Sinocorophium hangangense, Kim, Young-Hyo, 2012

Kim, Young-Hyo, 2012, Sinocorophium hangangense sp. n. (Crustacea, Amphipoda, Corophiidae), a new species from Korea, with a key to the genus Sinocorophium, ZooKeys 181, pp. 53-65 : 55-61

Sinocorophium hangangense sp. n. Figs 25

Korean name:

Han-gang-baem-yeop-sae-u, new

Material examined.

Holotype, adult male, 12.2 mm, NIBRIV0000245089, Gongreung stream, Songchon-ri, Gyoha-eup, Paju-si, Gyeonggi-do, Korea, 37°45'10'N, 126°42'20'E, C.M. Lee and Y.H. Kim, 2 November 2002. Paratype, adult female, 11.0 mm, NIBRIV0000245090, same station data; one male, 11.5 mm and one female, 10.5 mm, CMNC 2012-0002, same station data; three females, 8.7-10.2 mm, DKU 201203, same station data.

Additional material examined.

2 males, same locality as holotype, C.M. Lee, 30 September 2006; 2 males, 3 females, same locality as holotype, C.M. Lee, 4 November 2006; 5 males, 4 females, same locality as holotype, C.M. Lee, 3 May 2008.

Coloration in alcohol.

Body yellowish grey; antennae to urosomites with light brownish reticulate pattern dorsally, especially pereonites with 2 longitudinal rows of light brown lines dorsally (Fig. 2).

Description.

Holotype, adult male, NIBRIV0000245089.

Body (Fig. 3A) 12.2 mm long, head longer than pereonite 1, rostrum (Fig. 3B) pointed distally, triangular in dorsal view. Eye invisible in alcohol. Cephalic lobe sharply produced. Pereonites 1-2 subequal in length, shorter than pereonite 3. Coxae flat dorsoventrally, except coxa 1, much shallower than pereonites. Urosomites 1-3 separate.

Antenna 1 (Figs. 3B, 3C) weakly setose, subequal in length to head and pereonites 1-4 combined; peduncular article 1 rectangular, distinctly narrowed distally, medial margin irregularly serrated when viewed dorsally, ventrodistal corner with 1 small robust seta and 1 penicillate seta, distal half of ventral margin with 8 setae; length ratio of peduncular articles 1-3 = 1.00: 0.41: 0.31; flagellum 13-articulate, shorter than peduncle, several articles bearing club-shaped, small aesthetascs ventrodistally.

Antenna 2 (Figs. 3A, 3D) massive, nearly twice as long as antenna 1; peduncular article 2 with large curved and sharply pointed gland cone; peduncular article 3 longer than wide; peduncular article 4 1.23 × article 5, with a row of tubercles ventromedially and a ventrodistal large tooth; peduncular article 5 rectangular, with a row of tubercles ventromedially; flagellum biarticulate, proximal one with a row of tubercles, 0.56 × peduncular article 5, distal one short, about 0.2 × proximal one, with 2 unequal setae apically.

Lower lip (Fig. 3E) inner lobe subovate, coalescent proximally, rounded apically; mandibular process small and blunt; both lobes covered with patch of pubescence medially.

Left mandible (Fig. 3F) well developed, incisor and lacinia mobilis produced inward, bluntly tridentate; accessory setal row with 2 curved, finely pectinate blades; molar well developed, massive, truncate; palp biarticulate, proximal segment shorter than distal, with 1 simple seta apically and 1 sparse plumose seta subapically, distal segment slender, with pubescence medially and long plumose seta apically.

Maxilla 1 (Fig. 3G) inner plate unknown; outer plate armed with 7 setal-teeth (simple or serrulate) apically; palp biarticulate, proximal segment short, wider than long, distal one extending beyond end of outer lobe, with row of 7 simple setae and 2 unequal robust setae apically, with row of 7 setae subapically.

Maxilla 2 (Fig. 3H) inner plate with longitudinal row of pinnate setae on inner margin, apical margin with 2 rows of simple or pectinate setae; outer plate extending beyond end of inner one, inner distal and apical margins with simple or plumose setae.

Maxilliped (Fig. 3I) inner plate slender and elongate, inner surface covered by pubescence, basal portion with transverse row of about 22 plumose setae, apical margin with 3 unequal robust setae, 1 pinnate and 2 simple setae, respectively; outer plate not reaching distal end of article 2 of palp, inner margin straight, densely setose, with 1 long pinnate seta distally, outer margin pubescent, curved convexly; palp 4-articulate, proximal article with 2 long plumose setae on outer margin, article 2 elongate, more than twice length of proximal one, inner margin densely setose, outer margin with 4 simple setae distally, article 3 subrectangular, with rounded distal corner, surrounded by setae distally, 0.34 × article 2, distal article short, 0.33 × article 3, with apical setae.

Gnathopod 1 (Fig. 4A) subchelate; coxa elongate-ovate, much longer than wide, ventral margin rounded with 3 long plumose setae, anterior margin with 6 setules; basis as long as carpus, anterior margin straight, unarmed, posterodistal corner with unequal setae; ischium quadrate, with long pinnate setae ventrodistally; merus short, subtriangular, with long pinnate setae ventrodistally; carpus slightly narrowing distally, anterior margin with 5 simple setae, distomedial corner with transverse row of 6 simple setae, posterior margin with 2 rows of pinnate setae; propodus subrectangular, posterior margin concave, 0.74 × carpus, anterior and medial portions with pectinate setae, posterior margin with pinnate and simple setae, palm transverse, slightly convex, lined with row of bifid spinules; dactylus falcate, almost fitting palm.

Gnathopod 2 (Fig. 4B) simple; coxa small, wider than long; basis subrectangular, posterodistal margin with cluster of simple setae; ischium flat, depressed; merus convexly curved posteriorly, with 2 rows of long pinnate setae along posterior margin and medial portion; carpus isosceles triangle in shape, strongly widening distally, with several pinnate setae posterodistally; propodus weakly narrowing distally, 1.57 × carpus, both margins with unequal simple setae, proximal half of medial portion with oblique row of pinnate setae; dactylus long and falcate, curved concavely, inner margin with row of setules.

Pereopod 3 (Fig. 4C) coxa small, wider than long; basis weakly expanded medially, anterior margin with 5 setules, distal half of posterior margin with simple setae; merus slightly widening distally, 1.24 × propodus; carpus rather elongated, 0.69 × merus; dactylus simple, 0.52 × propodus.

Pereopod 4 (Fig. 4D) similar to pereopod 3.

Pereopod 5 (Fig. 4E) coxa depressed, much wider than long, slightly concave midventrally, narrowing distally; basis slightly widened medially, anteromarginally with row of setules, posteromarginally with sparse setae; merus widening distally, both margins with unequal simple setae; carpus with 2 oblique rows of 5 proximal and 8 distal robust setae respectively, subequal in length to propodus; dactylus short.

Pereopod 6 (Fig. 4F) similar to pereopod 5, but about 1.3 × longer; basis more greatly expanded posteriorly, with a row of setules and plumose setae; merus slightly widening distally, both margins with simple setae, posterodistally with 1 plumose seta; propodus slender, rectangular, 1.13 × carpus; dactylus about 0.5 × propodus.

Pereopod 7 (Fig. 4G) elongate, much longer than either pereopod 5 or 6; coxa small, ventral margin convexly rounded, with 4 setules; basis elongate-ovate, moderately expanded anteroposteriorly, densely setose along both margins with long plumose setae; ischium to propodus linear and rectangular; length ratio of articles 2-7 = 1.00: 0.31: 0.67: 0.48: 0.75: 0.36.

Urosomites 1-3 (Fig. 5A) separate; urosomite 1 longest, widest in middle when viewed dorsally, urosomite 2 longer than 3, nearly rectangular, posterodistal margins rounded in dorsal view; uropods 1-3 arising laterally.

Uropod 1 (Fig. 5A) slightly extending beyond end of uropod 2; peduncle rectangular, 1.84 × outer ramus, ventrodistal process present, triangular, blunt, lateral margin with row of simple setae, medial one with 3 robust setae; outer ramus slightly longer than inner, lateral margin with 6 robust setae, medial one with 5 robust setae, including 2 subdistal robust setae; inner ramus slightly curved medially.

Uropod 2 (Fig. 5A) peduncle slightly longer than rami, with triangular ventrodistal process, apicodistal robust setae and cluster of setae; rami subequal in length, with robust setae marginally.

Uropod 3 (Fig. 5A) uniramous, peduncle short, broader than long, 0.78 × ramus; ramus subelliptical, narrowing distally, margins with unequal simple setae, with apical setae.

Telson (Fig. 5A) fleshy, thickened, grooved centrally, subtriangular, with truncate corners, broadest in middle, dorsolaterally with 2 penicillate setae and 1 setule.

Paratype, female (sexually dimorphic characters), 11.0 mm, NIBRIV0000245090.

Body (Fig. 5B) similar to male including antenna 2, but rostrum (Fig. 5C) weaker; antenna 1 (Fig. 5D) peduncular article 1 without medial serrations, article 3 rather short; antenna 2 (Fig. 5E) subsimilar to that of male, but less robust and shorter, peduncular article 4 with 1 ventromedial robust seta.

Remarks.

Bousfield and Hoover (1997) divided Sinocorophium into two groups, a relatively ancestral and a more derived subgroup through a numerical taxonomic analysis. According to this classification, the new species belongs to the derived subgroup. Some characteristics which relate to this group include non sexual dimorphic antenna 2, convex palm of the gnathopod 1, short carpi of pereopods 3-4 and short ramus of the uropod 3 (Table 1). However, the new species shows more similarity with the ancestral subgroup in having an elongate-ovate ramus of uropod 3 which is longer than the peduncle. The new species is distinguished from its congeners by having a row of slender setae and not robust setae on the lateral margin of the peduncle of uropod 1. These are unique morphological systematic statuses among the more derived subgroup which is sexually subsimilar in antenna 2. Ecologically the new species inhabits lower stream regions with lowered salinity, while related congeners except Sinocorophium intermedium and Sinocorophium minutum inNorth Vietnam are mainly abundant in shallow subtidal and intertidal mudflats. Among the derived subgroup species, the new species is more similar to Sinocorophium alienense of the northeast Pacificthan to the geographically closer sinocorophiid amphipods in the Far East. These two species have several characteristics in common: 1) prominent ventromedial teeth row on peduncular articles 4-5 and first flagellum of male antenna 2; 2) inner ramus of uropod 1 curved medially and shorter than outer one; 3) antenna 2, posterodistal tooth of peduncular article 4 unidentate; 4) basis of pereopod 5 bearing posteromarginal setae. However, the new species is distinguished from Sinocorophium alienense (different characters of Sinocorophium alienense in brackets) by the combination of the following features: 1) peduncular article 1 of male antenna 1 with ventral simple setae (with pinnate setae); 2) peduncular article 1 of antenna 1 about 2.3 × article 2 (peduncular article 1 subequal in length to article 2); 3) peduncular article 1 of antenna 1 with serrated medial margin (with smooth margin); 4) each lobe of telson with mid-lateral 1 simple and 2 penicillate setae, respectively (unornamented).

Etymology.

Named for the type locality, Gongreung stream, which is a small tributary on the lower reaches of the Han River in Gyeonggi-do, Korea. The Korean word “Gang” means river.

Habitat.

The new species is found in brackish water regions, but it may inhabit intertidal regions, are downstream of the type locality.

Distribution.

Songchon-ri, Gyoha-eup, Paju-si, Gyeonggi-do, Korea.

Key to the species of Sinocorophium