Philodina tranquilla Wulfert, 1942

Lee, Sue Yeon, Yoo, Jung Sun & Kim, Seung Tae, 2017, New records of 13 rotifers including Bryceella perpusilla Wilts et al., 2010 and Philodina lepta Wulfert, 1951 from Korea, Journal of Species Research 6, pp. 26-37 : 33

12. Philodina tranquilla Wulfert, 1942

Philodina tranquilla Wulfert, 1942, pp. 195-196 , Abb. 5a-d; Donner, 1965, p. 211, fig. 155e.

Material examined. Two specimens found in wet mosses at a stream around Daegwallyeong, Pyeongchang-gun, Gangwon-do, 37°41 ʹ 19.7 ʺ N 128°45 ʹ 39.0 ʺ E, 5 June 2016.

Diagnosis. Two orange eyes. Corona slightly wider than cingulum pad. Upper lip arched and much lower than trochal discs; bilobed medially and with a wide depression between lobes. Sulcus as wide as pedicel width and convex medially. Teeth 2 + 1/1 + 2. Spurs plump proximally and abruptly tapering to blunt ends from the middle part.

Measurements. Total length in feeding 125 μm. Greatest trunk width in feeding 60 μm. Corona width 41 μm. Cingulum width 37 μm. Spur length 5 μm.

Remarks. This species is similar to Philodina acuticornis odiosa Milne, 1916 , but it can be distinguished from the latter by the following characteristics: (1) the corona of P. tranquilla is slightly wider than cingulum pad, while that of the latter is much wider than cingulum pad, and (2) the dorsal toes of P. acuticornis odiosa are always extended a little even during feeding, while those of P. tranquilla are not.

This species is rather rare and has been reported from Japan and New Zealand after its description from Germany. The first Asian record of this species was from Japan by Hayashi et al. (1998).

World distribution. Japan ( Hayashi et al., 1998), Germany ( Wulfert, 1942), New Zealand ( Haigh, 1963) and Korea.

Deposition. Deposited in the collection of the National Institute of Biological Resources, Incheon, Korea (ZIIY IV0000004845, ZIIYGR0000000009).