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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 7707

Wilhelm Foissner; [Morphologie und Morphogenese von Psilotricha succisa (O.F. Muller, 1786) NOV. COMB. (Ciliophora, Hypotrichida)]. Protistologica XIX(4):479-493, 1983

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The morphology and the morphogenesis of the hypotrichous ciliate Psilotricha succisa (O.F. Muller, 1786) nov. comb. are described. Urospina bicaudata Gelei, 1944 and Psilotricha acuminata Dingfelder, 1962 (partim) fall as synonyms of this species. The genera Psilotricha Stein, 1859 and Urospina Gelei, 1944 should be synonymized because their diagnoses are almost identical. The cirri of P. succisa appear to be very similar and are arranged in 7 slightly curved rows. Only close below the oral apparatus there is a short transverse row which is denoted "postoral oblique row". Moreover, during the morphogenesis frontal, ventral and marginal cirri are distinguishable. There are no caudal, buccal and true transverse cirri. The morphogenesis of P. succisa is similar to that described in the genera Uroleptoides, Pseudouroleptus, Kahliella, Cladotricha, and Kerona. Concerning the infraciliature these genera are likewise related to Psilotricha. The oral primordium evolves de novo between the postoral oblique row and the left marginal row. It invaginates at the beginning of the stomatogenesis, but later it migrates to the surface again. Four special features which had never been described in other hypotrichs characterize the development of the cirral rows. 1) The undulating membranes of the proter remain unchanged. Thus, they do not produce cirri. 2) The anlagen of the new cirri develop much later in the proter than in the opisthe. 3) Some cirri of the proter and the opisthe originate in very different ways. The development of the 3. cirral row of the opisthe from the parental postoral oblique row is especially remarkable. On the contrary, in the proter this row originates in the 3. parental cirral row. 4) The postoral oblique row develops from the 4 cirral row by terminal segregation. These peculiarities favour the preservation of the family Psilotrichidae Butschli, 1889. The genus Psilotricha is supposed to represent a primitive type of hypotrichous ciliates. The following characters are assumed to be plesiomorphic: 1) the uniformity of the cirri in the non dividing animal, 2) the lack of buccal, transverse and caudal cirri, 3) the less pronounced migrations of the cirri during the morphogenesis, 4) the lack of any sign of reorganization of the undulating membranes during stomatogenesis. The postoral oblique row could be a precursor of true transverse cirri, and the cirral rows 4 and 5 are similar to marginal cirral rows.