Elasmopus palu, 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 : 65

Elasmopus palu n.sp.

Fig. 3

? Elasmopus ecuadorensis hawaiensis .– Ledoyer, 1978: 269, fig. 27.

Type material. HOLOTYPE: 3, 2.5 mm (slides and carcass) from Padina , Pocockiella variegata and coral rubble, Flicen-Flac (20°16.5'S 57°21.7'E), 10 Dec. 1999, AM P60543. PARATYPES: 2♀♀, same data as holotype, AM P60542.

Description. Male: Length, 2.5 mm. Head, with subocular notch; eyes large, oval with well-developed ring of clear ommatidia surrounding a dark central core. Antenna 1, peduncle article 2 subequal to 1; article 3, 0.5× article 1; accessory flagellum 1-articulate; primary flagellum 14- articulate, the terminal article rudimentary. Antenna 2, article 5, 0.9× article 4; flagellum 7-articulate. Mandible, palp article 2 with 1 small medial and 2 distal setae; article 3 falcate, 1.2× article 2 with comb row of setae and 4 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 a blunt stout seta on inner margin. Maxilliped, palp article 3 with a small distal protuberance. Gnathopod 1, coxa 1.5× as long as broad, weakly produced anterodistally, distal margin with short setae; basis 2.3× as long as broad; propodus 1.2× carpus, palm defined by a stout robust seta. Gnathopod 2, coxa 1.8× as long as broad, distal margin with short setae; basis 2.8× as long as broad; carpus cup-shaped, twice as broad as long; propodus 3.7× carpus, 1.9× as long as broad, posterior margin densely setose, setae longest proximally but reducing in length sequentially towards distal end, palm a short shelf followed by a concavity, inner face of propodus with a small ridge bearing short robust and fine setae; dactylus about half length of propodus. Pereopod 3–4, coxa with short setae on distal margin; propodus posterodistal margin with 1 curved striate sabre seta and 1 straight robust seta. Pereopod 5–7, basis posterior margin castellate with short setae. Epimera 1–3, with a row of robust setae on the anterodistal margin. Epimeron 3, posterodistal margin with 2 teeth. Uropod 1, peduncle subequal to inner ramus; outer ramus 0.9× inner ramus. Uropod 2, outer ramus 0.8× inner ramus. Uropod 3, peduncle 1.3× inner ramus; inner ramus twice as long as broad, 0.6× outer ramus. Telson, cleft to about 75% its length, with notched and broadly sinuous apices, each with 2 robust setae.

Female secondary sexual characters: length, 2.9 mm (ovigerous). Gnathopod 1, similar to that of male but basis 2.5× as long as broad. Gnathopod 2, coxa 1.7× as long as broad; basis 3× as long as broad; carpus 1.4× as long as broad; propodus twice as long as carpus, 2.2× as long as broad, palm oblique, defined by a robust seta.

Remarks. Elasmopus palu n.sp. resembles E. lapu Myers (1985) , but differs in several ways: in E. palu , the distal margins of coxa 1 and 2 lack dense long setae, the flagellum of antenna 1 is 14-articulate (20-articulate in E. lapu ), the carpus of the male gnathopod 2 is less compressed and epimeron 3 has two teeth on the posterodistal margin, which are lacking in E. lapu . Elasmopus lapu reaches 5.5 mm whereas E. palu is only 2.5 mm in the male and 2.9 mm in the female. The species described by Ledoyer (1978) from Mauritius under the name Elasmopus ecuadorensis hawaiensis closely resembles E. palu . Similarities include the development of a tooth on the inner face of the posterior margin of the male gnathopod 2 propodus (better developed in Ledoyer’s figures) and a strong almost transverse palmar shelf, the presence of two small teeth on the posterodistal corner of epimeron 3, the unequal uropod 3 rami and the shape of the basis of pereopods 5–7. The only difference is the presence of long setae on coxae 1–2 of Ledoyer’s specimens and the precise allocation of this material must await further study.

Type locality. Flic-en-Flac , Mauritius .

Distribution. Mauritius.

Etymology. An anagram of “lapu” recording its close similarity to Elasmopus lapu Myers, 1985 .