Krohnitta subtilis (Grassi, 1881)

Figs 3C, 4C, 8A, 9B, 11A-D

Spadella subtilis: Grassi, 1883: 16 p., table 1.

Krohnia subtilis: Fowler, 1906: 25-26 p., figs 86-88; Michael 1908: 269-270 p.

Krohnitta subtilis: Burfield & Harvey, 1926: 117 p., figs 45-50.; Thomson 1947: 22 p.; Tokioka 1965: 352-353 p.; Alvariño 1967: 18-20 p., fig. 9 A-D; Srinivasan 1979: 37-39 p., fig. 21 A-D; Michel 1984: 30 p., fig. 41; McLelland 1989: 158 p., fig. 5A-D; Park et al. 1990: 74-76 p., fig. 52.; Nair et al. 2008: 210 p., table 1.

Material examined.

Korea Strait (33°30.000'N, 125°54.000'E), 0-90 m depth, oblique towing with conical net, Feb 2020, NIBRIV0000895313 (one specimen); northern East China Sea (33°00.000'N, 127°4.098'E), 0-110 m depth, oblique towing with conical net, Feb 2020, NIBRIV0000895312 (one specimen) .

Description.

Total body length ranged between 10.8 and 11.5 mm and tail 27.3-33.7% of body length. Hooks 8-10. Anterior teeth 14. Slender and transparent body (Fig. 11A). Small head. One row of stout teeth arranged in fan shape (Fig. 9B). Collarette and intestinal diverticula absent (Fig. 11B). Grasping spine abruptly curved (Fig. 8A). Round eyes with eye pigments in “E” shape (Fig. 11B). Corona ciliata beginning in front of eyes with round shape (Fig. 11C). Lateral fins 29.4% of body length. Starting points of lateral fins 54.3% and ending points of lateral fins 82.2% of body length, respectively. One pair of lateral fins only rayed on outer edge, with forward ends equidistant from caudal septum (Fig. 11A, E). Caudal fin roughly round in shape (Fig. 11D). Seminal vesicles elongated with anterolateral-edge-opening touching both lateral fins and caudal fin (Fig. 11D).

Distribution.

This species is found in the epipelagic (0-200 m depth) and mesopelagic zones (200-500 m depth) of the Pacific, Indian and Atlantic Oceans (Pierrot-Bults and Nair 1991), the Indian water (George 1952) and the Tosa Bay in Japan (Ohnishi et al. 2014), while in this study, it was found in the epipelagic zone (0-110 m depth) of the Korea Strait and northern East China Sea (Fig. 1: stations KS05 and nECS04).

Ecology.

This cosmopolitan species can be found in tropical to temperate waters ( Alvariño 1967). The temperature ranged between 16.40 and 16.41 °C and salinity was 34.58 psu at the sampling stations of this study.

Remarks.

This species is clearly distinguished from K. pacifica by the presence of a rayless zone in the lateral fin. Furthermore, the presence of a pair of lateral fins with a wide rayless zone and a fan-shaped dentition in K. subtilis collected from Korean waters are consistent with the records of Alvariño (1967) and Bieri (1991). However, the location of the corona ciliata (in front of the eyes, Fig. 11C) of the species found in Korean waters was different from that of the previous records (located behind the eye). No specific pattern was observed through CBE staining on the body surface.