Observations on the Sporozoa Inhabiting the Gut of the Polychaete Worm Polydora flava Claparède

1. A detailed description is given of a coccidian which parasitises the nuclei of the intestinal cells of the polychaete worm Polydora flava Claparède. The final stages in sporogony have not been observed; nevertheless, this is the first record, from an annelid worm, of an eimeriid which shows a striking resemblance to those Coccidia occurring in the higher animals. It is also the first record of an intranuclear parasite from an annelid.2. From the gut of the same worm, a new species of Selenidium is described. It differs from all other species, hitherto recorded, in the possession of an axial tube, which completely encloses the nucleus and extends from one end of the organism to the other: hence it is proposed to name this organism Selenidium axiferens. The anterior end of the trophozoite shows a circlet of siderophilous bodies, which Ray (1930 a) has shown to be characteristic of the genus.3. Both uninucleate and multinucleate intracellular forms, with polar groups of chromatic globules, have been discovered in great abundance on six occasions; no merozoites have been found, but evidence is submitted to show that these intracellular forms represent the schizogonic phase in the life-cycle of the Selenidium.4. Sporogony follows closely that described for other species, but the final stages have not been observed. The gametocysts measure 48 × 50–70 × 63μ.5. Association and cyst formation are described in Polyrhabdina polydorae Caul. & Mesn. (?) for the first time. Innumerable nuclei make their appearance in each gametocyte, before ejection of the cysts into the sea-water takes place. Gametocysts can easily be distinguished from those of Selenidium axiferens, not only by their morphology, but also by their greater size (98 × 90–105 × 100μ).