The morphology, morphogenesis and small subunit (SSU) rRNA gene-based phylogeny of Neourostylopsis flava paraflava nov. subsp. were investigated. Neourostylopsis flava paraflava nov. subsp. was separated from N. flava flava nov. stat. by habitat (brackish water vs. fresh water), pretransverse cirri (absent in all specimens vs. present in 15% of specimens), the numbers of frontal cirri (8-15 vs. 6-8) and left marginal cirral rows (6-9 vs. 4-5). The main morphogenetic features of N. flava paraflava nov. subsp. are as follows: (1) streaks I-VI (or I-VIII, deduced from morphological data) produce the bicorona; (2) the oral primordium and frontoventral-transverse cirral anlagen in the opisthe are formed de novo on the cell surface; (3) the numerous macronuclear nodules fuse into a branch-like mass; (4) two pretransverse ventral cirri are formed initially but disappear in the later stages; and (5) some of the frontoventral-transverse cirral anlagen develop in a primary mode. Based on SSU rDNA sequence data, phylogenetic analyses show a close relationship between N. flava paraflava nov. subsp., N. flava flava nov. stat. and other Neourostylopsis species. An improved diagnosis for Neourostylopsis is provided: Urostylidae with five or more frontal cirri which form an indistinct or distinct bicorona; pretransverse cirri present or absent; transverse cirri present; buccal cirri present; two frontoterminal cirri; midventral complex composed of midventral pairs only; more than one row of marginal cirri on each side which derive from individual anlagen within each parental row; caudal cirri lacking; three dorsal kineties; endoral and paroral rather long, endoral straight, paroral distinctly curved anteriorly.
Keywords: Brackish water; Ontogenesis; SSU rDNA sequence; Systematics; Taxonomy; Urostylida.
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