Abstract
The morphology and taxonomy of two marine Amphisiella species, isolated from mariculture waters in northern China, were investigated using standard techniques. One species corresponds well with the original description of the poorly known Amphisiella milnei (Kahl, 1932) Horváth, 1950 by remarkable characteristics, inter alia, (i) the additional cirri between the left frontal cirrus and the buccal cirrus, and (ii) ring-shaped structure in the anterior and posterior body portion (posterior one sometimes lacking). The detailed description of the cirral pattern and an informative ontogenetic stage first reveal that the additional cirri, which are uniformly absent in all congeners, originate from the frontal-ventral transverse cirral anlage I. The other species represents a new species of Amphisiella, A. sinica sp. nov. It is distinguished from its most closely related congener A. annulata (Kahl, 1928) Borror, 1972 by having numerous ring-shaped structures with a shallow brim more or less densely centralised at both ends of the body. Brief notes on the cell division and phylogenetic analyses based on small subunit (SSU) rRNA gene sequence for both organisms are also supplied in order to get further understanding of their systematic positions. The molecular information indicates that both organisms belong to two separate clades and confirms that the genus Amphisiella might be polyphyletic.