Margolisiella kabatai gen. et sp. n. (Apicomplexa: Eimeriidae), a parasite of native littleneck clams, Protothaca staminea, from British Columbia, Canada, with a taxonomic revision of the coccidian parasites of bivalves (Mollusca: Bivalvia).

Two of 98 native littleneck clams, Protothaca staminea Conrad, from Cooper's Cove, Sooke Basin were infected with an eimeriorin coccidian parasite. Merogonic gamontogonic and sporogonic development were observed in renal tubular epithelial cells. Sporulation of the oocysts occurred within the host. Mature oocysts were spherical mean 41 microns (range 30-44), and contained about 32 subspherical sporocysts (9 x 10 microns), each of which contained 4 sporozoites. Spherical 19 microns (18-20), cyst-like structures and smaller multinucleate bodies, some of which resembled sporocysts, were also seen. A review of the coccidian parasites of bivalves led to the erection of the new genus, Margolisiella (family Eimeriidae Minchin, 1903) to accommodate M. kabatai sp. n., the parasite in Protothaca staminea described herein. Four previously described monoxenous species (Pseudoklossia patellae Debaisieux, P. chitonis Debaisieux, P. tellinovum Buchanan and P. haliotis Friedman, Gardner, Hedrick, Stephenson, Cawthorn et Upton) were also transferred to the new genus. The 2 remaining possibly heteroxenous species (P. pelseneeri Léger and P. glomerata Léger et Duboscq) were retained in the genus Pseudoklossia Léger et Duboscq (family Aggregatidae Labbé, 1899).