Heliospora n.g. and Rotundi^ta n.g., Gregarines of Gammarus pulex

THE gregarines of Gammarus pulex L. have long been known, in fact they were some of the earliest of these Sporozoa to be observed (Text-figs. 1-3). However,.so far, no adequate description has been given of the gametes and spores which are the most important stages from the systematic point of view. Lady Muriel Percy, who worked in this Department from 1925 to 1929, helped in the investigation of spores by collecting infected Gammarus from different localities and isolating the Gregarine cysts for observations. From her notes and figures together with mine, which extend at intervals over the last quarter of a century, I have endeavoured to elucidate the life-histories of these two gregarines for which, I regret to say, it has been necessary to establish new genera as above. Apparently Siebold was the first to study the trophozoites—some time in the early eighteen-forties. He did not describe them in his paper of 1839, ^ has been erroneously stated by several writers, but gave Kolliker permission to incorporate his description in a postscript to his (Kolliker's) paper of 1848. There, one can find quite recognizable figures (29 a and j8) of a thread-like form, G. longissima and (y) of a shorter, more rotund form. Siebold and others (Labbe, 1899) were uncertain whether the latter was a young stage of the former. They were separated in the same year, 1848, by Frantzius, who attached the long thread-like gregarine of Gammarus pulex to the genus Didymophyes (just created by Stein for D. gigantea of Oryctes and D. paradoxa of Geotrupes), leaving the short form occurring with it as G. gammari?. He was followed by Diesing, 1859, who definitely stated that he excluded the latter from G. longissima and consequently this species G. gammari is now ascribed to Diesing owing to the uncertainty of Frantzius and the original observer Siebold. There is no doubt that 'longissima' and 'gammari' are their correct specific names. To find correct generic names has been more difficult. The threadlike form, even without knowledge of its cyst, could not be kept in the genus Gregarina, and Poisson (192ib), realizing that it also had no place in the genus Didymophyes, changed it to one Uradiaphora suggested by Mercier (19126 and c; see also p. 32 below) for a gregarine found in the freshrwater shrimp [Quarterly Journal Microscopical Science, Vol. 90, part 1, March 1949]