Elasmopus puteus, Chandani Appadoo, 2003

Chandani Appadoo, 2003, The Genus Elasmopus (Crustacea: Amphipoda: Melitidae) from Mauritius (Indian Ocean) with Description of Five New Species, Records of the Australian Museum 55, pp. 61-84 : 71

Elasmopus puteus n.sp.

Figs. 7, 8

Type material. HOLOTYPE: 3, 2.8 mm, from mixture of the algae Pocockiella variegata , Sargassum sp. , Amphiroa sp. and Cymodocea sp. , Bain Boeuf (19°59'S 57°36'E), 16 Jun. 1999, AM P60546. PARATYPES: 13 and 3♀, same data as holotype, AM P60547; 13, 1♀ from the algae Padina sp. , Digenia simplex , Turbinaria ornata and Dictyota divaricata, Roche Noires (20°6.2'S 57°44.5'E), 16 Dec. 1999, AM P60548.

Additional material examined. 233 from Sargassum sp. and Turbinaria ornata, Bain Boeuf , 15 May 1998. 13 from Sargassum sp. , Roche Noires, 20 Jan. 1999. 83, 29♀, 9 juv., from mixture of the algae Pocockiella variegata , Sargassum sp. , Amphiroa sp. and Cymodocea sp. , Bain Boeuf, 16 Jun. 1999. 4♀ from mixture of Sargassum sp. , Turbinaria ornata and Pocockiella variegata, Bain Boeuf , 12 Oct. 1999. 1♀ from mixture of Padina sp. , Pocockiella variegata and coral rubble, Flic-en-Flac, 10 Dec. 1999. 13, 2♀ from Padina sp. , Digenia simplex , Turbinaria ornata and Dictyota divaricata, Roche Noires , 16 Dec. 1999. 13, 1♀ from mixture of the algae Padina sp. , Turbinaria sp. , Sargassum sp. , Digenia sp. and Pocockiella variegata, Bain Boeuf , 24 Jan. 2000. 2♀ from mixture of the algae Sargassum sp. , Digenia simplex , Centroceras clavulatum and Ulva reticulata, La Cuvette (20°00'S 57°34.2'E), 25 Jan. 2000.

Description. Male: Length, 3 mm. Head, with subocular notch; eyes, small subround, with clear ommatidia. Antenna 1, peduncle articles sparsely setiferous; peduncle article 2, 0.6× article 1; article 3, 0.5× article 1; accessory flagellum 1-articulate; primary flagellum 13-articulate. Antenna 2, peduncle poorly setiferous; article 5, 0.9× article 4; flagellum 6-articulate, the terminal article rudimentary. Mandible, palp article 2 longest, with 1 medial and 2 distal setae; article 3 falcate, 0.7× article 2, with comb row of setae and 2 long terminal setae. Maxilla 1, inner plate with 2 terminal plumose setae. Labium, mandibular lobes rounded; outer plate with a blunt stout seta on inner margin. Maxilliped, palp article 3 with a small distal protuberance. Gnathopod 1, coxa produced distally, 1.5× as long as broad, with very short setae on distal margin; basis 2.3× as long as broad, posterior margin with a group of long setae; carpus and propodus subequal and each with long setae on the inner face of the anterior margin; propodus with palm almost transverse with a stout defining robust setae. Gnathopod 2, coxa 1.6× as long as broad, distal margin with very short setae; basis 3.2× as long as broad; carpus cup-shaped, twice as broad as long; propodus slender, subpyriform, twice as long as broad, 4× the length of carpus, palm oblique, posterior margin poorly setiferous, with a small subtriangular process on the inner subdistal face and a medial excavation forming a pit into which fits the tip of the dactylus; dactylus evenly curved, about half length of propodus. Pereopods 3–4, basis 3.3× as long as broad; propodus subequal to carpus; dactylus subdistally constricted. Pereopod 5, basis subquadrate tapering distally, posterior margin weakly crenulate with short setae. Pereopod 6, basis subquadrate, posterior margin weakly convex, crenulate and with short setae. Pereopod 7, basis strongly expanded, posterior margin very convex, crenulate with small setae. Epimeron 1 rounded. Epimera 2–3, produced into a weak posterodistal tooth and with a row of robust setae on the anterodistal margin. Uropod 1, rami subequal to each other and to peduncle. Uropod 2, peduncle 0.7× inner ramus; inner ramus 1.1× outer ramus. Uropod 3, peduncle subequal to inner ramus; inner ramus 0.8× outer ramus; inner ramus with lateral and terminal robust setae; outer ramus with lateral robust setae and a group of terminal robust setae and 1 long slender seta.Telson, deeply cleft; apices notched, outer tooth more developed than inner tooth, each with 1 long and 2 short robust setae.

Female secondary sexual characters: length, 2.5 mm (ovigerous). Gnathopod 1, similar to that of male but lacking long setae on the anterior margin of the carpus and propodus. Gnathopod 2, coxa 1.9× as long as broad; basis 3× as long as broad; carpus 1.4× as long as broad; propodus slender, 2.3× as long as broad, palm oblique, almost straight, defined by two robust setae; dactylus shorter than that of the male, overlapping the inner face of the propodus, but not fitting into a pit.

Remarks. In its general form this species resembles Elasmopus gracilis Schellenberg, 1938 but differs in the male gnathopod 2. The propodus posterior margin is sinuous (evenly convexin E. gracilis ), lacks the dense setation of E. gracilis and has a distinct triangular process on the inner face, which is lacking in E. gracilis . In addition, the dactylus is much shorter than in E. gracilis and fits into a distinct pit.

This species can be distinguished from the other species of Elasmopus in Mauritius by the following combination of characters: its poorly setiferous antennae, coxae and propodus of gnathopod 2, and the largely expanded basis of pereopod 7 which is almost as broad as long. It is also a very small species.

Type locality. Bain Boeuf , Mauritius .

Distribution. Only known from Mauritius.

Etymology. From puteus —pit, referring to the pit on the inner face of the posterior margin of the male propodus into which fits the tip of the dactylus.