Abstract
The largest known Aspidisca species, A. magna Kahl, 1932, was found from coastal waters near Qingdao (Tsingtao), northern China, and investigated using both the "wet" silver nitrate and protargol staining method. Based on the living observation and impregnated individuals, improved diagnosis and morphometric data are provided. As an additional contribution, the morphogenesis in Aspidisca magna during binary fission was revealed and summarized as follows: 1) the parental adoral zone of membranelles and paroral membrane are retained by the proter; 2) the oral primordium of the opisthe develops hypoapokinetally behind the posterior part of the adoral zone of membranelles; 3) five frontoventral-transverse cirral anlagen are formed de novo, initially as primary primordia, and develop into 3: 3: 2: 2: 1 cirri from left to right, respectively in both dividers; 4) the leftmost frontoventral cirrus is generated from an independently formed cirral anlage in both dividers. In the present work, Chinese and Korean populations of A. leptaspis Fresenius, 1865 were investigated respectively to support the importance of living characteristics in identification of Aspidisca species. The isolation of A. magna and A. leptaspis from other congeners are also firmly demonstrated by the SSU rRNA gene sequence alignments.