Melita corticis, Appadoo & Myers, 2005

Appadoo, C & Myers, AA, 2005, Amphipods of the Genera Ceradocus, Dulichiella, Melita and Nuuanu (Crustacea: Melitidae) from Mauritius, Indian Ocean, Records of the Australian Museum 57, pp. 221-236 : 227-230

Melita corticis n.sp.

Figs. 5–6

Melita zeylanica Appadoo & Steele, 1998: 639 .

Type material. HOLOTYPE 3, 4.3 mm, AM P60867, 0–1 m depth, living on a mixture of Ulva lactuca and Ulva reticulata, le Bouchon (20°28'S 57°40.5'E), C. Appadoo, 27 October 1998. PARATYPES: 13, 3♀♀, AM P60868, same data as holotype; 233, 16♀♀, and 10 juv. from Ulva lactuca and Ulva reticulata, Le Bouchon , 16 May 1998; 233, 2♀♀, 3 juv. from Ulva lactuca and Ulva reticulata, Le Bouchon , 27 October 1998.

Description. Male length, 6.2 mm. Head with subocular notch, eyes round, a ring of clear ommatidia surrounding a dark central core. Antenna 1 weakly setiferous, article 2, 1.3× article 1, article 3, 0.5× article 1; accessory flagellum 3-articulate; primary flagellum 16-articulate (possibly regenerating in this specimen), flagellum can be 27- articulate (observed from additional material). Antenna 2 weakly setiferous, peduncular article 5 subequal to 4, flagellum 8-articulate. Mandible palp article 3 slightly longer than 2, article 1, 0.3× article 3; article 2 with two groups of setae on posterior margin, article 3 with a few lateral and terminal setae. Maxilla 1 inner plate with 8 plumose apical setae; Lower lip with rounded mandibular lobes. Gnathopod 1 coxa 1.4× as long as broad with short setae on ventral margin; basis 3× as long as broad with a strong patch of setae on anterodistal margin; carpus 1.5× length of propodus; propodus with transverse palm and forming a hood above dactylus; dactylus with medial protrusion on posterior margin. Gnathopod 2 coxa subrectangular 1.5× as long as broad, with setae on distal margin; basis 2.9× as long as broad, with a few groups of long setae on anterior margin; merus slightly produced ventrodistally; carpus 1.2× as broad as long; propodus subrectangular, 1.6× as long as broad, palmar margin weakly convex, palm rounded, with short stout setae and slender setae; dactylus broad throughout its length and slightly tapered at tip and closing across inner face of propodus. Pereopod 3 coxa subrectangular, 1.6× as long as broad, with very short setae on ventral margin; propodus and carpus subequal; dactylus with distal unguis. Pereopod 4 coxa deeply excavate posteriorly; other features similar to pereopod 3. Pereopod 5 coxa about 1.2× as long as broad, anterior margin with robust setae, posterior margin weakly serrated with short setae; dactylus short and robust with terminal unguis. Pereopod 6 coxa lobular; basis subovate, 1.4× as long as broad, anterior margin with stout setae, posterior margin serrated with stout setae; propodus 2× length of carpus; other features similar to pereopod 5. Pereopod 7 basis, 1.3× as long as broad, anterior margin with numerous robust setae, posterior margin more convex and weakly serrated; other features similar to pereopod 6. Epimera 2 and 3 posterior margin weakly serrated, distal margins with a few stout setae. Urosomite 1 smooth. Urosomite 2 with two stout robust setae on each side. Uropods 1–2, rami subequal to each other and shorter than peduncle. Uropod 3 inner ramus rudimentary, with one robust seta; outer ramus 1-articulate, spatulate, 2.5× the length of peduncle, with robust setae and slender setae. Telson cleft to base, lobes with pointed apex; each lobe with two robust setae on distal inner margins and one on the outer margin; 1 or 2 robust setae present about half-way along inner margin.

Female: length, 3.3 mm (mature with eggs). Gnathopod 1 coxa subrectangular, 1.6× as long as broad; basis about three times as long as broad; carpus 1.3× length of propodus; propodus palm transverse, palmar margin with short setae; dactylus large at base and tapered at tip. Gnathopod 2, coxa 2× as long as broad; propodus subrectangular, 1.3× length of carpus with stout setae and slender setae on palm. Pereopod 6, coxa with a large hook-like anterior lobe.

Remarks. The present material falls into the group of Melita that lacks a second article on the outer ramus of uropod 3 (see Ledoyer, 1982: 568). It resembles M. pahuwai Barnard (1970) from Hawaii in having only one robust seta instead of 3 in the inner face of male gnathopod 1 propodus; in having the robust setae on the palmar margin of the female gnathopod 2 shorter than the inner facial robust setae rather than vice-versa and in lacking robust setae on the proximal outer margins of the telson.

It appears to be particularly closely related to Melita zeylanica Stebbing, 1904 , M. zeylanica kauerti J.L. Barnard 1972 and M. setiflagella Yamato 1988.

It can be distinguished from M. setiflagella Yamato (1988) by the well-developed circular eyes (smaller, slightly reniform eyes in M. setiflagella) by antenna 2 peduncular articles 5 and 4 being subequal (peduncular article 5 shorter than 4 in M. setiflagella) by antenna 2 being poorly setiferous and 8-articulate (densely setiferous and 15- articulate in M. setiflagella), and by female coxa 6 being without scale-like denticles.

It differs from Melita zeylanica Stebbing (1904) in the presence of an anterodistal bulge near the base of the dactylus in the male gnathopod, in the non-compressed carpus of the gnathopod 2 in females, and in the presence of a robust basofacial seta on the peduncle of uropod 1, the latter feature, however, may have been overlooked by Stebbing (1904). Unlike Melita zeylanica kauerti Barnard (1972: 235 , fig. 139–140) it has 2 (rather than 3) dorsolateral robust setae on urosomite 2 and one (rather than four) robust seta in the apex of the inner ramus of uropod 3. Barnard (1972) notes that Sri Lankan material of Melita zeylanica has one robust seta on uropod 3 inner ramus as in present material.

These four species form a group of related forms. The current material compares most closely with Melita zeylanica kauerti but that species is closer to M. setiflagella than it is to the present material. Also Melita zeylanica kauerti differs more from Melita zeylanica than it does from the present material. This material is considered to represent a new species that can be distinguished from its close congeners by the combination of characters shown in Table 1.

Habitat. Known only from Le Bouchon at depths of less than 1 m. The site is characterized by low salinity, greenalgal growth and some estuarine conditions, which is in agreement with the general occurrence of the genus in brackish waters ( Bousfield, 1973).

Type locality. Le Bouchon, Mauritius .

Distribution. Mauritius.

Etymology. From the Latin cortex meaning a cork, in reference to the name of the type locality.