JOURNAL OF INVERTEBRATE PATHOLOGY 47, 184- 193 (1986) A New and Unusual Species of Coccidium (Apicomplexa: Agamococcidiorida) from Caribbean Scleractinian Corals STEVE J. UPTON~ Department of Biological Sciences, University of Texas at El Paso, El Paso, Texas 79968 AND ESTHER C. PETERS Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560 Received July 8, 1985; accepted October 15, 1985 Gemmocystis cylindrus gen. et sp. n. (Apicomplexa, Agamococcidiorida, Gemmocystidae fam. IL) is described from the mesenterial filaments of the Caribbean scleractinian corals Agaricia agaricites, Dendrogyra cylindrus, Diploria strigosa, Meandrina meandrites, Montastraea caver- nosa, Porites astreoides, P. porites, and Porites sp. (Cnidaria, Scleractinia). In histological sec- tions from D. cylindrus (type host), oocysts measured 13.3 x 7.6 (12-15 x 7-9) pm and had a thick oocyst wall. Shape index (length/width) 1.8 (1.5-1.9). A micropyle was present; but sporo- cysts, an oocyst residuum, and a polar granule were lacking. Initially, a thin, flexible oocyst wall was produced around the zygote following fusion of two sporozoites. Unequal, longitudinal fission of the zygote and of the resulting sporozoites, led to the formation of up to six sporozoites within the oocyst. Mature sporozoites measured 11.3 x 3 (10-12.5 x 2.5-3.5) km and had a granular cytoplasm and a single, large, basophilic nucleus; refractile bodies were absent. Mature oocysts were observed both excysting in situ and being discharged into the gastrovascular cavity. Other than vacuolation of gastrodermal cells of the mesenterial filament lobes during heavy infections, no pathology was evident in colonies of D. cylindrus, P. astreoides, or P. porites. However, the presence of coccidian oocysts in A. agaricites, M. meandrites, and M. cavernosa was associated with loss of zooxanthellae, resulting in patchy bleaching and necrosis of tissues over the surface of these colonies. 0 1986 Academic Press. Inc. KEY WORDS: Apicomplexa, Gemmocystidae fam. n., Gemmocystis cylindrus gen. et sp. n., coc- cidia, coral, Cnidaria. Anthozoa, Scleractinia, Caribbean. INTRODUCTION The phylum Apicomplexa comprises about 4000 species of totally parasitic pro- tozoa that infect a wide range of verte- brates and invertebrates. However, few re- ports exist describing these taxa from non- coelomates. Canning (1962) described Legerella helminthorum, a coccidian para- sitic in the nematode, Mononchus compos- ticola, and briefly reviewed other reports of coccidia from nematodes. Peters (1984a) tentatively identified a gregarine from the scleractinian coral, Porites porites, as Ne- matopsis sp. She also reported spores of a r To whom correspondence should be addressed. previously undescribed coccidian infecting mesenterial filaments of four species of scleractinian corals: Diploria strigosa, Meandrina meandrites, Montastrea caver- nosa, and Porites astreoides. Spores were 12 x 6-7 pm, contained three or more nu- clei, and were Feulgen-positive in histo- logical sections. However, further develop- mental stages were not observed and, thus, she was unable to provide clues to the tax- onomic affinities of the organism. This paper presents further observations of this coccidium from histologic sections of eight Caribbean scleractinian coral species, and provides data on the taxonomic relation- ships between this coccidum and other members of the Apicomplexa. 0022-201 l/86 $1.50 Copyright 0 1986 by Academic Press, Inc. All rights of reproduction in any form reserved. 184