascar, is not well defined by Radiolaria because of poor sample preservation. The oceanographic significance of the exotic Arabian assemblage will require more extensive investigation. The four radiolarian taxa characteristic of this region were also reported in the eastern tropical Pacific (Nigrini, 1968), and therefore seem to have an affinity for zones of strong upwelling (though they are apparently not present in the Somalian upwelling zone). B~ and Hutson (1977, p. 380) reported that the northern Indian Ocean is characterized by the presence of three extant foraminiferal taxa (Globo-

quadrina hexagona, G. conglomerata, Globigerinella adamsi) which are no longer living in the Atlantic, and suggested that the northern Indian Ocean may be a refuge for certain "relict" species. We see no evidence that this is the case for radiolarians. In our examination of Pleistocene and pre-Pleistocene cores from the Indian and Pacific Oceans, we have seen no evidence that the four taxa in our Arabian assemblage became extinct at an earlier time elsewhere. Clearly the Arabian Sea represents an exotic environment for faunal biogeography, and a more extensive study on the characteristics and oceanographic significance of the fauna in the region would be interesting. The bimodal distribution pattern of recurrent group E (Fig. 16) is particularly intriguing. Although the same taxa are characteristic of both the northern and the southern regions of

146 occurrence o f the group, t hey are noticeably more c o m m o n in the southern portion. The b o u n d a r y f o r the group near 10°S corresponds closely with the h y d r o c h e m i c a l f r o n t (Wyrtki, 1973), and the o t h e r boundaries for the group in the Arabian Sea, near 35°S, and near 48°S closely ap p r o x imat e ot her first-order oceanographic transitions. However, the reasons for a bimodal distribution pattern are n o t at all obvious. F r o m our sample control, we are reasom ably c o n f i d e n t th at the two areas of occurrence of Gr o u p E are in fact geographically separate, at least in the western Indian Ocean (Fig. 16). We suspect that the same is true for the eastern Indian Ocean, since meridional c u r r en t flow tends to be more intensified on the western and weakened on the eastern sides o f the ocean basins; hence a " c o n n e c t i o n " between the two areas of Recurrent Group E should be mo r e obvious on the west, but we see no such connection. It is possible that a c o n n e c t i o n exists between Madagascar and the African continent, but our present sample coverage does n o t permit us to examine this possibility. One possible, perhaps fanciful, interpretation of the bimodal pattern of G r oup E is that it represents the r e c e nt separation of a formerly contiguous distribution. The greater abundance of the species of G r oup E in the southern p o r tio n o f the pattern suggests that the taxa in the group m a y be most representative of more southerly (i.e., 35°S to 48°S) latitudes today, but at some earlier time the group m a y have e x t e n d e d more or less continuously into equatorial waters. At some time, the developm e n t of the southern Subtropical Gyre may have geographically divided the assemblage. The late Cenozoic d e v e l o p m e n t o f the monsoonal circulation could have re-enforced the separation by driving the equatorial water n o r t h w a r d (during the more intense s um m e r monsoon), and t h e r e b y inhibiting nor t h .... south exchange across the f r o n t at 10°S. A final p o i n t worth noting is the sharp drop in tad}olaf}an abundance near 48°S, corresponding with the Antarctic Convergence. Numerous investigators (e.g. Hays, 1965;

Petrushevskaya, 1973; Lozano and Hays, 1976; Morley, 1977; Dow, 1978) have studied radiolarian assemblages in the circumpolar current south of the Antarctic Convergence, but to our knowledge there have been no reports of dramatic decreases in radiolarian abundance at the Antarctic Convergence. A~ extension o f our investigation into the eastern Indian Ocean will allow us to d o c u m e n t more extensively the e x t e n t of this phenomena. We do not know w h e t h e r this represents a real difference in the p h y t o p l a n k t o n / z o o p l a n k t o n ratio, or w het her it represents selective dissolution within the water column prior to final deposition of the skeletal remains. Appendix: t a x o n o m y The following species are described and illustrated in Nigrini and Moore (1979): Acrosphaera flammabunda (Haeckel) ( =Polysolenia flammabunda ) Acrosphaera lappacea (Haeckel) ( =Polysolenia lappacea ) Acrosphaera spinosa (Haeckel) (= Polysolenia spinosa ) Actinomma antarcticum (Haecket) Actinomma arcadophorum Haeckel Actinomma medianum Nigrini Androcyclas gamphonycha (Jorgensen) Anomalacantha dentata (Mast) Antarctissa spp. [includes A. denticulata (Ehrent)erg) and A. strelkovi Petrushevskaya] Amphirohapalum ypsilon Haeckel (see also ~:'emarks

herein) Anthocyrtidium ophirense (Ehrenberg) Anthocyrtidium zanguebaricum (Ehrenberg) Botryocyrtis scutum (Harting) Botryostrobus aquilonaris (Bailey} Botryostrobus auritus[australis (EhrenberR} group Carpocanarium papillosum (Ehrenberg) grou.L~ Carpocanistrum spp. Collosphaera tuberosa Haeckel Dictyocoryne profunda Ehrenberg Dictyocoryne truncatum (Ehrenberg) Dictyophirnus crisiae Ehrenberg Disolenia quadrata (Ehrenberg) Disolenia zanguebarica (Ehrenberg) Euchitonia elegans (Ehrenberg) Euchitonia furcata Ehrenberg Eucyrtidiurn acurninatum (Ehrenberg) Eucyrtidium hexagonatum Haeckel Heliodiscus asteriscus Haeckel

147

Hymeniastrum euclidis Haeckel Lamprocyclas maritalis maritalis Haeckel Lamprocyclas maritalis Haeckel polypora Nigrini Lamprocyclas maritalis Haeckel ventricosa Nigrini Lamprocyrtis (?) hannai (Campbell and Clark) Lamprocyrtis nigriniae (Caulet) Larcospira quadrangula Haeckel Liriospyris reticulata (Ehrenberg) Lithocampe sp. Lophospyris pen tagona pentagona (Ehrenberg) emend.

FAMILY COLLOSPHAERIDAE Muller 1858 Genus Acrosphaera ttaeckel 1881 The generic name Polysolenia Ehrenberg has been used incorrectly in a number of publicatons (Campbell, 1954; Nigrini, 1967, 1968, 1970; Nigrini and Moore, 1979, etc.). The correct generic name for collosphaerids with irregularly scattered spines is Acrosphaera (cf. Strelkov and Reshetnyak, 1971).

Goll

Ommatartus tetrathalamus tetrathalamus (Haeckel) Otosphaera auriculata Haeckel Phormospyris stabilis (Goll) antarctica (Haeckel) Phormostichoartus corbula (Harting) Pterocanium praetextum (Ehrenberg) eucolpum Haeckel

Pterocanium praetextum praetextum (Ehrenberg) Pterocanium trilobum (Haeckel) Pterocanium sp. Pterocorys hertwigii (Haeckel) Siphonosphaera polysiphonia Haeckel Spongaster tetras Ehrenberg irregularis Nigrini Spongaster tetras tetras Ehrenberg Spongocore puella Haeckel Spongurus cf. elliptica (Ehrenberg) Spongurus pylomaticus Riedel Styptosphaera ? spumacea Haeckel Theocalyptra bicornis (Popofsky) Theocorythium trachelium (Ehrenberg) dianae (Haeckel)

Theocorythium

trachelium trachelium (Ehrenberg)

The following species are described and illustrated in Nigrini (1967):

Centrobotrys thermophila Petrushevskaya Cornutella profunda Ehrenberg Heliodiscus echiniscus Haeckel Lithopera bacca Ehrenberg Saturnalis circularis Haeckel Spirocyrtis scalaris Haeckel (see also Nigrini, 1977) The following species are described and illustrated in the publications cited:

Buccinosphaera invaginata Haeckel in Nigrini, 1971 (see also Knoll and Johnson, 1975)

Cypassis irregularis Nigrini in Nigrini, 1968 Saccospyris conithorax Petrushevskaya in Petrushevskaya, 1965

Genus Collosphaera Muller 1855

Collosphaera huxleyi Muller (Plate I, 5; Plate IV, 13). Collosphaera huxleyi Muller, 1855, p. 238; 1858, p. 55, pl. 8, figs. 6--9; Strelkov and Reshetnyak, 1971, p. 332, text-figs. 19--21, pl. 4, figs. 21, 23. Numerous variants of this species have been described by several authors (cf. Strelkov and Reshetnyak, 1971). The form here recognized is restricted to a simple sphere 120--160 um in diameter with small, irregularly shaped pores, 98--113 on a half equator. The shell may be slightly misshapen, but noL as pronouncedly as C. tuberosa. Thus defined C. huxleyi has a very restricted latitudinal range (about 18-3T~S (see Fig. 3e) in the Indian Ocean.

Collosphaera

sp. aff. C. huxleyi Muller (Plate I, 6;

Plate IV, 14).

Description: Shell smooth, a simple sphere 120--160 pm in diameter, with 5--8 pores on a half equator; pores vary in size, but most are larger than those of typical C. huxleyi. Shell is more perfectly spherical than C. huxleyi. Remarks: This species is c o m m o n in samples close to the Arabian coast (Fig. 3f). Rarely, in samples from about 0 to 10°S, a form transitional between C. sp. aff. C. huxleyi and C. macropora has been observed.

Collosphaera macropora Popofsky (Plate I, 7; Plate IV, 15).

Collosphaera macropora Popofsky, 1917, p. 247, text-figs. 5,6, pl. 14, figs. 2a--c; Strelkov and Reshetnyak, 1971, p. 337, pl. 4, figs. 30, 31. Description: Shell smooth, usually spherical, 92--120 ttm in diameter, with large pores, 3--4 on a half equator. Small pores may be present between the larger ones. Remarks: In the study area this species has been found to have a very restricted latitudinal range (about5 Sto2OS).

Siphocampe lineata (Ehrenberg) group in Nigrini, 1977 The following species, used in the present study, have not previously been described or require some remarks in addition to already published descriptions.

FAMILY SPONGODISCIDAE Haeckel 1862, emend. Riedel 1967 The next three species are probably closely related. However, Haeckelian taxonomy requires that one of

148

t h e m , a t least, be p l a c e d in a d i f f e r e n t genus. Until a c o m p r e h e n s i v e s t u d y c a n be m a d e , we will r e t a i n t h e classification o f Haeckel. G e n u s Amphirhopalum Haeckel 1881, e m e n d . Nigrini 1974.

Amphirhopalum ypsilon Haeckel (Plate II, 5). Amphirhopalum ypsilon Haeckel, 1887, p. 5 2 2 ; Nigrini, 1967, p. 35, pl. 3, figs. 3 a - - d ; Nigrini, 1971, p. 447, pl. 34.1, figs. 7a--c; Nigrini, 1974, p. 1065, pl. 6, fig. 3. Previously p u b l i s h e d d e s c r i p t i o n s of this species are a d e q u a t e . T h e r e is a P l i o c e n e species, Amphirhopatum virchowii (Haeckel), d e s c r i b e d by D u m i t r i c a ( 1 9 7 3 , p. 835, pl. 9, figs. 2 , 4 , pl. 11, fig. 6, pl. 21, figs. 3 13), w h i c h m a y be t h e a n c e s t o r o f A. ypsilon (cf. Nigrini, 1 9 7 4 , pl. 1065).

Amphirhopalum cf. Tessarastrum straussii Haeckel (Plate II, 4; Plate V, 1,2).

Tessarastrum straussii Haeekel, 1887, p. 547, pt. 45, fig. 8.

Description: Shell bilaterally s y m m e t r i c a l with two o p p o s i t e c h a m b e r e d arms, o n e or b o t h o f w h i c h m a y be f o r k e d distally (usually o n l y one). A r m s arise from a central structure composed of two concentric spheres a n d o n e o u t e r o b l a t e s p h e r o i d , all q u i t e s m o o t h a n d c o n n e c t e d by n u m e r o u s d i s c o n t i n u o u s radial b e a m s a n d p e r f o r a t e d by n u m e r o u s s u b c i r c u l a r pores. A r m s are each c o m p o s e d of up to six s m o o t h , d i s t i n c t l y r o u n d e d c h a m b e r s b e a r i n g r a t h e r few subcircular pores of differing sizes. S t r u c t u r e s b e t w e e n c h a m b e r s are distinct. A r m s e x p a n d o n l y slightly distally usually e n d i n g w i t h a c o m p l e t e c h a m b e r , b u t s o m e t i m e s t e r m i n a t i n g in a s p o n g y m e s h w o r k w h i c h tapers distally. P a t a g i u m m a y or m a y n o t be p r e s e n t . Small t h o r n like p r o j e c t i o n s a l o n g shell m a r g i n s are o f t e n p r e s e n t , i n d i c a t i v e o f an i n c i p i e n t p a t a g i u m . Dimensions: T o t a l shell l e n g t h u p t o 285 t~m; maxim u m b r e a d t h o f u n b r a n c h e d a r m 4 0 - - 6 5 urn. Remarks: T. straussii is d e s c r i b e d by Haeckel as h a v i n g f o u r simple arms: t w o p r i n c i p a l arms as in t h e species here d e s c r i b e d a n d t w o smaller lateral arms. H a e c k e l ' s f o r m also has m o r e c h a m b e r s or j o i n t s o n each a r m t h a n t h e species f o u n d by us in I n d i a n O c e a n sediments. R e n z ( 1 9 7 4 a n d 1 9 7 6 ) used the species n a m e T. straussii for a f o r m similar to t h a t here described, b u t n o t e d ( 1 9 7 4 ) t h a t t h e cross arms were " r u d i m e n t a r y or c o m p l e t e l y l a c k i n g " . No specim e n w i t h f o u r a r m s was f o u n d in t h e p r e s e n t s t u d y , b u t t h e y have b e e n observed, rarely, by o n e o f us (C.N.) in N o r t h Pacific s e d i m e n t s . It is t h e a u t h o r s ' o p i n i o n t h a t H a e c k e l ' s s p e c i m e n was s i m p l y an unusually c o m p l e t e e x a m p l e of t h e r a t h e r c o m m o n spe-

cies f o u n d by us in t h e I n d i a n O c e a n ( a n d w e v i o u s l y in the N o r t h Pacific) a n d t h a t t h e lateral arms are n o t t a x o n o m i c a l l y i m p o r t a n t . T h e species might, there-fore, be m o r e p r o p e r l y placed in t h e genus Amphirhopalum. A few of o u r s p e c i m e n s are similar ~o A. virchowii, suggesting a r e l a t i o n s h i p b e t w e e n the two species. G e n u s Trigonastrum Haeekel 1887

Trigonastrum sp. (Plate II, 6; Plate iV, 1 6 , ] 7 ) . ?Trigonastrum regulare Haeckel, ] 887, p: 539, pl. 43, fig. 16; D u m i t r i c a , 1973, p. 835~ p l !0, figs. 1--4, pl. 11, figs. 1, 3, 5, 8. Description: T h e s p e c i m e n s e n c o u n t e r e d m the. p r e s e n t s t u d y are similar in m a n y respects ~o those d e s c r i b e d by D u m i t r i c a ( 1 9 7 3 ) . However, c o m p l e t e s p e c i m e n s are very rare a n d usually o n l y t h e c e n t r a l s t r u c t u r e a n d p r o x i m a l parts of the arms (Plate IV, 17) were observed. No s p e c i m e n with a p a t a g i u m was observed, whereas D u m i t r i c a n o t e d a p a t a g i u m on a l m o s t all of his M e d i t e r r a n e a n s p e c i m e n s : T h e presence or a b s e n c e of a p a t a g i u m has previously been f o u n d (Nigrini, 1 9 6 7 ) t o be t a x o n o m i c a l l y u n i m p o r t a n t , b u t it is i n t e r e s t i n g in this case to n o t e t h a t alm o s t all s p e c i m e n s in o n e area have a p a t a g i u m while a l m o s t all s p e c i m e n s in a n o t h e r area do noL F o r the t i m e b e i n g we have c h o s e n to r e t a i n t h e generic n a m e Trigonastrum for t h e s p e c i m e n s f o u n d in Indian O c e a n sediments. However, a t a x o n o m i c revision of these f o r m s w o u l d p r o b a b l y require t h a t Trigonastrum be m a d e a j u n i o r s y n o n y m o f Chitonastrum Haecket 1881. Dimensions: R a d i u s o f arms 6 5 - - 1 4 5 ~rn. M a x i m u m b r e a d t h o f arms 6 5 - - 1 0 5 urn. F o r fully d e v e l o p e d s p e c i m e n radius is 160 urn, b r e a d t h 2 1 0 urn. G e n u s Spongobrachium Haeckel 1881

Spongobrachium sp. (Plate II, 12; Plate V, 3)~ Description: Shell c o m p o s e d o f a flat, l o z e n g e - s h a p e d s p o n g y m e s h w o r k with a c e n t r a l s t r u c t u r e of 2--.-5 c o n c e n t r i c spheres or o b l a t e spheroids. Usually t w o " a r m s " of d e n s e r m e s h w o r k can be seen along the long axis of t h e shell. T h e e x t r e m i t i e s of these a r m s are d e n s e r still. O f t e n t h e p e r i p h e r y of tho shell appears d e n s e r t h a n t h e c e n t r a l p o r t i o n . Dimensions: T o t a l shell l e n g t h 2 5 0 - - 3 5 5 ~ m / u s u a l l y 2 5 0 - - 3 0 5 urn); m a x i m u m b r e a d t h 1 2 0 - - 2 6 5 u m (usually 1 2 0 - - 1 8 5 urn). Remarks: No specific n a m e has been given t~o this species because, as Riedel a n d S a n f i l i p p o ( 1 9 7 8 , pl. 73) have p o i n t e d out, t h e r e are several p o o r l y unders t o o d f o r m s of this general t y p e w h i c h a p p a r e n t l y have s t r a t i g r a p h i c as well as geographic significance. T h e f o r m d e s c r i b e d h e r e i n a p p e a r s to be the same as t h a t i l l u s t r a t e d by R e n z ( 1 9 7 4 , pl. 15, fig. 10) a n d

149

PLATE V (× 275) 1. Amphirhopalum cf. Tessarastum straussii Haeckel, A I I 15-735HC, X20/2. 2. Amphirhopalum cf. Tessarastrum straussii Haeckel, LSDA l 1 9 G , D33/1. 3. Spongobrachium sp., A I I 15-766HC, J27/3. 4. Pterocorys sabae (Ehrenberg), ANTP 142PG, 015/2. 5. Pterocorys sabae (Ehrenberg), LSDA 12G, M32/2.

150

called by her Spongobrachium sp. aff. S. ellipticum Haecket (1862, pl. 28, fig. 2). FAMILY PTEROCORYTHIDAE Haeckel emend. Riedel 1967 emend. Moore 1972

1881

Genus Pterocorys Haeckel 1881 Pterocorys sabae (Ehrenberg) (Plate IV, 2; Plate V, 4,5). Pterocanium sabae Ehrenberg, 1972a, p. 319, 1872b, p. 299, pl. 10, fig. 17, Pterocorys sabae (Ehrenberg) Haeckel, 1887, p. 1317. Description: Shell conical to ovate, quite smooth and rather thin-walled. Cephalis trilocular, the two secondary lobes beneath and somewhat lateral to the larger primary lobe; numerous subcircular pores; cephalis rather heavier than rest of shell. Stout three-bladed apical horn up to twice as long as cephalis. Collar stricture distinct. Thorax basically conical, but shape strongly influenced by three strong ribs which project as short wings about halfway along thoracic length. Pores subcircular, longitudinally aligned. Pores immediately adjacent to cephalis often enlarged. Lumbar stricture distinct. Abdomen broader than thorax, but with similar pores in more complete specimens. However, abdomen usually rudimentary and may have irregular pore arrangement. Termination always ragged. In high latitudes abdomen rarely present. Dimensions: Length of cephalis and thorax 75--105 urn; of abdomen up to 127 urn, Maximum breadth of thorax 75--92 urn; of abdomen up to 127 urn. Remarks: This species differs from P. hertwigii by the absence of longitudinal ridges, and from P. zancleus by being generally larger with larger, more irregular pores and pore alignment. Acknowledgments C o r e s a m p l e s f o r this s t u d y w e r e p r o v i d e d t h r o u g h t h e a s s i s t a n c e o f W. R i e d e l a n d T. Walsh ( S c r i p p s I n s t i t u t i o n o f O c e a n o g r a p h y ) ; F. M c C o y , D. C o o k e , a n d K. T h o m p s o n (Lamont-Doherty Geological Observatory); a n d J. B r o d a , H. F a r m e r a n d D. K e i t h ( W o o d s Hole Oceanographic Institution). Curatorial services a t t h e s e s a m p l e r e p o s i t o r i e s are supported through contracts from the Office of Naval R e s e a r c h a n d g r a n t s f r o m t h e N a t i o n a l Science Foundation (Submarine Geology and G e o p h y s i c s P r o g r a m ) . This p r o j e c t is supp o r t e d b y N . S . F . G r a n t O C E 7 6 - 2 0 1 5 4 . We

t h a n k R. G r o m a n , T. S c h u l t z , a n d A. Nigrini f o r a s s i s t a n c e in m o d i f y i n g t h e R E G R O U P p r o g r a m for c o m p a t i b i l i t y with the Woods H o l e Sigma-7 c o m p u t e r . T h e K e n n e c o t t Develo p m e n t Center p r o v i d e d facilities for p h o t o microscopy. G. L o h m a n n , T. M o o r e , a n d B. Corliss c r i t i c a l l y r e v i e w e d t h e m a n u s c r i p t . C o n t r i b u t i o n No. 4 4 4 1 o f t h e W o o d s H o l e Oceanographic Institution. References B6, A.W.H. and Hutson, W,H., 1977. Ecology of" planktonic foraminifera and biogeographic patterns of life and fossil assemblages in the Indian Ocean. Micropaleontology, 23: 369--41,1-. Campbell, A.S., 1954. Subclass Radiolaria. In: R,C. Moore (Editor), Treatise on Invertebrate Paleontology. Protista 3. University of Kansas, Lawrence, Kansas, pp. Dll--D163. Caulet, J.-P., 1977. La siliee biog6ne dans tes s6diments n6og6nes et quaternaires de l'oc6an Indien austral. Bull. Soc. G6ol. Fr., 19: 1021--1032: Caulet, J.-P., 1978. S6dimentation biosiliceuse n6og6ne et quaternaire dans l'oc6an Indien. 13~!1.Soc. G6ol. Ft., 20: 577--583. Defant, A., 1961. Physical Oceanography. Pergamor; Press, New York, N.Y., 598 pp. Dow, R.L., 1978. Radiolarian distributicm and the late Pleistocene history of the southeastern Indian Ocean. Mar. Micropaleontok, 3: 203- 227 Dumitrica, P., 1973. Cretaceous and Quaternary radiolaria in deep sea sediments from the: northeast Atlantic Ocean and Mediterranean Sea. DSDP Leg 13. In: W.B.F. Ryan, K.J. Hsii et ak, {nitiai Reports of the Deep Sea Drilling Projeci,, i3. U.S. Government Printing Office, Washingto~n I).C. pp. 829--901. Ehrenberg, C.G., 1872a. Mikrogeologische Studien ais Zusammenfassung seiner Beobachtungen des kleinsten Lebens der Meeres-Tiefgrunde aller Zonen und dessen geologischen Einfluss. K. Preuss. Akad Wiss. Monatsber., 1872: 265--322. Ehrenberg, C.G,, 1872b. Mikrogeologische Studien fiber das kleinste Leben der Meeres-Tiefgrunde aller Zonen und dessen geologischen Einfluss. K. Akad. Wiss. Berlin, Abh., 1872: 131t 1 3 9 9 (pls. 1--52). Fager, E,W., 1957. Determination and analysis o1" recurrent groups. Ecology, 38: 586---595. Fager, E.W. and McGowan, J.A., 11963. Zooplankton species groups in the North Pacific. Science, 140: 453--460. Goll, R.M. and Bj6rklund, K.R., 1971. Radiotaria in surface sediments of the North Atlantic Oceam Micropaleontology, 17 : 434--,15:1

151

Goll, R.M. and Bj~brklund, K.R., 1974. Radiolaria in surface sediments of the South Atlantic. Micropaleontology, 20: 38--75. Haeckel, E., 1862. Die Radiolarien, Eine Monographie. 572 pp. (pls. 1--35). Haeckel, E., 1887. Report on the radiolaria collected by H.M.S. CHALLENGER during the years 1873-1876. "Chall." Rep. Zool., 1803 pp. (pls. 1--140). Hays, J.D., 1965. Radiolaria and Late Tertiary and Quaternary history of Antarctic Seas. Am. Geophys. Union Antarc. Res. Ser. 5, Biol. Antarc. Seas, 2 : 1 2 5 - - 1 8 4 (pls. 1--3). Hutson, W.H. and Prell, W.L., 1980. A paleoecological transfer function, FI-2, for Indian Ocean planktonic foraminifera. J. Paleontol, 54: 381-399. Imbrie, J. and Kipp, N.G., 1971. A new micropaleontological method for a quantitative paleoclimatology: application to a late Pleistocene Caribbean core. In: K.K. Turekian (Editor), The Late Cenozoic Glacial Ages. Yale University Press, New Haven, Conn., pp. 71--181. Jacobs, S.S. and Georgi, D.T., 1977. Observations on the southwest Indian/Antarctic Ocean. Deep-Sea Res. (supplement), 24: 43--84. Johnson, D.A. and Damuth, J.E., 1979. Deep thermohaline flow and current-controlled sedimentation in the Amirante Passage, Western Indian Ocean. Mar. Geol., 33: 1--44. Johnson, D.A. and Nigrini, C., in prep. Late Pleistocene radiolarian biogeography in the western Indian Ocean. Joust, A.P., 1977. Atlas of Microorganisms in Bottom Sediments of the Ocean: Diatoms, Radiolaria, Silicofiagellates and Coccoliths. Publishing House Nauka, Moscow, 196 pp. (160 pls.) Knoll, A. and Johnson, D., 1975. Late Pleistocene evolution of the collosphaerid radiolarian Buccinosphaera invaginata Haeckel. Micropaleontology, 21 : 60--68. Lisitzin, A.P., 1967. Basic relationships in distribution of modern siliceous sediments and their connection with climatic zonation. Int. Geol. Rev., 9: 631--652. Lisitzin, A.P., 1972. Sedimentation in the world ocean. Soc. Econ. Paleontol. Mineral. Spec. Pub., 1 7 : 2 1 8 pp. Lisitzin, A.P., Belayayev, Y.I., Bogdanov, Y.A. and Bogoyavlenskiy, A.N., 1967. Distribution relationships and forms of silicon suspended in waters of the world ocean. Int. Geol. Rev., 9: 604--623. Lozano, J.A., 1974. Antarctic Sedimentary, Faunal and Sea Surface Temperature Responses During the Last 230,000 Years with Emphasis on Comparison Between 18,000 Years Ago and Today. Dissertation, Columbia University, New York, N.Y., 4OO pp.

Lozano, J.A. and Hays, J.D., 1976. Relationship of radiolarian assemblages to sediment types and physical oceanography in the Atlantic and western Indian Ocean sectors of the Antarctic Ocean. Geol. Soc. Am. Mere., 145: 303--336. Molina-Cruz, A., 1977. Radiolarian assemblages and their relationship to the oceanography of the subtropical southeastern Pacific. Mar. Micropaleontol., 2: 315--352. Moore, T.C., Jr., 1973. Late Pleistocene--Holocene oceanographic changes in the northeastern Pacific. Quaternary Res., 3: 99--109. Moore, T.C., Jr., 1978. The distribution of radiolarian assemblages in the modern and ice-age Pacific. Mar. Micropaleontol., 3: 229--266. Morley, J., 1977. Upper Pleistocene Climatic Variations in the South Atlantic Derived from a Quantitative Radiolarian Analysis: Accent on the Last 18,000 Years. Dissertation, Columbia University, New York, N.Y., 282 pp. Muller, J., 1855. Ueber Sphaerozoum und Thalassicolla. K. Preuss. Akad. Wiss. Monatsber., 1855: 229--253. Muller, J., 1858. Ueber die Thalassicollen, Polycystinen und Acanthometren des Mittelmeeres. K. Akad. Wiss., Berlin, Abh., 1 8 5 5 : 6 2 pp. (pls. 1--11). Nigrini, C., 1967. Radiolaria in pelagic sediments from the Indian and Atlantic Oceans. Bull. Scripps Inst. Oceanogr., 1 1 : 1 - - 1 0 6 (pls. 1--9). Nigrini, C., 1968. Radiolaria from eastern tropical Pacific sediments. Micropaleontology, 14: 51--63. Nigrini, C., 1970. Radiolarian assemblages in the North Pacific and their application to a study of Quaternary sediments in core V20-130. Geol. Soc. Am. Mere., 126: 139--183. Nigrini, C., 1971. Radiolarian zones in the Quaternary of the equatorial Pacific Ocean. In: B.M. Funnell and W.R. Riedel (Editors), The Micropaleontology of Oceans. Cambridge University Press, Cambridge, pp. 443--461. Nigrini, C., 1974. Cenozoic Radiolaria from the Arabian Sea, DSDP Leg 23. In: T.A. Davies, B.P. Luyendyk et al., Initial Reports of the Deep Sea Drilling Project, 26. U.S. Government Printing Office, Washington, D.C., pp. 1051--1121. Nigrini, C., 1977. Tropical Cenozoic Artostrobiidae (Radiolaria). Micropaleontology, 23: 241--269 (pls. 1--4). Nigrini, C. and Moore, T.C., Jr., 1979. A guide to modern Radiolaria. Cushman Found. Foraminiferal Res., Spec. Publ., No. 16. Petrushevskaya, M.G., 1965. Osobennosti konstruktsii skeleta radiolyarii Botryoidae (otr. Nassellaria). Tr. Zool. Inst., Akad. Nauk S.S.S.R., 35: 79--118. Petrushevskaya, M.G., 1967. Radiolyarii otryadov Spumellaria i Nassellaria antarkticheskoi ovlasti

152

(po materialam Sovetskoi antarkticheskoi ekspeditsii) [Antarctic spummeline and nasseline radiolarians (in collections of the Soviet Antarctic Expedition)]. In: E.N. Pavlovskii (Editor), Issledovaniya Fauny Morel, 3(12). Nauka, Leningrad, pp. 3--186 (figs. 1--102). Petrushevskaya, M.G., 1971. Radiolaria in the plankton and Recent sediments from the Indian Ocean and Antarctic. In: B.M. Funnell and W.R. Riedel (Editors), The Micropaleontology of Oceans. Cambridge University Press, Cambridge, pp. 319 ...... 329. ?etrushevskaya, M.G., 1972a. Biostratigrafiya glubokovodnykh chetvertichnykh osadkov po dannym radiolyarievogo analyza. [Biostratigraphy of deep-sea Quaternary sediments as based on the data of radiolarian analysis. ] Okeanologiya, 12( 1 ): 71--86. Petrushevskaya, M.G., 1972b. Nyekotoriye voprosi paleogeografii po materialam radiolyarievogo analiza glubokovodnikh donnikh otlozhenii [Some questions on paleogeography according to the materials of radiolarian analysis of deep water bottom sediments]. Okeanologiya, 12(4): 640-652. Petrushevskaya, M.G., 1973. Polycystine radiolarians in the bottom sediments of the Indian Ocean as indicators of hydrogeological conditions. In: Plankton i organicheskii mir pelagiali v isotorii zemli, Vsesoyoznogo orgena Lenina nauchnoissledovatelskii geologicheskii institut. VSEGEI, Leningrad, pp. 44--45. Popofsky, A., 1917. Die Collosphaeriden der Deutschen Sfidpolar-Expedition 1901--1903. Mit Nachtrag zu den Spumellarien und der Nassellarien. Dtsch. Sfidpolar-Exped., 16 (Zool. 8)(3): 235--278 (pls. 13--17). Prell, W.L., 1978. Variability of monsoonal upwelling in the western Arabian Sea: Holocene intensification and glacial reduction. Geol. Soc. Am., Abst. Progr., 10: 474. Prell, W.L., Hutson, W.H. and Williams, D.F., 1979. The Subtropical Convergence and late Quaternary circulation in the southern Indian Ocean. Mar. Micropaleontol., 4: 225--234. Renz, G,W., 1974. Radiolaria from Leg 27 of the Deep Sea Drilling Project. In: J.J. Veevers, J.R. Heirtzler et al., Initial Reports of the Deep Sea Drilling Project, 27. U.S. Government Printing Office, Washington, D.C., pp. 769--841, Renz, G.W., 1976. The distribution and ecology of radiolaria in the central Pacific -- plankton and surface s0diments. Bull. Scripps Inst. Oceanogr., 2 2 : 2 6 7 pp.

Riedel, W.R., 1958. Radiolaria in Antarctic sediments. B.A.N.Z. Antarc. Res. Exped. Rep. Ser. B, 6(pt. 10): 217--255 (pls. 1--4). Riedel, W.R., 1967. Protozoa, class Actinopoda. In: The Fossil Record, A Symposium with D,~cumenration. Geol. Soc. Lond. Publ., pp. 291--298. Riedel, W.R. and Sanfilippo, A., 1977. Cenozoic Radiolaria. In: A.T.S. Ramsay (Editor'), Oceanic Micropaleontology. Academic Press, New York. N.Y., pp. 847--912. Riedel, W.R. and Sanfilippo, A., 1978. Stratigraphy and evolution of tropical Cenozoic radiolarians. Micropaleontology, 23(1): 61--96 (pls. 1--10). Robertson, J., 1975. Glacial to Interglacial Oceanographic Changes in the Northwest Pacific, Including a Continuous Record of the Last 400,000 Years. Dissertation, Columbia University, New York. N.Y., 355 pp. Sachs, H.M., 1973a. Quantitative Radiolarian-Based Paleo-oceanography in Late Pleistocene Subarctic Pacific Sediments. Dissertation, Brown University. Providence, R.I. Sachs, H.M., 1973b. North Pacific radiolarian assemblages and their relationship to oceanographic parameters. Quaternary Res., 3: 73--88. Sancetta, C., 1978. Neogene Pacific microfo,ssils and paleo-oceanography. Mar. Micropaleontol., 3: 347--376. Strelkov, A.S. and Reshetnyak, V.V., 1971. Kotonialnie radiolarii spumellaria mirovogo okeana. In: Radiolarii mirovogo okeana po materialam sovetskikh ekspeditskii. Issled. Fauni Morel, Leningrad, Nauka, 9(17): 295--369 (pls. l 10). Swallow, J.C. and Bruce, J.G., 1966. Current measurements off the Somali coast during the southwest monsoon of 1964. Deep-Sea Res., 13: 861--888. Warren, B.A., 1974. Deep flow in the Madagascar and Mascarene Basins. Deep-Sea Res., 21: l - 2 . Warren, B.A., 1978. Bottom water transport through the Southwest Indian Ridge. Deep-Sea Res., 25: 315--321. Warren, B., Stommel, H. and Swallow, J.(L. 1966. Water masses and patterns of flow in the Somali Basin during the southwest monsoon of 1964. Deep-Sea Res., 13: 825--860. Wyrtki, K., 1971. Oceanographic Atlas of the International Indian Ocean Expedition. National Science Foundation, Washington, D.C., 531 pp. Wyrtki, K., 1973. Physical oceanography of the Indian Ocean. In: B. Zeitzschel (Editor), The Biology of the Indian Ocean. Springer-Verlag, New York, N.Y., pp. 18--36. Zeitzschel, B., 1973. The Biology of the Indian Ocean. Springer-Verlag, New York, 549 pp.