Melita shimizui (Uéno, 1940) (Figs. 6, 7)

(Korean Name: Dung-geun-son-me-li-ta-yeop-sae-u, new)

Crangonyx shimizui Uéno, 1940; 74, figs. 49–73.

Melita shimizui – Karaman, 1981: 44.– Yamato, 1988: 86.

Material examined. Adult male, 6.9 mm, cat no. NIBRIV0000919533, adult female, 3.4 mm, cat no. DKUAMP202405, Songcheon Stream, Geocha-ri, Seobu-myeon, Hongseong-gun, Choungcheongnam-do, Korea, 36°33′41″N, 126°28′58″E, 19 April 2019, collected by S.H. Im.

Additional material examined. See figure 1 and table 1 for station details.

Description. Adult male, NIBRIV0000919533.

Body (Fig. 6A, 7A) dorsally smooth. Head, lateral cephalic lobe subround; eye round, black, small. Urosomite 2 with 2 robust setae dorsolaterally.

Antenna 1 (Fig. 7B), peduncular article 1, with 1 robust seta near the posteroventral corner; peduncular article 2 elongate, with 2 setae on dorsal margin, with group of 2 setae on ventral margin; peduncular article 3 short, with 10 setae on ventral margin; length ratio of peduncular articles 1–3 = 1.00: 1.05: 0.51; flagellum 21-articulate, longer than peduncle, each article with medial and dorsal setae; accessory flagellum 2-articulate, article 1 elongate, length 0.80 x first flagellum article, article 2 minute.

Antenna 2 (Fig. 7C) short, but longer than peduncle of antenna 1; gland cone pointed; peduncular articles 4, 5 elongate, with group of setae on ventral margin; length ratio of peduncular articles 3–5 = 1.00: 2.33: 2.00; flagellum short, 9-articulate, article 1 elongate.

Gnathopod 1 (Fig. 7D), coxa trapezoidal, gradually widening, width 0.64 x length, with 4 setae on ventral margin; basis with 9 setae anteriorly and 4 setae posteriorly; merus posterior margin pubescent; carpus elongate, with pectinate setae on anterior corner, group of setae posteriorly; propodus subrectangular, with group of setae on anterior and posterior margins; palm short, gently convex, with small robust setae along the palmer margin; dactylus short, fitting palm; length ratio of articles 2–7 = 1.00: 0.29: 0.35: 0.64: 0.43: 0.21.

Gnathopod 2 (Fig. 7E), coxa subrectangular, width 0.63 x length, with 3 setae ventrally; basis elongate, with 1 long seta posteriorly; merus slightly produced posterodistally; carpus produced posteriorly, with 1 robust seta on anterodistal corner, posterior surface covered with pectinate setae; propodus large, subovate, anterior margin slightly convex, with 4 rows of setae medially, with group of setae on posterior margin, length 1.86 x width; palm oblique, serrate, with long and robust setae along the palmer margin; dactylus falcate, fitting palm; length ratio of articles 2–7 = 1.00: 0.33: 0.43: 0.70: 1.20: 0.70.

Uropod 1 (Fig. 7F), peduncle subrectangular, length 1.60 x outer ramus, with 7 lateral and 3 medial robust setae dorsally, with basofacial seta and 1 long distal robust seta laterally; outer ramus subequal to inner ramus in length, with 4 distal robust setae; inner ramus with 1 dorsal and 3 distal robust setae.

Uropod 2 (Fig. 7G), peduncle slightly longer than outer ramus, with 3 dorsolateral and 1 dorsomedial robust setae; outer ramus subequal to inner ramus in length, with 2 dorsal and 3 distal robust setae; inner ramus with 3 dorsal and 3 lateral robust setae.

Uropod 3 (Fig. 7H), peduncle short, length x 0.57 outer ramus, with 2 robust setae on ventral corner; outer ramus elongate, sublinear, uni-articulate, length x 5.63 width, with group of robust setae along dorsal and lateral margins; inner ramus scale-like, with 1 robust seta apically.

Telson (Fig. 7I) much longer than broad, length 1.23 x width, completely cleft, each lobe pointed apically, with 2 robust setae on inner margin, with 3 robust setae apically.

Female, 3.4 mm, cat no. DKUAMP202405.

Body (Fig. 6B) similar to that of adult male, but smaller than male, with oostegites.

Gnathopod 1 (Fig. 7J) similar to that of adult male, but less setose than that of adult male.

Gnathopod 2 (Fig. 7K) similar to that of adult male; propodus subrounded; palm less serrate than that of adult male.

Coxa 6 (Fig. 7L) ventral margin excavated medially; anterior lobe truncate distally, weakly hooked.

Salinity range. 0.6–34.0 psu

Molecular data. CO1 gene sequences (GenBank accession numbers PP600315, PP663868) were obtained from two Korean M. shimizui specimens. The sequences were aligned and compared with sequences from M. choshigawaensis (LC371923–371925) in Japan, M. aestuarina sp. nov. (PP620152, PP658244, PP664116) from Korea, and M. shimizui (LC371926–371928, LC637603, LC637604) from Japan (Table 2). Intraspecific variation of the CO1 gene sequence of M. shimizui ranged between 0.0 and 5.1% while interspecific variation ranged from a low of 11.6% (M. shimizui and M. aestuarina sp. nov.) to a high of 17.6% (M. shimizui and M. choshigawaensis) (Fig. 8, Table 3).

Remarks

Melita shimizui (Uéno, 1940) is similar to M. aestuarina sp. nov. and M. choshigawaensis, as mentioned above. However, M. shimizui is distinguished from its congeners based on the following features: 1) gnathopod 2, propodus subovate; 2) uropod 3, outer ramus linear, five times longer than wide; 3) coxa 6 weakly hooked in female (Labay, 2016; Tomikawa et al., 2018). Recently, Labay described a new subspecies, M. shimizui sakhalinensis from Sakhalin, characterized by a more elongated anterior lobe of female coxa 6 compare to M. shimizui (Labay, 2016). Our specimens are consistent with the description provided by Yamato (1988).

Distribution. Korea, China, Japan.