Partial retention of parental ciliature during morphogenesis of the ciliate Coniculostomum monilata (Dragesco & Njiné, 1971) Njiné, 1978 (Oxytrichidae, Hypotrichida).

Morphogenesis of Coniculostomum monilata as revealed by protargol staining shows formation of 18 Frontal-Ventral-Transverse (FVT) cirri from 6 cirral streaks. Only 3 parental FVT cirri participate in the formation of cirral streaks. While only one row of right marginal cirri (RMC) is formed during division, the non-dividing cell possesses 3-5 RMC rows. This corticotype is explained by the fact that during division parental RMC rows are retained and inwardly displaced, the innermost row being resorbed. As the cell elongates, cirri in the retained rows space out; each row is equatorially cleaved during cytokinesis. A similar retention of dorsomarginal rows occurs on the dorsal surface. Based on synapomorphies shared by C. monilata and Stylonychia mytilus, we propose that C. monilata is an evolved oxytrichid. The regular retention of ciliary structures through several generations is, however, a unique character amongst the evolved oxytrichids and may be considered as an autapomorphy to describe C. monilata. Another such feature of C. monilata is the moniliform macronucleus, unique among the advanced oxytrichids. The present study reaffirms the importance of morphogenetic criteria in ciliate systematics. The original description of C. monilata Njiné, 1978 has been rectified with respect to the nomenclature of cirri and phylogenetic status of the species.