Morphology and Morphogenesis of Metopus hasei Sondheim, 1929 and M-inversus (Jankowski, 1964) nov Comb. (Ciliophora, Metopida)

The morphology and morphogenesis of Metopus hasei Sondheim, 1929 and M. inv ersus (Jankowski, 1964) n. comb. were investigated using live observation, silver impregnation, and scanning electron microscopy. Metopus has a spiral body organization and the ventral margin of the preoral dome bears five sp ecialized ciliary rows, that form the so-called perizonal stripe. Division is homothetogenic, occurs in freely motile (i. e. non-encysted) condition, and includes a partial reorganization of the parental oral apparatus. Durin g division, the complicated cell shape becomes ellipsoidal and all ciliary rows arrange meridionally, Stomatogenesis is entirely somatic (congruent to pleurotelokinetal) and commences with the formation of kinetofragments in some dorsolateral kinetics. The fragments become the opisthe's adoral membr anelles, while the paroral membrane is generated by the left two perizonal ciliary rous, which proliferate kinetids intrakinetally. The perizonal stri pe of the opisthe is generated by the three right parental perizonal kineti cs, which divide, and by two dorsolateral ciliary rows, which are added. Th e morphogenetic processes. especially the unique mode of formation of the p aroral membrane, are used to define the order Metopida Jankowski, 1980 n. s tat. more properly. The ontogenetic, ultrastructural, and sequence data ava ilable give no clear indication about metopid phylogeny, but definitely exc lude metopids from the classical hetetotrishs, with which they were classif ied for more than 100 years. Accordingly. we place the Metopida as incertae sedis in the subphylum Intramacronucleata Lynn. 1996.