Philodina koreana new species

Figures 1 and 2

Holotype and paratypes. In permanent slides, deposited in the collection of the National Institute of Biological Resources, Incheon, Korea (holotype: KOSPIV0000237111; two paratypes: KOSPIV000 0 237112, and KOSPIV0000237113). Specimens isolated from mosses, lichens and soil at Jang-neung, Yeongwol-gun, Gangwondo, collected by Min Ok Song and Chang-Ho Lee on Aug. 1, 2015.

Type locality. Jang-neung, Yeongwol-gun, Gangwon-do, Korea. GPS coordinates based on the WGS84 datum 37°11'51.6"N / 128°27'09.9"E.

Material. Seven specimens sorted out from mosses, lichens and soil at Jang-neung, Yeongwol-gun, Gangwondo.

Differential diagnosis. The most prominent characteristic of this new species is the extremely small spurs with very wide interspace between them. The spurs of P. parvicalcar De Koning and P. proterva Milne seem to be morphologically similar to those of P. koreana n. sp. However, the spurs of these three species show clear differences in detailed morphology. In P. parvicalcar, spurs are conical, highly divergent and with narrow and slightly convex interspace. In a case where the divergent conical spurs have narrow tips, two inner margins of wide-spread spurs together with outer margin of interspace can be seen as a wide interspace with a small spur at each side (De Koning, 1947, pl. VIII, fig. 38c). Likewise, the spurs of P. proterva are usually big, conical, pointed and with narrow interspace. In Donner (1965), variable forms of spurs of P. proterva are presented in Fig. 168d, where the similar case as P. parvicalcar is shown. In these cases, outer margin of interspace, which is a combination of two inner margins of divergent conical spurs and the outer margin of original interspace, overhang the dorsal margin of pseudosegment bearing the spurs, while that of P. koreana n. sp. coincide with the dorsal margin of the spur pseudosegment (Figs 1 c and 2b). Therefore, P. koreana is the only Philodina species known so far that has extremely small spurs and a very wide interspace.

In addition, this new species is easily distinguished from P. proterva and P. parvicalcar by the morphologies of disc retractor and upper lip, respectively. The disc retractor of P. koreana is slightly convex and trilobed medially while that of P. proterva is V-shaped or bilobed medially. The upper lip of P. koreana n. sp. is arched while that of P. parvicalcar is bilobed.

Description. Integument smooth. Rostral lamella bilobed and each lobe round; slightly wider than width of anterior end of rostrum. Rostrum round and short; ratio of rostrum width to head width about 1:1.7. Corona slightly wider than collar (cingulum) width; ratio of corona width to collar width about 1.2:1. Upper lip arched, higher than sulcus, lower than base of disc retractor and much lower than trochal discs. Pedicel rather short. Sulcus much narrower than pedicel width; slightly wider than a half of pedicel width. Disc retractor U-shaped with convex sides; slightly trilobed and convex medially. Pharyngeal tube much shorter than trophi length. Dental formula 1+2/2+1. Trunk cylindrical in creeping; greatest trunk width almost as wide as greatest neck width in creeping; greatest trunk width in feeding slightly wider than corona. Rump gradually tapering to foot. Foot short and its length about 1/4 of trunk length in creeping; cylindrical in creeping and with 5 pseudosegments. Spurs fingertip-shaped, very small, short and thin; interspace very wide and about 6-7 times as wide as spur base width.

Measurements. Rostrum width 13–14 µm. Corona width 39–43 µm. Collar width 33–36 µm. Total length in creeping 229–238 µm. Greatest trunk width in creeping 30–36 µm. Greatest foot width in creeping 14–16 µm. Largest rump width in creeping 22–23 µm. Head length in creeping 32–38 µm. Neck length in creeping 46–50 µm. Rump length in creeping 31–34 µm. Spur length 1.7–2 µm.

Distribution: The new species is known only from its type locality.

Etymology: The specific name koreana is derived from the country, the Republic of Korea, where the type locality is located.