The morphology of the poorly-known freshwater urostylid ciliate Neokeronopsis spectabilis (Kahl, 1932) nov. gen. nov. comb., (Ciliophora: Urostylidae), with notes on its morphogenesis

Abstract

Neokeronopsis spectabilis (Kahl, 1932) nov. gen. nov. comb. (formerly Holosticha ( Keronopsis) spectabilis ), a large, freshwater urostylid ciliate, is redescribed following examination of protargol stained material. Its morphology is characterized by: flexible cortex; large size (368–500 μm long); large buccal field and long adoral zone of membranelles which curves across the apical cell margin to the right hand side of the body; two rows of frontal cirri each forming a bicorona; long midventral row of cirri arranged in pairs; one marginal cirral row on each side of the cell; a long row of well developed transverse cirri; 6–9 caudal cirri arranged in three rows, 2–3 cirri per row; 9–12 dorsal kineties; two ovoid macronuclear nodules. Morphogenetic events in N. spectabilis are characterized by the following: (1) the parental adoral zone of membranelles (AZM) is retained in the proter while in the opisthe the AZM is formed de novo from the oral primordium; (2) the undulating membrane anlage gives rise to the paroral and endoral membranes and to the anteriormost frontal cirrus; (3) the cirral anlagen form to right of the buccal field and give rise to the frontoterminal, midventral and transverse cirri; (4) the marginal row anlagen are formed within the old structures; (5) the dorsal anlagen form in two groups; Group 1 initially comprises 3 kineties which are formed within the 3 leftmost kineties of the parental structure, although the rightmost of these proliferates to form ca. 6–8 kineties; Group 2 comprises 5 kineties which form de novo near the anterior end of the right marginal row; (6) the caudal cirri are formed at the posterior end of the rightmost and the two leftmost kineties of the Group 1 dorsal anlagen; (7) the macronuclear nodules fuse to form a single mass which divides twice prior to the separation of the daughter cells. The new genus Neokeronopsis is established on the basis of this unique combination of morphological and morphogenetic characters. The generic diagnosis is as follows: urostylid with two arched rows of frontal cirri each forming a bicorona; long midventral row of paired cirri; one marginal row on each side of the body; frontoterminal, transverse and caudal cirri present; during morphogenesis, formation of dorsal kineties is of an Oxytricha -pattern. Neokeronopsis spectabilis is fixed as the type species of the genus.