Morphogenesis and Systematic Position of Oxytricha gigantea HORVATH 1933 (Ciliophora, Hypotrichida), HELMUT BERGER, Hydrologische Untersuchungsstelle Salzburg, Lindhofstrasse 5, A-5020 Salzburg (Austria/Europe) and WILHELM FOISSNER, Universität Salzburg, Institut für Zoologie, Hellbrunnerstrasse 34, A-5020 Salzburg (Austria/Europe).
KAHL, (Tierwelt Dtl., 1935, 30, p 841) transferred O. gigantea to the genus Urosoma KOWALEWSKI 1882, because of its elongated and posteriorly converging body shape. To gain more information about the systematic position of this species, the morphogenesis was investigated and compared with that of a typical member of the genus Urosoma, U. macrostyla (FOISSNER, Arch. Prot istenkd., 1983, 127, 413). The main difference between the morphogenetir patterns of these species, that argues for the retention of O. gigantea in the genus Oxytricha, exists in the formation of the fronto-ventral-transverse (FVT) streaks. Six "primary primordia" are formed in U. macrostyla. They divide in the middle stages and form the 6 "secondary primordia" of the proter and the opisthe. Contrary, only the streaks IV (?), V, and VI of the proter arise from the streak IV of the opisthe in O. gigantea. This type of FVT streak formation is also know from other Oxytricha species. The classification in this genus is also supported by the position of the cirrus III/2. In Oxytricha this cirrus is always situated more posteriorly than the cirrus 4 of streak VI, whereas it is always situated more anteriorly than the cirrus VI/4 in Urosoma. Very probably, the position of the cirrus III/2 is the most apporiate character to separate Oxytricha and Urosoma, since Urosoma species are known to exist, which do not have the tail-like posterior end of the type-species, U. cienkowski. (Supported by the Fonds zur Foerderung der wissenschaftlichen Forschung, Projekt Nr. P 5889).
Keywords: alphataxonomy, Taxonomie, Oxytrichidae, Hypotrichia, Hypotricha, Hypotrichida, stichotrichia, Stichotrichine, Stichotrichid, ontogenesis, cell division, Zelteilung, , Ciliate, Ziliaten, Wimpertierchen, FVT, anlage, primordium, primär primordia,
Dr Helmut BERGER
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