Sinocorophium dongtanense Ren and Liu, 2014

Kim, Kyung-Won & Kim, Jun-Haeng Heo and Young-Hyo, 2023, A new record of the species Sinocorophium dongtanense (Crustacea: Amphipoda: Corophiidae) from Korean waters, with comparison to Sinocorophium homoceratum, Journal of Species Research 12 (4), pp. 286-293 : 287-291

Sinocorophium dongtanense Ren and Liu, 2014

( Figs. 1-3 ) ṣẖ"ẹăNjș (ṳḡ)

Sinocorophium dongtanense Ren and Liu, 2014 , 96, figs. 1 - 3.

Sinocorophium homoceratum : Ko et al., 2017, 277, figs. 2 - 6; Heo and Kim, 2017, 160, figs. 5, 6.

Material examined. 4♂, 37$ Watan stream, Ibam-ri , Beopseong-myeon, Yeonggwang-gun, Jeollanam-do, Korea 35°20′15.76″N, 126°26′2.04″E, 01 April 2020 ; 2♂, 16$ Jujin stream, Yonggi-ri , Simwon-myeon, Gochang-gun, Jeollabuk-do, Korea, 35°31′48.35″N, 126°35′44.12″E, 02 April 2020 ; 1♂, 9$ Watan stream, Ibam-ri , Beopseong-myeon, Yeonggwang-gun, Jeollanam-do, Korea 35°20′ 15.76″N, 126°26′2.04″E, 31 August 2020 . The specimens were collected by KES.

Description. Adult male, body ( Figs. 1A , 2) depressed, 12.6 mm long (NIBRIV0000904521). Head ( Fig. 2B) longer than pereonite 1; cephalic lobe produced; eye in- visible in alcohol. Length ratio of pereonites 1 - 7 = 1.00: 1.47: 1.46: 1.92: 2.10: 1.96: 1.67. Coxae flat dorsoventrally, much shallower than pereonites, except coxa 1. Pleonites 1 - 2, posteroventral corners rounded, with plumose setae posterolaterally; pleonite 3 slightly shorter than pleonites 1 and 2 combined, with simple setae. Urosomites 1 - 3 separate.

Antenna 1 ( Fig. 2C) much shorter than antenna 2; peduncle longer than flagellum, peduncular article 1 subrectangular, with irregularly serrulate medially in dorsal view, irregularly serrulate ventrally with 1 small robust seta ventrodistally and unequal simple setae ventrally, length ratio of peduncular articles 1 - 3 = 1.00: 0.41: 0.27; flagellum 16 - 20 articulate, with each article with simple short setae.

Antenna 2 ( Fig. 2D) massive, peduncle stout; peduncular article 2 with 2 pointed unequal gland cones ventrodistally; peduncular article 4 characteristic in form, long and stout, 1.14 times as long as article 5, with 2 lows of tuber- cles medially, 2 strong teeth ventrodistally; peduncular article 5 cylindrical, with 2 teeth anteromedially; length ratio of peduncular articles 2 - 5 = 1.00: 1.72: 5.31: 5.29; flagellum biarticulate, proximal one 0.62 times as long as peduncular article 5, with 6 small teeth on ventral margin, distal one short, about 0.14 times as long as proximal one, surrounded by setae apically.

Gnathopod 1 ( Fig. 2E) transverse; coxa elongate anteriorly, with 3 long plumose setae distally, anterior margin with 5 - 8 unequal setae; basis with 1 - 3 long simple setae posterodistally; ischium subrectangular, with long plumose setae ventrodistally; merus short, with plumose setae ventrodistally; carpus with 2 - 3 simple setae midanteriorly, distal corner with a transverse row of simple setae, posterior margin with 2 rows of plumose setae; propodus subrectangular, palm lined with rows of bifid spinules; dactylus falcate, nearly fitting to palm; length ratio of 2 - 7 articles = 1.00: 0.26: 0.27: 1.02: 0.64: 0.22.

Gnathopod 2 ( Fig. 2F) simple; coxa small; basis with 3 - 5 long simple setae posterodistally; merus convexly curved posteriorly, with 2 rows of long plumose setae along posterior margin and medial portion; carpus isos- celes triangle in shape, with several simple and plumose setae posterodistally; propodus both margins with simple setae, proximal half of medial region with a curved row of plumose setae; dactylus long and falcate; length ratio of 2 - 7 articles = 1.00: 0.15: 0.96: 0.81: 1.25: 0.83.

C B E A D F G H

Pereopod 3 ( Fig. 2G) simple; basis subrectangular; merus slightly widening distally; propodus thin and long, 0.73 times as long as merus; dactylus slender and falcate; length ratio of 2 - 7 articles = 1.00: 0.35: 0.52: 0.40: 0.48: 0.35.

Pereopod 4 ( Fig. 2H) similar to pereopod 3, but basis slightly more setose.

Pereopod 5 ( Fig. 3A ) much shorter and different struc- ture than pereopod 4, coxa narrowing posteriorly; basis slightly widened anteriorly, anteromarginally with several setae, posterior margin with 8 plumose setae; merus widening distally, both margins with plumose setae; carpus subtriangular, with 2 oblique rows of 5 proximal and 10 distal robust setae respectively; propodus subequal in length to merus; dactylus short. length ratio of 2 - 7 articles = 1.00: 0.30: 0.60: 0.28: 0.28: 0.15.

Pereopod 6 ( Fig. 3B ) similar to pereopod 5, but longer; basis with a row of plumose setae posteriorly; merus anterior margin with a row of unequal plumose setae; carpus subtriangular, with 2 oblique rows of 5 proximal and 8 distal robust setae respectively; propodus slender; dactylus short; length ratio of 2 - 7 articles = 1.00: 0.22: 0.69: 0.31: 0.34: 0.17.

Pereopod 7 ( Fig. 3C ) elongate, greatly longer than others; basis elongate-ovate, 0.46 times wider than long, densely setose along both margins with long plumose setae; length ratio of 2 - 7 articles = 1.0: 0.30: 0.66: 0.62: 0.84: 0.38.

Urosomites 1 - 3 ( Fig. 3D ) separate; urosomite 1 longest, widest and slightly curved dorsally; uropods 1 - 3 aris- ing laterally.

Uropod 1 ( Fig. 3D ) extending beyond end of uropod 2; peduncle much longer than rami, 1.85 times as long as outer ramus, lateral margin with 13 short setae, medial margin with 4 robust setae; outer rami 1.30 times longer than inner.

Uropod 2 ( Fig. 3D ), peduncle slightly longer than rami, with apicodistal robust seta and cluster of setae laterally; rami subequal in length.

Uropod 3 ( Fig. 3D ) uniramous, peduncle subtrapezoi- dal, subequal to ramus; ramus ovate, margins surrounded by simple setae.

Telson ( Fig. 3D ) fleshy, thickened, truncate distally, with 2 rounded lobe dorsolaterally.

Adult female, similar to male, body ( Fig. 3E ) 11.6 mm long. Head ( Fig. 3F ) similar to that of male, but rostrum wider and longer, beyond cephalic lobe.

Antenna 1 ( Fig. 3G ) similar to that of male, but more setose, smooth; peduncular article 1 rectangular, with unequal simple setae ventrally and a robust seta posterodistally, without lows of teeth; length ratio of peduncular articles 1 - 3 = 1.00: 0.53: 0.36; flagellum 13 - 16 articulate, each article with simple short setae.

Antenna 2 ( Fig. 3H ) similar in shape, but stouter and shorter than that of male, especially peduncular articles 3 and 4; length ratio of peduncular articles 2 - 5 = 1.00: 1.41: 3.15: 2.63; flagellum biarticulate, proximal one 0.51 times as long as peduncular article 5, distal one short, 0.22 times as long as proximal one.

Molecular data. CO1 gene sequences (GenBank accession numbers OQ996608, OQ998653, OQ998654, OR 048101, OR048102) were obtained from five S. dontanense specimens. The sequences were aligned and compared with sequences from S. hangangense (OQ943924, OQ970180), S. jindoense (OQ991265, OQ992550), and S. sinensis (OQ991369, OQ991370) ( Table 1). Intra-specific variation of the CO1 gene sequence of S. dontanense ranged between 0 and 1.2%, while inter-specific variation ranged from a low of 22.8% ( S. hangangense and S. jindoense ) to a high of 26.7% ( S. dontanense and S. jindoense ) ( Fig. 5 , Table 2).

Remarks. It seems that there has been a mistake in the identification of specimens previously recorded as S. homoceratum ( Yu, 1938) in Korea ( Heo and Kim, 2017; Ko et al., 2017). Upon rechecking the sample descriptions and specimens used in previous studies ( Fig. 4 ), it was found that these specimens had the characteristics of S. dongtanense Ren and Liu, 2014 , which is morphologically similar to S. homoceratum , but has distinct differences, such as two rows of teeth on the medial surface of peduncular article 4 of antenna 2. To confirm this, the COI molecular sequences of both previously identified and newly identified samples of S. dongtanense and other Sinocorophium species in Korea were compared and analyzed, along with related genus data from the NCBI ( Fig. 5 ). The new specimens accord with the original description given by Ren and Liu, 2014, with some slight differences in certain characteristics, such as the length of antenna 1 in males and the number of teeth on peduncular article 4 of antenna 2 in females. Through this study, there are four species of the genus Sinocorophium in Korean waters.

Habitat. The new recorded species is found in brackish estuary with a water temperature of 15.38℃, salinity of 6.45 PSU, and pH 6.9. Sediment is composed of gravel and sand.

Distribution. China, Korea (Yellow Sea).

Figures

Fig. 1. Sinocorophium dongtanense Ren and Liu, 2014. A, adult male, 12.4 mm, habitus; B, adult female, 11.7 mm, habitus.

Fig. 3. Sinocorophium dongtanense Ren and Liu, 2014. A, pereopod 5; B, pereopod 6; C, pereopod 7; D, urosomites. Adult female, 11.71 mm: E, habitus; F, head(dorsal view); G, antenna 1 (medial view); H, antenna 2 (left, medial view). Scale bars:A-H=1.0 mm.

Fig. 5. Neighbor-Joining (NJ) tree of mtDNA COI sequences from four Korean Sinocorophium species based on maximum likelihood(ML) genetic distances.

Fig. 4. Sinocorophium homoceratum, peduncular article 4 of antenna 2 (MABIK CR00240676) from MABIK, analyzed by Ko et al., 2017. A, dorsal view; B, medial view.