Taxonomy, ontogeny and molecular phylogeny of anteholosticha marimonilata spec. nov. (Ciliophora, hypotrichida) from the yellow sea, China

The morphology, morphogenesis and molecular phylogeny of the marine ciliated protozoan Anteholosticha marimonilata spec. nov., isolated from mollusc-farming waters of the Yellow Sea, Qingdao, PR China, were investigated using microscopic observations of live and protargol-impregnated specimens and by small subunit rRNA gene sequence analysis. The novel species could be distinguished by the following features: an elongated elliptical body, in vivo size 80-160 um x 30-50 u.m; an adoral zone consisting of about 36 membranelles; three frontal, one parabuccal, one buccal, two frontoterminal and usually two pretransverse ventral cirri; 10-13 transverse cirri; a midventral complex composed of 12-17 pairs of cirri only, terminating in posterior 1/5; four or five dorsal kineties; two types of colourless cortical granules; four to nine moniliform macronuclear nodules and one to three micronuclei, and a contractile vacuole positioned at mid-body. Hitherto, the ontogenesis of the genus Anteholosticha has been regarded as rather diverse, which was confirmed by the morphogenetic processes of this novel species. The most noteworthy feature of A. marimonilata was that the proter retained almost the entire parental adoral zone except for a few proximal membranelles that were renewed in situ. The SSU rRNA gene sequence information clearly discriminated this isolate from its congeners. Molecular phylogenetic analyses demonstrated, with high statistical support, that A. marimonilata branched as a sister lineage to the Nothoholosticha-Pseudokeronopsis clade and hence belongs to the core part of the order Urostylida.