Sipunculus

Abstract: SUMMARY Trie gregarines of Sipunculus, so often recorded during the last hundred years, prove to belong to two or more species of the genera Urospora and Lithocystis, and further information especially about the gametes and zygotes is much needed. The structure of the spores, the most diagnostic feature of gregarines, forces one to recognize three species, viz. Urospora Mgeri, U. hardyi, and Lithocystis lankesteri, as distinct from the original U. sipunculi Koll. "\ /TORE than a hundred years ago Kolliker (1848) described a parasite of JLVA the coelom of Sipunculus nudus from Naples which he called Gregarina sipunculi. He appears only to have examined a few specimens of S. nudus; one contained trophozoites described as generally roundish or pear-shaped, smooth, and active, later becoming associated and approximately spherical (see his Figs. 1-3); another specimen had many cysts near its posterior end, each containing numerous oval spores with thread-like tails rather more than half as long again as the spores themselves (his Fig. 4a). There is little doubt that this parasite should be put in Schneider's (1875) genus Urospora as U. sipunculi Koll., in spite of its being less elongated than most Urospora, and, as I pointed out (1915, p; 99), it requires much further study. Lankester working in Naples in the winter of 1871-2 on the anatomy of S. nudus had found numerous specimens infected with gregarines, and some of the spores drawn by him (Fig. 6 b, c), probably represent the above species. However, he described, p. 348, another spore found on various occasions, with a long 'shred-like filament dependent from one extremity, which is perfectly motionless'. This gregarine, which I was able to examine alive in Naples, 1929 (Text-fig. 3), should belong almost certainly to the genus Lithocystis (Giard 1876) and I propose to call it L. lankesteri for the present. Lankester said that the spores were preceded by spherical corpuscles; these were undoubtedly gametes or zygotes and presumably motionless, but apparently neither he nor any subsequent worker has been able to examine them alive, so that we do not know for certain that they are motionless, as are those of other Lithocystis (emended characteristics, Pixell Goodrich, 1915, 1925). From January to June 1921 A. C. Hardy was working in Naples, and some S. nudus he examined were infected with parasites. Among these were motile trophozoites of two distinct gregarines—one with a spiny cuticle (Text-fig. 1, A and B), the other smooth and squirming (Text-fig. 2); but, as no spores were