Amphipod (Crustacea: Malacostraca) fauna of the continental shelf region in the Southern Sea of Korea Author Kim, Kyung-Won Author Choi, Jae-Hong Author Shin, So-Yeon Author Kim, June Kim and Young-Hyo yhkim@dankook.ac.kr text Journal of Species Research 2024 13 2 159 177 journal article 10.12651/JSR.2024.13.2.159 2713-8615 13162179 6. Byblis longiflagelis Ren, 1998 űnjñḑü경ăNjẹ (ṳạ) * ( Figs. 5 , 6 , 11F ) Byblis longiflagelis Ren, 1998: 177 , Figs. 8 , 9 (cited from Ren, 2006 ); Ren, 2006: 167 , Fig. 56. Material examined. 1♂ , Site 4, 17 August 2022 ; 1♂ , Site 6, 17 August 2022 . Description. Male (MABIK CR00254534): Body ( Figs. 5A , 11F ) smooth, 11.1 mm long: Head ( Fig. 5A ) longer than pereonites 1 and 2 combined; rostrum short; corneal lens of eyes two paired, one pair located on upper distal end, the other located on apex of anterior cephalic lobe. Gnathopod 1 ( Fig. 5B ), coxa gradually expended anteroventrally, ventral margin serrated, with plumose setae; basis elongate, subrectangular, with 5 long setae and 1 robust seta on posterior margin; carpus elongate, about twice length of propodus, with unequal setae on posterior margin; propodus elongate-ovate, palm subchelate; dactylus falcate, with a nail. Gnathopod 2 ( Fig. 5C ) similar to gnathopod 1, but coxa subquadrate and smaller; carpus and propodus more elongated than those of gnathopod 1; length ratio of articles 2 - 7 = 1.00: 0.19: 0.31: 0.73: 0.30: 0.15. Fig. 5. Byblis longiflagelis Ren, 1998 , adult male. A, habitus; B, gnathopod 1; C, gnathopod 2; D, pereopod 3; E, pereopod 4; F, pereopod 5. Scale bars: A = 1.0 mm; B - F = 0.2 mm. Pereopod 3 ( Fig. 5D ), coxa similar to coxa 2; basis with simple setae on both margins; merus elongate, with plumose setae on distal half of posterior margin; carpus short, with 3 setae on anterodistal margin and 10 plumose setae on posterior margin; propodus slender, with several clusters of setae on anterior margin and 6 plumose setae on posterior margin; dactylus elongate and acute; length ratio of articles 2 - 7 = 1.00: 0.17: 0.65: 0.29: 0.28: 0.37. Pereopod 4 ( Fig. 5E ), coxa subquadrate, posterior margin with posteroproximal excavation, posterior tooth subacute and produced backward; basis and merus subrectangular, with a row of simple setae on anterior margin, simple and plumose setae on posterior margin; merus to propodus subrectangular, slender, with plumose setae along posterior margins; length ratio of articles 2 - 7 = 1.00: 0.20: 0.81: 0.29: 0.24: 0.27. Fig. 6. Byblis longiflagelis Ren, 1998 , adult male. A, pereopod 6; B, pereopod 7; C, uropod 1; D, uropod 2; E, uropod 3; F, telson. Scale bars: A - E = 0.2 mm; F = 0.1 mm. Pereopod 5 ( Fig. 5F ), coxa weakly bilobate; basis subovate, broadly expanded, with 12 plumose setae and 12 robust setae on anterior margin, posterior lobe somewhat produced; carpus subrectangular, with 9 robust setae on distal margin and 1 robust seta on anterodistal corner. Pereopod 6 ( Fig. 6A ) similar to pereopod 5, except coxa 6 with plumose setae anteroventrally and posterior lobe of basis weakly produced. Pereopod 7 ( Fig. 6B ), basis expanded posteroventrally, ventral margin slightly serrated, with densely plumose setae, posterodistal lobe extending far beyond distal end of merus; length ratio of articles 2 - 7 = 1.00: 0.15: 0.18: 0.28: 0.23: 0.09. Uropod 1 ( Fig. 6C ), peduncle subrectangular, subequal to outer ramus in length, with 5 dorsolateral and 5 ventrolateral robust setae; outer ramus longer than inner ramus. Uropod 2 ( Fig. 6D ) short; peduncle subrectangular, longer than rami; outer ramus longer than inner ramus. Uropod 3 ( Fig. 6E ), peduncle shorter than rami; both rami subequal in length, inner margin of inner ramus serrated. Telson ( Fig. 6F ) quadrangular, with distally rounded corners, cleft not reaching to the middle, each lobe with 2 short setules on outer proximal margin, 1 short seta, and 1 robust seta subapically. Distribution. Korea (south coast), China . Remarks. Ren noted that Byblis longiflagelis is morphologically similar to B. orientalis by the following features: (1) antenna 2 elongate, overreaching body end; (2) telson trapezoid ( Ren, 2006 ). However, B. longiflagelis is distinguished from B. orientalis (different characters of B. orientalis in brackets) by the following features: (1) lower eyes located on ventral corner of anterior cephalic lobe (vs. located on distal margin of anterior cephalic lobe); (2) coxae 1 - 3 angled anterodistally, ventral margins serrated (vs. roundish anterodistally, ventral margins smooth); (3) coxa 4 posterior tooth moderately attenuated and subacute (vs. posterior tooth not attenuated); (4) pereopods 3, 4, dactyli longer than propodi (vs. dactyli subequal or short- er than propodi); and (5) pereopod 7, carpus subequal to propodus in length (vs. carpus shorter than propodus in length) ( Ren, 2006 ). In Korea , B. japonica is already known in the genus. However, B. longiflagelis can be easily distinguished from B. japonica as follows: (1) antenna 2 longer than body length (vs. shorter than body length), (2) coxae 1 - 3 ventral margins serrated (vs. ventral margins smooth). Our Korean specimens are in good agreement with the description by Ren (2006) .