Elasmopus spinidactylus Chevreux, 1907

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 : 74

Elasmopus spinidactylus Chevreux

Fig. 11

Elasmopus spinidactylus Chevreux, 1908: 486 , figs. 9, 10.– Walker, 1909: 336.– Schellenberg, 1938: 55.– Shoemaker, 1942: 13.–J.L. Barnard, 1965: 504.–J.L. Barnard, 1970: 136, figs. 81, 82.– Sivaprakasam, 1966: 104, fig. 8; 1968: 50, fig. 6g,h.– Ledoyer, 1972: 223, pl. 40.– Ledoyer, 1982: 482, fig. 183.– Myers, 1985: 108, fig. 86.–Appadoo & Steele, 1998: 639.

Material examined. 233, 8♀♀, 6 juv., from the alga Acanthophora spicifera, Souillac (20°31'S 57°30.7'E), 3 Feb. 1998. 533, 9♀, 3 juv., from a mixture of the algae Acanthophora spicifera , Amansia glomerata and Boodlea sp. , Souillac, 13 Aug. 1998. 233, 8♀, 2 juv., from mixture of the algae Gracilaria millardetii , Centroceras clavulatum , Digenia simplex and Acanthophora spicifera, Souillac , 10 Nov. 1998. 13, 1♀ from Acanthophora spicifera, Souillac , 25 Mar. 1999. 233, 3♀ from Acanthophora spicifera and Centroceras clavulatum, Souillac , 8 Apr. 1999. 13 from mixture of the algae Sargassum sp. , Ulva lactuca and Acanthophora spicifera, Souillac , 14 Oct. 1999. 1♀ from mixture of Digenia simplex and Sargassum densifolium, Rivière des Galets (20°30'S 57°27'E), 16 Nov. 1999. 13, 1♀, 5 juv., from a mixture of Amansia glomerata , Gracilaria millardetii , Sargassum sp. , Souillac, 14 Dec. 1999. 1♀, from a mixture of Digenia simplex , Centroceras clavulatum , Sargassum sp. , La Cuvette (20°00'S 57°34.2'E), 25 Jan. 2000. 13, 3♀, 2 juv., from a mixture of the algae Amansia glomerata , Jania adherens and Sargassum densifolium, Souillac , 10 Feb. 2000.

Description. Male: length, 5.2 mm. Head, with subocular notch; eyes large, oval with well-developed ommatidia. Antenna 1, moderately setiferous; article 2, 0.7× length article 1; article 3, 0.6× length of article 1; accessory flagellum 2-articulate; primary flagellum 16-articulate. Antenna 2, peduncle articles with long setae; article 5, slightly shorter than article 4; flagellum 7-articulate. Mandible palp article 2 with 1 medial seta and 4 long distal setae; article 3 falcate, 1.2× length of article 2, with combrow of setae and 3 long apical setae. Maxilla 1, inner plate with 2 terminal plumose setae and several fine setae on inner margin. Labium, with mandibular lobes acute; outer plate with blunt stout seta on inner margin. Maxilliped, palp article 3 with small protuberance at distal end. Gnathopod 1, coxa subquadrate, 0.8× as long as broad, distal margin with a patch of setae, the longest seta 0.7× length of coxa; basis 2.2× as long as broad with 1 seta on posterior margin; carpus 0.9× length of propodus; propodus 1.6× as long as broad, with two semicircular comb-rows of setae on inner face; palm defined by a short, stout, robust seta. Gnathopod 2, coxa subquadrate, about as long as broad; basis twice as long as broad; carpus reduced, 3.5× as broad as long; propodus 8× as long as carpus, 1.8× as long as broad, posterior margin strongly setose, produced distally into an outwardly deflected flat-topped, obtuse process, palm with a few stout robust setae and long slender setae; dactylus 0.7× length of propodus. Pereopod 3–4, propodus posterodistal margin with 1 large striate, sabre, locking seta and 1 normal robust seta; dactylus with small nipple-like processes and subdistally constricted. Pereopods 5–7, dactylus posterior margin with nipple-like processes Pereopod 5, basis subovoid. Pereopod 6, basis subquadrangular and produced posterodistally into a triangular lobe; Pereopod 7, basis posterior margin convex with short setae. Epimera 1–3, with weak posterodistal tooth. Uropod 1, peduncle 1.2× length of inner ramus; rami subequal. Uropod 2, peduncle shorter than inner ramus; outer ramus 0.8× inner ramus. Uropod 3, peduncle subequal to outer ramus; inner ramus three-quarter length of outer ramus; inner ramus with terminal robust seta, outer ramus with lateral and terminal robust setae. Telson, short, cleft to 50% its length, apices broad and truncate with 2 robust setae on each lobe.

Female secondary sexual characters: length, 5.2 mm (ovigerous). Gnathopod 1, coxa 1.2× as long as broad, distal margin with a patch of long setae about half length of coxa; other features similar to those of male gnathopod 1. Gnathopod 2, coxa subquadrate as long as broad; basis 2.7× as long as broad with 1 seta on posterior margin; carpus 1.5× as broad as long; propodus 1.8× as long as broad, similar to that of male but lacking posterodistal process, palm oblique, with short robust setae, distal margin densely setose; dactylus 0.7× length of propodus.

Remarks. Both males and females of Elasmopus spinidactylus are easily recognized by the nipple-like processes on the dactylus of P3–7. The females of this species have an enlarged propodus similar to that of the male.

Habitat. This species occurs mostly on red algae in Mauritius.

Type locality. Makapou Island , Gambier Archipelago .

Distribution. Madagascar, Mauritius, Chagos Archipelago, India, Fiji, Micronesia, Melanesia, Polynesia, Hawaii, Venezuela.