Elasmopus steelei, 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 : 78-83

Elasmopus steelei n.sp.

Figs. 13, 14

Elasmopus sp. 1 .–Appadoo & Steele, 1998: 639.

Type material. HOLOTYPE: 3, 3.3 mm from mixture of the algae Sargassum densifolium , Amansia glomerata , Jania adherens and Digenia simplex, Souillac (20°31'S 57°30.7'E), 14 Oct. 1999, AM P60550. PARATYPES: 333, 1♀, same data as holotype, AM P60551; 333, 7♀ from Sargassum densifolium and Amansia glomerata, Souillac , 4 Aug. 1999, AM P60552.

Material examined. 433, 4♀♀, 3 juv., from Sargassum densifolium and Ulva reticulata, Souillac , 3 Feb. 1998. 13 from the alga Gelidiella sp. , Flic-en-Flac, opposite Klondike Hotel (20°15.7'S 57°22'E), 12 May 1998. 233, from the algae Amansia glomerata and Boodlea sp. , Souillac, 13 Aug. 1998. 233, 2♀, from the alga Dictyota divaricata, La Cuvette , 28 Aug. 1998. 1533, 15♀, 6 juv., from the algae Amansia glomerata , Ulva reticulata , Acanthophora spicifera, Souillac , 25 Mar. 1999. 13, 1♀ from Sargassum sp. and Ulva reticulata, La Cuvette (20°00'S 57°34.2'E), 5 May 1999. 13, 8♀, 5 juv., from Sargassum densifolium and Amansia glomerata, Souillac , 4 Aug. 1999. 533, 2♀, 3 juv., from mixture of Sargassum densifolium , Amansia glomerata , Jania adherens and Digenia simplex, Souillac , 14 Oct. 1999. 433, 3♀, 4 juv., from mixture of Sargassum densifolium , Ulva reticulata , Amansia glomerata and Jania adherens, Souillac , 10 Feb. 2000.

Description. Male: length, 2.8 mm. Head, with subocular notch; eyes small and round. Antenna 1, densely setose; peduncle articles 1 and 2 subequal; article 3, 0.6× article 1; accessory flagellum 2-articulate, the terminal article vestigial; primary flagellum 20-articulate. Antenna 2, densely setose; article 5, 0.9× article 4; flagellum 9- articulate. Mandible palp, article 2, 1.4× article 1, with 1 medial and 2 distal setae; article 3 falcate, 1.1× article 2, with a comb row of setae and 2 long apical setae. Maxilla 1, inner plate with 2 plumose terminal setae and several fine marginal setae. 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 anterodistally produced, about as long as broad, distal margin densely setose, a few setae equal to the depth of the coxa; basis 2.4× as long as broad; carpus inner face densely setose, subequal in length to propodus; propodus inner face densely setose, palm defined by a robust seta. Gnathopod 2, coxa 1.2× as long as broad, distal margin with setae about half length of coxa; basis 2.6× as long as broad, anterodistal margin with stout robust setae; carpus cup-shaped, 1.8× as broad as long; propodus twice as long as broad, 4.5× length of carpus, posterior margin weakly sinuous and with dense rows of pectinate setae; dactylus elongate, nearly two thirds length of propodus, inner margin expanded at about a quarter its length. Pereopods 3–4, coxa distal margin with a strong group of setae about half length of coxa; basis 3× as long as broad; propodus posterodistal margin with 1 striate sabre seta and 1 normal robust seta; dactylus subdistally constricted. Pereopod 5, basis subquadrangular, posterior margin weakly crenulate and with short setae. Pereopod 6, basis subquadrangular, posterior margin weakly concave, weakly crenulate with short setae. Pereopod 7, basis subovate, posterior margin strongly convex, castelloserrate with short setae. Epimera 1–3, with a row of robust setae on anterodistal margin. Epimeron 1, subquadrate. Epimeron 2, slightly produced into a weak posterodistal tooth. Epimeron 3, subquadrate. Uropod 1, peduncle 1.3× rami; rami subequal. Uropod 2, peduncle subequal to outer ramus; outer ramus 0.8× inner ramus. Uropod 3, inner ramus 0.8× outer ramus and with terminal robust setae only; outer ramus 0.9× peduncle, with two groups of robust setae on the lateral margins and a group of robust and 2 slender apical setae. Telson, cleft to 75% its length; lobes notched, each lobe with 1 strong robust seta.

Variation with size. In younger males the robust setae on the distal end of the basis of gnathopod 2 are not well developed, the dactylus of gnathopod 2 is shorter and the medial expansion of the dactylus is weak.

Female secondary sexual characters: length, 2.3 mm (ovigerous). Gnathopod 1, coxa 1.3× as long as broad, distal margin with numerous short setae; basis 2.6× as long as broad; propodus 1.2× length of carpus, 1.9× as long as broad, palmar margin with a defining robust seta. Gnathopod 2, coxa 1.5× as long as broad; basis 3× as long as broad; carpus 1.5× as long as broad; propodus 2.1× as long as broad, palm defined by a stout robust seta; dactylus fitting palm.

Remarks. This species is superficially similar to E. ecuadorensis Schellenberg (see also J.L. Barnard, 1979), but differs in several ways. The male gnathopod 2 coxa bears long setae and the basis anterodistal margin has robust setae, both characters absent in E. ecuadorensis and the propodus has a weakly developed palmar protrusion (strongly transverse in ecuadorensis ). The propodus of pereopods 3–4 has a striate, sabre, locking seta (striate but lanceolate in E. ecuadorensis ). The posterior margin of the basis of pereopod 6 is concave in present material but straight to weakly convex in E. ecuadorensis and pereopod 7 basis is castellate in present material but weakly serrate in Elasmopus ecuadorensis . Elasmopus steelei also resembles E. lapu Myers and E. palu n.sp., but differs from both species in several ways. In E. steelei , the male gnathopod 2 basis bears a row of robust setae on the anterodistal margin (absent in E. lapu and E. palu ) and lacks the well-developed palmar shelf and the welldeveloped ridge which occurs on the inner face of the propodus of E. lapu and E. palu . In addition, the basis of pereopod 6 is more elongate and the posterior margin is concave. In addition, E. steelei differs from E. palu n.sp. in the long setae on the male coxa 1–2 and in the subquadrate epimeron 3 (two teeth in E. palu ).

This species can be distinguished from other Elasmopus species from Mauritius by the following combination of characters: the densely setose distal margin of coxae, the densely setose posterior margin of male gnathopods 1 and 2; the medially expanded dactylus of the male gnathopod 2, the striate sabre seta on the propodus of pereopods 3 and 4 and the characteristically shaped basis of pereopod 6.

Type locality. Souillac , Mauritius .

Distribution. Mauritius.

Etymology. This species is named after Prof. Donald H. Steele of Memorial University of Newfoundland, in recognition for having introduced one of the authors (CA) to the study of amphipods.

Key to the species of Elasmopus recorded from Mauritius 1 Uropod 3 rami subequal in length ................................................................................................. 2

Uropod 3 rami unequal, inner ramus shorter than outer ................................................................ 4 2 Telson entire ......................................................................................... ( Figs. 5, 6) E. pseudinteger

Telson cleft ..................................................................................................................................... 3

3 Telson with longest robust seta as long as telson; male G2,

propodus pyriform, posterior margin with medial tooth; dactylus broad, two-thirds length of propodus ................................................ ( Figs. 9, 10) E. souillacensis

Telson with longest robust seta less than a quarter length of telson; male G2 propodus subquadrangular posterior margin without medial tooth, dactylus relatively slender, half length of propodus .................................................................................................................... ( Fig. 12) E. spinimanus

4 Pereopods 3–4 propodus posterodistal margin with striate sabre shaped robust seta .......................................................................................................................... 5

Pereopods 3–4 propodus posterodistal margin with straight robust setae only ....................................................................................................................................... 8

5 Pereopods 3–7 dactylus posterior margin with small nipple-like projections ............................................................................................. ( Fig. 11) E. spinidactylus

Pereopods 3–7 dactylus without nipple-like projections ............................................................. 6

6 Gnathopod 2 male basis anterior margin with dense brush of long setae, propodus with two teeth on posterior margin ........................................ E. molokai pilosus

Gnathopod 2 male basis anterior margin without dense brush of long setae, propodus posterior margin lacking teeth .................................................................... 7

7 Epimeron 3, posterodistal margin without teeth, male coxae 1–2 with some setae as long as coxa ................................................................ ( Figs. 13, 14) E. steelei

Epimeron 3, posterodistal margin with two small teeth, male coxae 1–2 with setae much shorter than length of coxae ................................................. ( Fig. 3) E. palu

8 Pereopod 6–7, basis deeply castelloserrate ................................................ ( Fig. 4) E. pectenicrus

Pereopod 6–7, basis weakly serrated ............................................................................................. 9

9 Gnathopod 2, male propodus posterior margin densely setose .................. ( Figs. 1, 2) E. menurte

Gnathopod 2, male propodus posterior margin only weakly setiferous ...................................................................................................................................... 10

10 Coxa 1– 2 male with some long setae on distal margin .............................................................. 11

Coxa 1– 2 male with short setae only .......................................................................................... 12

11 Coxa 1 male anterodistal corner acute, P7 basis distinctly longer than broad .................................................................................... E. pseudaffinis form B Ledoyer

Coxa 1 male anterodistal corner obtuse P7 basis almost as broad as long ........................................................................................... E. pseudaffinis form A Ledoyer

12 Gnathopod 2 male dactylus two-thirds length of propodus, fitting, when in closed position, into pit on posterior margin of propodus ................. ( Figs. 7, 8) E. puteus

Gnathopod 2 male dactylus less than half length of propodus, lacking pit for reception of tip ....................................................... Elasmopus sp. Ledoyer (1978)

Biogeographic remarks

The genus Elasmopus is one of the most diverse amphipod genera on the shallow reefs of Mauritius. Thirteen species are now recorded from the island of which at least five species are currently thought to be endemic to Mauritius (or perhaps to the Mascarenes). Three species recorded by Ledoyer ( E. pseudaffinis form A, E. pseudaffinis form B and Elasmopus sp. ) may also prove to be endemics. Both age and isolation favour the development of endemics (Myers & Giller, 1988). The relatively high endemicity of Mauritius, not only for amphipods, but also for its terrestrial fauna, suggests a long evolutionary history. According to McDougall & Chamalaun (1969) volcanic rocks of Mauritius date only to the early Pliocene (7.8 my) but either Mauritius, a Mauritius progenitor, or other Masacarene islands must, in our opinion, be considerably older, facilitating anagenesis and phylogenesis probably since the late Cretaceous, as in the case of the Seychelles.

Of the Mauritius Elasmopus spp. , two species are currently thought to be cosmopolitan ( E. spinidactylus and E. pectenicrus ), and one species ( E. menurte ), previously known only from the Eastern Indian ocean, is now reported from the Western Indian Ocean.

Of the new species described herein, E. palu resembles E. lapu from Fiji; E. steelei also resembles E. lapu as well as E. ecuadorensis from the eastern Pacific; E. pseudinteger appears to be closely related to E. integer from the Society Islands; and E. puteus resembles E. gracilis a widespread Indo-Pacific species.

ACKNOWLEDGMENTS. We are grateful to the University of Mauritius and the Tertiary Education Commission for their support in carrying out the current study. The authors are deeply indebted to Prof. Indur Fagoonee of the University of Mauritius for his guidance and constant support in carrying the current research. Thanks also due to University of Mauritius (Higher Technical Education Plan) for fully sponsoring visits of one of us (C.A.) to University College Cork, Ireland. We thank Prof. J. Davenport and the staff of the Department of Zoology at University College Cork, for their hospitality and support.