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Fine structure of Marteilioides chungmuensis n. g., n. sp., parasite of the oocytes of the oyster Crassostrea gigas
Fine structure of M~rtei~iaides chu~g~ue~sis the oyster Crassostrea gigas
n. g., zl. sp., parasite of the oocytes of
M. COMPS”, MS. PARK’ and I. DESPORTES3 ‘IFREMER, 1 rue Jean Vilar, 342 S&e (France) ‘Fisheries Research and Development Agency, Busan (Korea) 3Laboratoire de Cytophysiologie des Protozoaires, 105, boulevard Raspail, 75006 Paris (France) (Accepted 20 March 1987) An ovarian parasite of the oyster Crassostrea gigas has been observed on several occasions in the Pacific sector of production of this species (Matsuzato et al., 1977; Chun, 1979). Uttrastructurai studies carried out on infected oysters found in Korea in 1984, have allowed detailed examination of the structure and consequently the systematic position of this parasite, until now considered as an amoeba-like protistan. The earliest known stages consist of a stem cell or primary cell, including a secondary cell in which ovoid haplosporosomes are found f Fig. 1) . During sporulation, 2 or 3 secondary cells are produced by exogenous budding and, within each secondary ceII evolving into a sporont, one tertiary cell differentiates (endogenous budding); then, haplosporosomes form in the young sporont (Fig. 2). Internal cleavages involve the differentiation of one tricellular spore per sporont. The outermost spore cell contains membrane-bounded osmiophilic bodies: the middle and the innermost spore cells show high density of cytoplasmic ribosomes (Fig. 3 ) . The mechanism of spore formation from a stem cell is characteristic of the Paramyxea Levine 1980, in which the ovarian parasite has been included, but its differences from the other Paramyxea currently know have lead to its classification in a new genus and species, Marteilioides chungmuensis gen. n., sp. n., described by Comps et al. (1986).
Fig. 1. Earliest observable stage of the parasite. Primary cell (cl), secondary cell (~2). Ultrathin section. X 11000. Fig. 2. Advanced developmen~l stage. Nucleus of the stem cell (n 1) , secondary cell (c2 ) , tertiary cell (~3). Ultrathin section. x 8 000.
265
Fig. 3. Tricellular spore differentiated within the sporont. Spores cells (xl, section. X 9 000.
~2, ~3). Ultrathin
REFERENCES Chun, SK., 1979. Amoeba infectionin oyster (Cr~sos~reug~~). Bull. Korean Fish. Sot., 12 (4) : 281-285. Comps, M., Park, MS. and Desportes, I., 1986. Etude ~trastN~ur~e de Mur~eilioi~es chungmuensis n. g., n. sp., parasite des ovocytes de l’hustre Cmssostrea gigas Th. Protistologica, 22 (3): 279-285. Matsuzato, T., Hoshina, T., Arakawa, K, and Masumura, K., 1977. Studies on the so-called abnormal egg-mass of Japanese oyster, Crassostrea gigas (Thunberg) . I. Bull. Hiroshima Fish. Exp. Stn., 8: 9-25.
n. g., zl. sp., parasite of the oocytes of
M. COMPS”, MS. PARK’ and I. DESPORTES3 ‘IFREMER, 1 rue Jean Vilar, 342 S&e (France) ‘Fisheries Research and Development Agency, Busan (Korea) 3Laboratoire de Cytophysiologie des Protozoaires, 105, boulevard Raspail, 75006 Paris (France) (Accepted 20 March 1987) An ovarian parasite of the oyster Crassostrea gigas has been observed on several occasions in the Pacific sector of production of this species (Matsuzato et al., 1977; Chun, 1979). Uttrastructurai studies carried out on infected oysters found in Korea in 1984, have allowed detailed examination of the structure and consequently the systematic position of this parasite, until now considered as an amoeba-like protistan. The earliest known stages consist of a stem cell or primary cell, including a secondary cell in which ovoid haplosporosomes are found f Fig. 1) . During sporulation, 2 or 3 secondary cells are produced by exogenous budding and, within each secondary ceII evolving into a sporont, one tertiary cell differentiates (endogenous budding); then, haplosporosomes form in the young sporont (Fig. 2). Internal cleavages involve the differentiation of one tricellular spore per sporont. The outermost spore cell contains membrane-bounded osmiophilic bodies: the middle and the innermost spore cells show high density of cytoplasmic ribosomes (Fig. 3 ) . The mechanism of spore formation from a stem cell is characteristic of the Paramyxea Levine 1980, in which the ovarian parasite has been included, but its differences from the other Paramyxea currently know have lead to its classification in a new genus and species, Marteilioides chungmuensis gen. n., sp. n., described by Comps et al. (1986).
Fig. 1. Earliest observable stage of the parasite. Primary cell (cl), secondary cell (~2). Ultrathin section. X 11000. Fig. 2. Advanced developmen~l stage. Nucleus of the stem cell (n 1) , secondary cell (c2 ) , tertiary cell (~3). Ultrathin section. x 8 000.
265
Fig. 3. Tricellular spore differentiated within the sporont. Spores cells (xl, section. X 9 000.
~2, ~3). Ultrathin
REFERENCES Chun, SK., 1979. Amoeba infectionin oyster (Cr~sos~reug~~). Bull. Korean Fish. Sot., 12 (4) : 281-285. Comps, M., Park, MS. and Desportes, I., 1986. Etude ~trastN~ur~e de Mur~eilioi~es chungmuensis n. g., n. sp., parasite des ovocytes de l’hustre Cmssostrea gigas Th. Protistologica, 22 (3): 279-285. Matsuzato, T., Hoshina, T., Arakawa, K, and Masumura, K., 1977. Studies on the so-called abnormal egg-mass of Japanese oyster, Crassostrea gigas (Thunberg) . I. Bull. Hiroshima Fish. Exp. Stn., 8: 9-25.