Selenocystis foliata (Ray) from Scolelepis fuliginosa Clpde. and its identity with Haplozoon sp.

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Abstract
1. The so-called parasitic dinoflagellate occurring in the gut of the polychaete worm Scolelepis fuliginosa Clpde. is described and is shown to be the sexual phase of the gregarine “Selenidium foliatum” Ray.2. The gametocytes (often very unequal) associate by their posterior ends while in situ. One remains attached and its epimerite is transformed into a foot-like organ serving to attach the gametocyst to the host throughout the rest of development. The gametocyst is elongate and pyriform (26−226 × 9−34 μ) and its formation involves very little alteration in the shape of the gametocytes. Solitary encystment also occurs.3. The first gametocytic nuclear division is described. Forerunners of the gamete nuclei are formed within the nuclear area of the gametocyte. Flagellated isogametes are formed. There is no residuum.4. The spores are spherical, averaging 8·5μ in diameter, the number depending on the size of the cyst enveloping them. When ripe, they contain four or eight spindle-shaped sporozoites 9·4−14 × 2−3·75μ and, in vivo, a central, spherical, refrigent residuum.5. A new genus Selenocystis is proposed for this organism, with S. foliata (Ray) as the type species. Although I have not found its asexual phase, the probability is that it may still be classified among the schizogregarines.