Abstract
A little-known marine hypotrich, Apokeronopsis ovalis (Kahl, 1932) nov. comb. [basionym: Holosticha (Keronopsis) ovalis Kahl, 1932], found in coastal waters near Qingdao, China, was investigated with emphasis on its living morphology, infraciliature and morphogenesis. Based on the data obtained, an improved diagnosis and redescriptions are supplied. It differs from all the congeners mainly by the body shape, colour and the distribution of two kinds of cortical granules and the morphometric as well as the molecular data. Apokeronopsis ovalis is distinct genetically (4.34%, 3.9% and 4.41% in the SSU rRNA gene sequence) from its congeners, A. crassa, A. bergeri and A. wrighti, respectively. Ontogenesis is basically similar to the pattern as revealed in congeners, which is characterized by the de novo formed oral primordium in the proter as well as the apokinetal formation of both the dorsal kinety and marginal row anlagen in both dividers. In addition, a key is provided for all known morphospecies in this genus.