Arch. Protistenkd. 132 (1986): 11-21 VEB Gustav Fischer Verlag Jena Departamento de Microbiologia, Facultad de Biologia, Universidad Complutense, Madrid, Spain Further Studies on Urocentrum turbo O. F. M. (Ciliata): Morphology and Morphogenesis By A. MARTIN-GONZALEZ, S. SERRANO, A. GUINEA and D. FERNANDEz-GALIANO With 19 Figures Key words: Urocentrum turbo; Ciliata; Stomatogenesis; Buccokinetal; Stomatogenic field Summary Stomatogenesis in Urocentrum turbo is buccokinetal, the oral structures in the opisthe (paroral kinety, stomatogenic field and three peniculi) are formed from the parental stomatogenic field. Also, the parental paroral kinety develops into the new stomatogenic field of the proter. During the bipartition process of this ciliate, the anterior infraciliar band of the parental cell splits into its two parts, an anterior one or fascia which originates the cingula and the posterior band of the proter, and a more posterior one or cingula which produces the anterior band of the opisthe. Biometrical and morphological characterisation were also made and our data are compared with the results obtained previously by other authors. Introduction The morphology of Urocentrum turbo, a species of the genus Urocentrum, has been previously studied by several workers using both optical microscopy with different silver impregnation methods (KLEIN 1927; KIDDER and DILLER 1934; FAURE-FRE- MIET 1954; ROQUE 1961; FERNANDEZ-GALIANO and GUINEA 1971) and electron microscopy (DIDIER and PUYTORAC 1968; DIDIER 1971). Despite of research carried out on stomatogenesis in this species by FAURE-FREMIET (1954), ROQUE (1961, 1973) and FERNANDEZ-GALIANO and GUINEA (1971), the results obtained have been contra- dictory. FAURE-FREMIET (1954) believes the "granular field" to be an oral structure giving rise to the entire oral apparatus in the opisthe whereas ROQUE (1961, 1973) refers to this field as a "vestibular" formation. According to the latter, the oral structures in the opisthe derive from the parental paroral kinety without the parti- cipation of the aforementioned field in stomatogenesis. Unfortunately, FERNANDEZ- GALIANO and GUINEA (1971) were not able to obtain images of the first stages of the oral division and so neither of these suppositions was proved although the absolute necessity for subsequent researchwork on this process was pointed out. Later PUYTO- RAC et al. (1984), in their aim to make a phenetic classification of the phylum Cilio- phora emphasized again the need for a detailed study on the stomatogenic process in Urocentrum since this group of features is a fundamental source of information for clarification of the systematic position of this species and its relations with other genera of ciliated protozoa.