- Email: [email protected]
Calcium sulfate hemihydrate (bassanite) statoliths in the cubozoan Carybdea sp.
ARTICLE IN PRESS
Zoologischer Anzeiger 245 (2006) 13–17 www.elsevier.de/jcz
Calcium sulfate hemihydrate (bassanite) statoliths in the cubozoan Carybdea sp. Henry Tiemanna,, Ilka So¨tjea, Alexander Beckerb, Gerhard Jarmsa, Matthias Eppleb a
Biocenter Grindel, University of Hamburg, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany Inorganic Chemistry, University of Duisburg-Essen, Universitaetsstraße 5-7, D-45117 Essen, Germany
b
Received 15 July 2005; received in revised form 14 December 2005; accepted 2 March 2006 Corresponding editor: M.V. Sørensen
Abstract The chemistry and physical structure of statoliths of young cubozoan medusae (Carybdea sp.) were examined by X-ray spectroscopy (EDX) and X-ray powder diffractometry (XRD). These concretions, associated with sensory receptors, were found to consist of bassanite (calcium sulfate hemihydrate), a dense but hygroscopic biomineral. Bassanite occurs in a cluster of radially oriented crystals in a druse, which contains perfect hexagonal crystals. This discovery provides evidence that the Rhopaliophora (Scyphozoa and Cubozoa) originated from an ancestor having statoliths of bassanite. r 2006 Elsevier GmbH. All rights reserved. Keywords: Rhopaliophora; Biomineralisation; Calcium sulfate; X-ray diffraction; Phylogeny
1. Introduction The Cnidaria are divided in four monophyletic classes (Schuchert 1993) and recently Marques and Collins (2004) have published a revised phylogenetic tree of the cnidaria, and introduce an additional class, the staurozoa. Only three classes have a medusa stage. These three classes can be grouped as Tesserazoa because of several apomorphic features of the polyp stage (SalviniPlawen 1978). The development of the medusae in the classes Scyphozoa and Hydrozoa are independent differentiations whereas the Cubozoa are assumed to be derived from the Scyphozoa. Ax (1995) merged the Corresponding author. Tel.: +49 040 42838 2784; fax: +49 040 42838 3937. E-mail address: [email protected] (H. Tiemann).
0044-5231/$ - see front matter r 2006 Elsevier GmbH. All rights reserved. doi:10.1016/j.jcz.2006.03.001
sister groups Scyphozoa and Cubozoa into the taxon Rhopaliophora. The marginal sense organs of the Hydrozoa and Rhopaliophora have a different developmental origin (Werner 1984; Ax 1995). The statolith material of hydrozoan genera (Obelia, Lovenella, Phialella and Mitrocomella; Hydroida; Aglantha digitale; Trachylida) consists of calcium magnesium phosphate (Singla 1975; Chapman 1985) whereas that of a number of scyphozoan medusa (Aurelia aurita, Cyanea capillata, C. lamarckii – Semaeostomeae; Periphylla periphylla – coronata; Rhizostoma octopus – Rhizostomeae) is the unusual biomineral bassanite (Tiemann et al. 2002; Becker et al. 2005). The statolith material of the cubozoan medusa Carybdea rastoni (Ueno et al. 1995, 1997) and Chiropsalmus sp.(Chapman, 1985) was described as gypsum (CaSO4 2H2O) as reported by some authors in Scyphomedusae (Spangenberg and Beck 1968; Chapman
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H. Tiemann et al. / Zoologischer Anzeiger 245 (2006) 13–17
1985; Pollmanns and Hu¨ndgen 1981). The structure of cubozoan statocysts appears to differ from that of scyphozoans in consisting of a sphere rather than a cluster of crystals (Ueno et al. 1995; Becker et al. 2005). Nevertheless the inorganic mineral phase could be the same. Modern methods now make it possible to examine the mineral of the crystals of cubozoans in more detail and with higher accuracy. This research was undertaken to determine whether calcium sulfate hemihydrate (bassanite) is also present in the statoliths of cubozoan medusae.
2. Material and methods Cubozoan polyps were discovered in a salt-water tank at the Troparium of the Hagenbecks Tierpark Zoo in Hamburg during 1998. They were found together with Scyphistomae of the coronate scyphozoan Nausithoe hagenbecki Jarms, 2001. Cultures were maintained at 27 1C, and at that temperature asexual propagation occurred by fission of creeping polyps. Each adult polyp underwent metamorphosis into a single medusa. The still undescribed species is to classify as Carybdeidae because of its single medusa tentacles on an own pedalium each (Fig. 1). The polyp with a single stenotele at the tip of each tentacle and the characteristic creeping polyps display typical characters of the genus Carybdea. About 60 young medusae between 0.5 and 0.6 mm diameter were preserved in 80% ethanol a few days after metamorphosis. Previous control experiments with different methods for fixation in ethanol or drying over solid gypsum or over solid bassanite showed that fixation in 80% ethanol neither leads to a dehydration of gypsum nor to a rehydration of bassanite, accordingly preparation artefacts could be discounted (Tiemann et al. 2002). The length of the crystals could not be measured by scanning electron microscope (SEM), because of their orientation in the statocyst. Therefore a special method for the light microscopic examination was developed. The whole rhopalium was mounted in water-free glycerol with 0.7% potassium hydroxide on microscopic slides to mazerate the organic tissue and conserve the hygroscopic crystal material. The statocyst becomes translucent and can be spread easily. One medusa was cultivated for 3 weeks and used for the drawing (Fig. 1). For analysis by SEM and X-ray spectroscopy (EDX) the medusae were dried in pure ethanol, placed on aluminum stubs and sputter-coated with graphite. The analysis was carried out with an SEM type Leo 1525, EDX Analysis System Falcon HX 0299. For high-resolution synchrotron X-ray powder diffractometry (XRD), the intact statocysts were used (i.e. with the crystals inside the tissue; not ground). The
experiment was carried out in transmission geometry at beamline B2 at HASYLAB/DESY, Hamburg, Ger( many, with an X-ray wavelength of l ¼ 1.1–1.2 A, depending on the experiment (Becker et al. 2005). Different samples were measured multiple times.
3. Results The statoliths (ca. 20 mm width and 40–50 mm length) of young medusae of Carybdea sp. occurred as conspicuous structures inside the complex rhopalia beside the eyes (Figs. 1–3). Under light microscopy they appear as a cluster of crystals in the rhopalium, distal to the eyes (Fig. 4). The cluster of crystals is fused centrally, which becomes obvious during the preparation. Hexagonal prismatic crystals with well-grown faces and edges are recognizable by SEM (Fig. 3). The EDX spectrum revealed that the main components were calcium, sulfur and oxygen, as well as carbon (from sputtering) and small amounts of sodium, potassium and phosphorus (Fig. 5). A synchrotron X-ray powder diffractogram of statocysts of Carybdea sp. is shown in Fig. 6. For better
Fig. 1. Carybdea sp.: medusa, drawing after life observation, scale bar 3 mm, b – bell, m – mouth, rh – statolith including statocyst, t – tentacle.
ARTICLE IN PRESS H. Tiemann et al. / Zoologischer Anzeiger 245 (2006) 13–17
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Fig. 2. Carybdea sp.: subumbrellar view, SEM after ethanol drying, scale bar 20 mm. m – mouth, st – statolith.
Fig. 4. Carybdea sp.: rhopalium, drawing after embedding in water-free glycerol, scale bar 100 mm. ac I – accessory eye I, ac II – accessory eye II, dle – distal lense eye, ple – proximal lense eye, sk – stalk, skc – stalk canal, st – statolith.
Fig. 5. Carybdea sp.: energy-dispersive X-ray spectrum of the statoliths within the rhopalia. Fig. 3. Carybdea sp.: crystals of the statolith, SEM after ethanol drying, scale bar 10 mm. ci – cilia, st – statolith, sc – statocyst.
comparison with standard laboratory set-ups, the data were converted to Cu Ka1 radiation wavelength ( Only peaks which could be assigned (l ¼ 1.54056 A). to the mineral phase bassanite (CaSO4 1/2 H2O) (Abriel and Nesper 1993) were found (14.5, 25.5, 29.7, 31.7, 49.1, 54.0 and 54.81 2Y). The Bragg reflection positions of bassanite are indicated in Fig. 6. No other diffraction peaks were visible, i.e. crystalline gypsum (dihydrate) can be excluded. The background between 10 and 301 2Y results from the high content of amorphous
biological material in the sample (Fig. 6). The small amount of material necessitated the use of high-intensity synchrotron powder diffraction. Still, the signal-to-noise ratio is only moderate. Notably, this analysis would have been impossible with a conventional X-ray diffractometer equipped with an X-ray tube.
4. Discussion Large Cubozoa have solid ellipsoid statoliths (one per statocyst) with daily growth rings (Ueno et al. 1995, 1997).
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H. Tiemann et al. / Zoologischer Anzeiger 245 (2006) 13–17
Fig. 6. Carybdea sp.: X-ray powder diffractogram of the crystals within the rhopalia. The computed positions for calcium sulfate hemihydrate are indicated as vertical bars.
The appearance of this massive statolith is decidedly different from the collection of single crystals in the rhopalia of the scyphozoans. We examined very young Carybdea sp. medusae and found many hexagonal crystals consisting of bassanite within one statocyst with a structure which is quite similar to the crystals of the coronate medusa Periphylla periphylla and other scyphozoan medusae (Tiemann et al. 2002; Becker et al. 2005). From the almost perfect shape of the crystals it can be concluded that they contain only one mineral in the form of a single crystal. X-ray diffraction showed unequivocally that the material is the water-deficient modification of calcium sulfate and certainly not gypsum (i.e. the dihydrate of calcium sulfate). The small amounts of sodium, potassium and phosphate that were detected can be related to cellular material, while the carbon peak is also caused by the sputtering process. In the young medusae examined here, a cluster of crystals develops at first, similar to P. periphylla. The crystals grow together during further development and form a radiating star before they merge into a solid mass. The concentric layers described by Ueno et al. (1995) in older cubozoan medusae statoliths must appear by the further uptake of calcium sulfate hemihydrate during growth. The structure of the statoliths of the young medusae is therefore highly similar to these structures in Scyphozoa as to size, mineralogy and prismatic appearance. We found a similar radial arrangement of the crystals (not fused) in the statolith of A. aurita by synchrotron radiation-based microcomputer tomography (SRmCT) (Becker et al. 2005). The anatomy of the rhopalia in Scyphozoa and Cubozoa was described by Russel (1970) and Werner (1984). The location of the eyes on the rhopalium and the distal located statocyst is
homologous in both groups. The anatomy of early statocyst-stages is comparable in coronata (Tiemann et al. 2002), Semeaostomeae, Rhizostomeae (Becker et al. 2005) and Cubozoa concerning their content of isolated prismatic crystals. The statocyst of scyphozoans stays on this stage during their whole life. The only development is the growth in size and number of the crystals. Contrarily the cubozoan statolith further develops into a solid ellipsoid. We interpret the appearance of isolated prismatic crystals at the beginning of the statolith development as a plesiomorphic feature of the class of Cubozoa. The subsequent development of a spherical statolith composed of thin layers is an autapomorphy. Schuchert (1993) considers the Scyphozoa and the Cubozoa as sister groups because of the existence of rhopalia, which derive from polyp tentacles. Marques and Collins (2004) created the new taxon Staurozoa, postulated as sister group of the Cubozoa and both groups together as sister group of the other scyphozoans. The appearance of the biomineral calcium sulfate hemihydrate, or bassanite, in statocyst of Cubozoa and Scyphozoa confirms their close relationship. The formation and use of the unusual (and within the animal kingdom unique) hygroscopical biomineral bassanite is an ancient attribute of both groups, which had to have a pelagic generation already at that time. It is possibly preserved because of its high density compared to dihydrate (gypsum).
Acknowledgements We are grateful to HASYLAB at DESY, Hamburg, for generous allocation of beamtime and to Drs. C. Baehtz and M. Knapp for experimental assistance. We thank Dr. D. Keyser and R. Walter (Hamburg) for assistance with electron microscopy.
References Abriel, W., Nesper, R., 1993. Bestimmung der Kristallstruktur von CaSO4(H2O)0.5 mit Ro¨ntgenbeugungsmethoden und mit Potentialprofil-Rechnungen. Z. Kristallogr. 205, 99–113. Ax, P., 1995. Das System der Metazoa I. Ein Lehrbuch der phylogenetischen Systematik. Fischer, Stuttgart. Becker, A., So¨tje, I., Paulmann, C., Beckmann, F., Donath, T., Boese, R., Prymak, O., Tiemann, H., Epple, M., 2005. Calcium sulfate hemihydrate is the inorganic mineral in statoliths of Scyphozoan medusae (Cnidaria). Dalton Trans. 1, 1545–1550. Chapman, D.M., 1985. X-ray microanalysis of selected coelenterate statoliths. J. Mar. Biol. Assess. UK 65, 617–627.
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Marques, A.C., Collins, A.G., 2004. Cladistic analysis of Medusozoa and Cnidarian evolution. Invertebr. Biol. 123 (1), 23–42. Pollmanns, D., Hu¨ndgen, M., 1981. Licht- und elektronenmikroskopische Untersuchung der Rhopalien von Aurelia aurita (Scyphozoa, Semaeostomae). Zool. Jb. Anat. 105, 508–525. Russel, F.S., 1970. The medusae of the British Isles. II. Pelagic Scyphozoa with a supplement to the first volume on Hydromedusae. Cambridge University Press, Cambridge, pp. 1–284. Salvini-Plawen, L., 1978. On the origin and evolution of the lower metazoa. Z. Zool. Syst. Evol. Forsch. 16, 40–88. Schuchert, P., 1993. Phylogenetic analysis of the Cnidaria. Z. Zool. Syst. Evol. Forsch. 31, 161–173. Singla, C.L., 1975. Statocysts of Hydromedusae. Cell Tissue Res. 158, 391–407.
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Spangenberg, D., Beck, C.W., 1968. Calcium sulfate dihydrate statoliths in Aurelia. Trans. Am. Microsc. Soc. 87 (3), 329–335. Tiemann, H., So¨tje, I., Jarms, G., Paulmann, C., Epple, M., Hasse, B., 2002. Calcium sulfate hemihydrate in statoliths of deep-sea medusae. Dalton Trans., 1266–1268. Ueno, S., Imai, C., Mitsutani, A., 1995. Fine growth rings found in statolith of a cubomedusa Carybdea rastoni. J. Plankton Res. 17 (6), 1381–1384. Ueno, S., Imai, C., Mitsutani, A., 1997. Statolith formation and increment in Carybdea rastoni Haacke, 1886 (Scyphozoa: Cubomedusae): evidence of synchronization with semilunar rhythms. Proceedings of the Sixth International Conference on Coelenterate Biology. Werner, B., 1984. Cnidaria. In: Gruner, H.-E. (Ed.), Lehrbuch der speziellen Zoologie, Vol. 1. Fischer, Jena, pp. 11–305.
Zoologischer Anzeiger 245 (2006) 13–17 www.elsevier.de/jcz
Calcium sulfate hemihydrate (bassanite) statoliths in the cubozoan Carybdea sp. Henry Tiemanna,, Ilka So¨tjea, Alexander Beckerb, Gerhard Jarmsa, Matthias Eppleb a
Biocenter Grindel, University of Hamburg, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany Inorganic Chemistry, University of Duisburg-Essen, Universitaetsstraße 5-7, D-45117 Essen, Germany
b
Received 15 July 2005; received in revised form 14 December 2005; accepted 2 March 2006 Corresponding editor: M.V. Sørensen
Abstract The chemistry and physical structure of statoliths of young cubozoan medusae (Carybdea sp.) were examined by X-ray spectroscopy (EDX) and X-ray powder diffractometry (XRD). These concretions, associated with sensory receptors, were found to consist of bassanite (calcium sulfate hemihydrate), a dense but hygroscopic biomineral. Bassanite occurs in a cluster of radially oriented crystals in a druse, which contains perfect hexagonal crystals. This discovery provides evidence that the Rhopaliophora (Scyphozoa and Cubozoa) originated from an ancestor having statoliths of bassanite. r 2006 Elsevier GmbH. All rights reserved. Keywords: Rhopaliophora; Biomineralisation; Calcium sulfate; X-ray diffraction; Phylogeny
1. Introduction The Cnidaria are divided in four monophyletic classes (Schuchert 1993) and recently Marques and Collins (2004) have published a revised phylogenetic tree of the cnidaria, and introduce an additional class, the staurozoa. Only three classes have a medusa stage. These three classes can be grouped as Tesserazoa because of several apomorphic features of the polyp stage (SalviniPlawen 1978). The development of the medusae in the classes Scyphozoa and Hydrozoa are independent differentiations whereas the Cubozoa are assumed to be derived from the Scyphozoa. Ax (1995) merged the Corresponding author. Tel.: +49 040 42838 2784; fax: +49 040 42838 3937. E-mail address: [email protected] (H. Tiemann).
0044-5231/$ - see front matter r 2006 Elsevier GmbH. All rights reserved. doi:10.1016/j.jcz.2006.03.001
sister groups Scyphozoa and Cubozoa into the taxon Rhopaliophora. The marginal sense organs of the Hydrozoa and Rhopaliophora have a different developmental origin (Werner 1984; Ax 1995). The statolith material of hydrozoan genera (Obelia, Lovenella, Phialella and Mitrocomella; Hydroida; Aglantha digitale; Trachylida) consists of calcium magnesium phosphate (Singla 1975; Chapman 1985) whereas that of a number of scyphozoan medusa (Aurelia aurita, Cyanea capillata, C. lamarckii – Semaeostomeae; Periphylla periphylla – coronata; Rhizostoma octopus – Rhizostomeae) is the unusual biomineral bassanite (Tiemann et al. 2002; Becker et al. 2005). The statolith material of the cubozoan medusa Carybdea rastoni (Ueno et al. 1995, 1997) and Chiropsalmus sp.(Chapman, 1985) was described as gypsum (CaSO4 2H2O) as reported by some authors in Scyphomedusae (Spangenberg and Beck 1968; Chapman
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H. Tiemann et al. / Zoologischer Anzeiger 245 (2006) 13–17
1985; Pollmanns and Hu¨ndgen 1981). The structure of cubozoan statocysts appears to differ from that of scyphozoans in consisting of a sphere rather than a cluster of crystals (Ueno et al. 1995; Becker et al. 2005). Nevertheless the inorganic mineral phase could be the same. Modern methods now make it possible to examine the mineral of the crystals of cubozoans in more detail and with higher accuracy. This research was undertaken to determine whether calcium sulfate hemihydrate (bassanite) is also present in the statoliths of cubozoan medusae.
2. Material and methods Cubozoan polyps were discovered in a salt-water tank at the Troparium of the Hagenbecks Tierpark Zoo in Hamburg during 1998. They were found together with Scyphistomae of the coronate scyphozoan Nausithoe hagenbecki Jarms, 2001. Cultures were maintained at 27 1C, and at that temperature asexual propagation occurred by fission of creeping polyps. Each adult polyp underwent metamorphosis into a single medusa. The still undescribed species is to classify as Carybdeidae because of its single medusa tentacles on an own pedalium each (Fig. 1). The polyp with a single stenotele at the tip of each tentacle and the characteristic creeping polyps display typical characters of the genus Carybdea. About 60 young medusae between 0.5 and 0.6 mm diameter were preserved in 80% ethanol a few days after metamorphosis. Previous control experiments with different methods for fixation in ethanol or drying over solid gypsum or over solid bassanite showed that fixation in 80% ethanol neither leads to a dehydration of gypsum nor to a rehydration of bassanite, accordingly preparation artefacts could be discounted (Tiemann et al. 2002). The length of the crystals could not be measured by scanning electron microscope (SEM), because of their orientation in the statocyst. Therefore a special method for the light microscopic examination was developed. The whole rhopalium was mounted in water-free glycerol with 0.7% potassium hydroxide on microscopic slides to mazerate the organic tissue and conserve the hygroscopic crystal material. The statocyst becomes translucent and can be spread easily. One medusa was cultivated for 3 weeks and used for the drawing (Fig. 1). For analysis by SEM and X-ray spectroscopy (EDX) the medusae were dried in pure ethanol, placed on aluminum stubs and sputter-coated with graphite. The analysis was carried out with an SEM type Leo 1525, EDX Analysis System Falcon HX 0299. For high-resolution synchrotron X-ray powder diffractometry (XRD), the intact statocysts were used (i.e. with the crystals inside the tissue; not ground). The
experiment was carried out in transmission geometry at beamline B2 at HASYLAB/DESY, Hamburg, Ger( many, with an X-ray wavelength of l ¼ 1.1–1.2 A, depending on the experiment (Becker et al. 2005). Different samples were measured multiple times.
3. Results The statoliths (ca. 20 mm width and 40–50 mm length) of young medusae of Carybdea sp. occurred as conspicuous structures inside the complex rhopalia beside the eyes (Figs. 1–3). Under light microscopy they appear as a cluster of crystals in the rhopalium, distal to the eyes (Fig. 4). The cluster of crystals is fused centrally, which becomes obvious during the preparation. Hexagonal prismatic crystals with well-grown faces and edges are recognizable by SEM (Fig. 3). The EDX spectrum revealed that the main components were calcium, sulfur and oxygen, as well as carbon (from sputtering) and small amounts of sodium, potassium and phosphorus (Fig. 5). A synchrotron X-ray powder diffractogram of statocysts of Carybdea sp. is shown in Fig. 6. For better
Fig. 1. Carybdea sp.: medusa, drawing after life observation, scale bar 3 mm, b – bell, m – mouth, rh – statolith including statocyst, t – tentacle.
ARTICLE IN PRESS H. Tiemann et al. / Zoologischer Anzeiger 245 (2006) 13–17
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Fig. 2. Carybdea sp.: subumbrellar view, SEM after ethanol drying, scale bar 20 mm. m – mouth, st – statolith.
Fig. 4. Carybdea sp.: rhopalium, drawing after embedding in water-free glycerol, scale bar 100 mm. ac I – accessory eye I, ac II – accessory eye II, dle – distal lense eye, ple – proximal lense eye, sk – stalk, skc – stalk canal, st – statolith.
Fig. 5. Carybdea sp.: energy-dispersive X-ray spectrum of the statoliths within the rhopalia. Fig. 3. Carybdea sp.: crystals of the statolith, SEM after ethanol drying, scale bar 10 mm. ci – cilia, st – statolith, sc – statocyst.
comparison with standard laboratory set-ups, the data were converted to Cu Ka1 radiation wavelength ( Only peaks which could be assigned (l ¼ 1.54056 A). to the mineral phase bassanite (CaSO4 1/2 H2O) (Abriel and Nesper 1993) were found (14.5, 25.5, 29.7, 31.7, 49.1, 54.0 and 54.81 2Y). The Bragg reflection positions of bassanite are indicated in Fig. 6. No other diffraction peaks were visible, i.e. crystalline gypsum (dihydrate) can be excluded. The background between 10 and 301 2Y results from the high content of amorphous
biological material in the sample (Fig. 6). The small amount of material necessitated the use of high-intensity synchrotron powder diffraction. Still, the signal-to-noise ratio is only moderate. Notably, this analysis would have been impossible with a conventional X-ray diffractometer equipped with an X-ray tube.
4. Discussion Large Cubozoa have solid ellipsoid statoliths (one per statocyst) with daily growth rings (Ueno et al. 1995, 1997).
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H. Tiemann et al. / Zoologischer Anzeiger 245 (2006) 13–17
Fig. 6. Carybdea sp.: X-ray powder diffractogram of the crystals within the rhopalia. The computed positions for calcium sulfate hemihydrate are indicated as vertical bars.
The appearance of this massive statolith is decidedly different from the collection of single crystals in the rhopalia of the scyphozoans. We examined very young Carybdea sp. medusae and found many hexagonal crystals consisting of bassanite within one statocyst with a structure which is quite similar to the crystals of the coronate medusa Periphylla periphylla and other scyphozoan medusae (Tiemann et al. 2002; Becker et al. 2005). From the almost perfect shape of the crystals it can be concluded that they contain only one mineral in the form of a single crystal. X-ray diffraction showed unequivocally that the material is the water-deficient modification of calcium sulfate and certainly not gypsum (i.e. the dihydrate of calcium sulfate). The small amounts of sodium, potassium and phosphate that were detected can be related to cellular material, while the carbon peak is also caused by the sputtering process. In the young medusae examined here, a cluster of crystals develops at first, similar to P. periphylla. The crystals grow together during further development and form a radiating star before they merge into a solid mass. The concentric layers described by Ueno et al. (1995) in older cubozoan medusae statoliths must appear by the further uptake of calcium sulfate hemihydrate during growth. The structure of the statoliths of the young medusae is therefore highly similar to these structures in Scyphozoa as to size, mineralogy and prismatic appearance. We found a similar radial arrangement of the crystals (not fused) in the statolith of A. aurita by synchrotron radiation-based microcomputer tomography (SRmCT) (Becker et al. 2005). The anatomy of the rhopalia in Scyphozoa and Cubozoa was described by Russel (1970) and Werner (1984). The location of the eyes on the rhopalium and the distal located statocyst is
homologous in both groups. The anatomy of early statocyst-stages is comparable in coronata (Tiemann et al. 2002), Semeaostomeae, Rhizostomeae (Becker et al. 2005) and Cubozoa concerning their content of isolated prismatic crystals. The statocyst of scyphozoans stays on this stage during their whole life. The only development is the growth in size and number of the crystals. Contrarily the cubozoan statolith further develops into a solid ellipsoid. We interpret the appearance of isolated prismatic crystals at the beginning of the statolith development as a plesiomorphic feature of the class of Cubozoa. The subsequent development of a spherical statolith composed of thin layers is an autapomorphy. Schuchert (1993) considers the Scyphozoa and the Cubozoa as sister groups because of the existence of rhopalia, which derive from polyp tentacles. Marques and Collins (2004) created the new taxon Staurozoa, postulated as sister group of the Cubozoa and both groups together as sister group of the other scyphozoans. The appearance of the biomineral calcium sulfate hemihydrate, or bassanite, in statocyst of Cubozoa and Scyphozoa confirms their close relationship. The formation and use of the unusual (and within the animal kingdom unique) hygroscopical biomineral bassanite is an ancient attribute of both groups, which had to have a pelagic generation already at that time. It is possibly preserved because of its high density compared to dihydrate (gypsum).
Acknowledgements We are grateful to HASYLAB at DESY, Hamburg, for generous allocation of beamtime and to Drs. C. Baehtz and M. Knapp for experimental assistance. We thank Dr. D. Keyser and R. Walter (Hamburg) for assistance with electron microscopy.
References Abriel, W., Nesper, R., 1993. Bestimmung der Kristallstruktur von CaSO4(H2O)0.5 mit Ro¨ntgenbeugungsmethoden und mit Potentialprofil-Rechnungen. Z. Kristallogr. 205, 99–113. Ax, P., 1995. Das System der Metazoa I. Ein Lehrbuch der phylogenetischen Systematik. Fischer, Stuttgart. Becker, A., So¨tje, I., Paulmann, C., Beckmann, F., Donath, T., Boese, R., Prymak, O., Tiemann, H., Epple, M., 2005. Calcium sulfate hemihydrate is the inorganic mineral in statoliths of Scyphozoan medusae (Cnidaria). Dalton Trans. 1, 1545–1550. Chapman, D.M., 1985. X-ray microanalysis of selected coelenterate statoliths. J. Mar. Biol. Assess. UK 65, 617–627.
ARTICLE IN PRESS H. Tiemann et al. / Zoologischer Anzeiger 245 (2006) 13–17
Marques, A.C., Collins, A.G., 2004. Cladistic analysis of Medusozoa and Cnidarian evolution. Invertebr. Biol. 123 (1), 23–42. Pollmanns, D., Hu¨ndgen, M., 1981. Licht- und elektronenmikroskopische Untersuchung der Rhopalien von Aurelia aurita (Scyphozoa, Semaeostomae). Zool. Jb. Anat. 105, 508–525. Russel, F.S., 1970. The medusae of the British Isles. II. Pelagic Scyphozoa with a supplement to the first volume on Hydromedusae. Cambridge University Press, Cambridge, pp. 1–284. Salvini-Plawen, L., 1978. On the origin and evolution of the lower metazoa. Z. Zool. Syst. Evol. Forsch. 16, 40–88. Schuchert, P., 1993. Phylogenetic analysis of the Cnidaria. Z. Zool. Syst. Evol. Forsch. 31, 161–173. Singla, C.L., 1975. Statocysts of Hydromedusae. Cell Tissue Res. 158, 391–407.
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Spangenberg, D., Beck, C.W., 1968. Calcium sulfate dihydrate statoliths in Aurelia. Trans. Am. Microsc. Soc. 87 (3), 329–335. Tiemann, H., So¨tje, I., Jarms, G., Paulmann, C., Epple, M., Hasse, B., 2002. Calcium sulfate hemihydrate in statoliths of deep-sea medusae. Dalton Trans., 1266–1268. Ueno, S., Imai, C., Mitsutani, A., 1995. Fine growth rings found in statolith of a cubomedusa Carybdea rastoni. J. Plankton Res. 17 (6), 1381–1384. Ueno, S., Imai, C., Mitsutani, A., 1997. Statolith formation and increment in Carybdea rastoni Haacke, 1886 (Scyphozoa: Cubomedusae): evidence of synchronization with semilunar rhythms. Proceedings of the Sixth International Conference on Coelenterate Biology. Werner, B., 1984. Cnidaria. In: Gruner, H.-E. (Ed.), Lehrbuch der speziellen Zoologie, Vol. 1. Fischer, Jena, pp. 11–305.