Paracorophium angsupanichae, Wongkamhaeng, Koraon, Nabhitabhata, Jaruwat & Towatana, Prawit, 2015

Wongkamhaeng, Koraon, Nabhitabhata, Jaruwat & Towatana, Prawit, 2015, Corophiine amphipods of the genera Chelicorophium and Paracorophium from the lower Gulf of Thailand (Crustacea, Amphipoda, Corophiidae, Corophiinae), ZooKeys 505, pp. 35-50 : 37-38

Taxon classification Animalia Amphipoda Corophiidae

Paracorophium angsupanichae sp. n. Figs 2, 3, 4, 5, 6

Material examined.

Holotype. ♂, THAILAND, Lower Gulf of Thailand, Middle Songkhla Lake (7°28'36"N, 100°24'6"E), 23 October 2014, leg. K. Wongkamhaeng, PSUZC-CR-0350. Allotype, ♀ collected with holotype; PSUZC-CR-0351; Paratypes, collected with holotype PSUZC-CR-0352 (5♂; 5♀) and ZMB28473 (3 ♂;3♀)

Description.

Based on male holotype. Body length 1.75 mm (from tip of rostrum to apex of telson). Body compressed, smooth, urosomites 1-3 free. Head, lateral cephalic lobe rounded. Antenna 1 sparsely setose, short, one third of body length, ratios of peduncular articles 1-3 5:6:3; accessory flagellum absent; primary flagellum 7-articulate, bearing 4-6 aesthetascs. Antenna 2, sparsely setose; flagellum 6-articulate. Upper lip (labrum) symmetrically incised distally. Lower lip (labium), inner lobes well developed. Mandible, both similar, left incisor 3-dentate, right incisor 4-dentate; left and right lacinia mobilis armed with 3 and 4 teeth respectively; ratios of palp article 1-3 5:8:6. Maxilla 1, inner plate short; outer plate with 9 bifid robust setae; palp 2-articulate, second article with 9 distal robust setae. Maxilla 2, inner lobe with distal and marginal plumose setae; outer lobe with 13 fine setae. Maxilliped, inner plate exceeding palp article 1, oblique, with 8 basal setae, 7 apical plumose setae and 2 apical robust setae; outer plate not reaching apex of palp article 2, with 9 marginal robust setae and 2 fine apical setae; palp 4-articulate; ratios of peduncular articles 1-4 3:7:4:2.

Pereon. Gnathopod 1 subchelate, smaller than gnathopod 2; coxal plate trapezium-shaped, produced anteriorly with 7 fine setae on anteroventral corner and 2 robust setae on posterior margin; length ratio of articles from basis to dactylus 3:1:1:3:2:1; basis slender, broader distally, with anterodistal setae and posteromarginal setae; ischium short, subrectangular; merus subtriangular with posteromarginal setae; carpus long, with plumose setae on both margins; propodus subtriangular, palm oblique with a defining robust seta. Gnathopod 2 chelate; coxal plate subquadrate; length ratio of articles from basis to dactylus 8:3:7:6:12:6; basis robust, expanded distally; merus subtriangular, distal angle produced with a group of very long plumose setae on anterior margin; carpus medially expanded, bearing dense setae on posterior margin; propodus suboval, narrowing distally with a weak subdistal excavation on posterior margin, anterior margin sparsely setose, palm obtuse with subrectangular distomedial elevation bearing 4 robust setae; dactylus overlapping palm, expanded medially with 3 fine setae and 1 distal seta. Pereopod 3 slender; coxal plate deeper than long, slightly expanded ventrally, beset with marginal setae; length ratio of articles from basis to dactylus 6:2:6:2:5:2; basis slender; ischium short; merus slightly produced anterodistally, anterior margin lined with 9 long setae and short posterodistal setae; carpus and propodus slender, lined with marginal setae on both sides; dactylus curved. Pereopod 4 similar to pereopod 3; length ratio of articles from basis to dactylus 6:2:4:2:3:1; basis slender, with long fine setae on posterior margin; merus slightly produced anterodistally; carpus suboval with a weak subdistal excavation, with setae on both margins; propodus long and narrow, sparse setae; dactylus long and thin with one seta. Pereopod 5-7 progressively longer, in the length ratio 2:3:4. Pereopod 5 coxa bilobed; length ratio of articles from basis to dactylus 8:2:4:3:4:1; basis oval, sparsely setose; merus and carpus subequal with anteromarginal setae; propodus slender with 3 marginal robust setae; dactylus curved. Pereopod 6 coxa bilobed; length ratio of articles from basis to dactylus 9:2:4:4:5:1; basis oval, posterodistally excavated, lined with 10 plumose setae; merus subrectangular with a median robust seta and distal setae; carpus subrectangular with distal robust setae; propodus slender with 3 marginal setae; dactylus long and curved. Pereopod 7 coxa subtriangular; basis suboval, posterodistally excavated; merus - propodus slender with marginal and distal robust setae; dactylus tapering to pointed tip.

Pleon.Pleopods 1-3 well developed; peduncles subrectangular with 2 retinaculae, longer than broad; rami unequal, inner ramus longer than outer ramus. Epimeron 1-3 subquadrate; epimeron 2 bearing 7 plumose setae. Uropod 1 not extending beyond ends of other uropods; peduncle longer than rami, fringed with robust setae, peduncular apex bearing a posteroventral process; outer and inner ramus subequal, both rami lined with a row of robust setae, distal margins rounded and bearing several robust setae. Uropod 2 peduncle subequal to rami; outer ramus slightly longer than inner one, both rami with apical robust setae and outer ramus bearing medial robust setae. Uropod 3, peduncle subequal to rami subequal to outer ramus, which is slightly longer than inner one, bearing 4 apical setae; inner ramus with 2 fine apical setae and 1 robust seta. Telson subtrapezoidal, broader than long, each distal margin with distal spine.

Female (allotype). Total body length 2.6 mm (from tip of rostrum to apex of telson). Sexually dimorphic characters: Antenna 1 flagellum with 5 articles, last 2 articles bearing aesthetascs. Gnathopod 2 coxa much deeper than wide; basis elongate, expanded distally; merus subtriangular with a long plumose setae on anterior margin; carpus subrectangular, bearing long plumose setae on posterior margin; propodus elongate with posterior plumose marginal setae, palm poorly developed with 2 robust setae; dactylus curved.

Etymology.

The species is named in honor of Professor Dr. Saowapa Angsupanich of Prince of Songkla University, Thailand, who contributed to the study of the ecosystem in Songkhla Lake.

Remarks.

Paracorophium angsupanichae sp. n. is characterized by male gnathopod 2 chelate and shares this character with Paracorophium chelatum in the Palau Islands, in the southern Pacific Ocean, east of the Philippines. Both amphipods inhabit freshwater environments above tidal influence. However, Paracorophium chelatum has the following characters ( Karaman 1979): 1) its maxilliped lacks the distinctive rows of long setae on the basal segment (present in Paracorophium angsupanichae ), 2) its male gnathopod 2 palm is smooth (palm is obtuse with subrectangular distomedial elevation bearing 4 robust setae), and 3) its urosomites 1-2 are fused (urosomites 1-3 are free in Paracorophium angsupanichae ).