Cymadusa microphthalma (Chevreux)

Appadoo, C & Myers, A. A., 2004, Corophiidea (Crustacea: Amphipoda) from Mauritius, Records of the Australian Museum 56 (3), pp. 331-362 : 344-345

Cymadusa microphthalma (Chevreux)

Grubia microphthalma Chevreux, 1901: 422 , figs. 46–49. Cymadusa microphthalma .—Appadoo & Steele, 1998: 639.

Material examined. 333, 3♀♀, 2 juv., AM P60636, from Digenia simplex , Dictyota divaricata and Gracilaria salicornia, Roches Noires (20°6.2'S 57°44.5'E), 9 April 1999; 633, 12♀♀, 16 juv., AM P60637, from Digenia simplex , Padina sp. and Jania adherens, Roches Noires , 6 August 1999; 13, 3♀♀, 3 juv., AM P60638, from Sargassum sp. , Amansia glomerata and Digenia simplex, Souillac (20°31'S 57°30.7'E), 14 October 1999; 13, 6♀♀, 8 juv., AM P60639, from Padina sp. and Digenia simplex, Roches Noires , 24 January 2000.

Diagnosis. Antenna 1 accessory flagellum 2-articulate, article 2 rudimentary. Coxae 1–4 distal margin with very short setae. Gnathopod 1 propodus palm oblique. Gnathopod 2 carpus subtriangular; propodus 2.5× length of carpus, palm with a small excavation near base of dactylus followed by a subrectangular process and a straight margin, palm with short slender setae; dactylus robust, medially expanded. Telson distally truncate.

A full description is given for this species as there is some confusion about synonymies of the species in literature, see remarks.

Description. Male, 9 mm. Head about as long as deep, distoventral margin excavate; eyes large with welldeveloped pale yellow ommatidia (in alcohol). Antenna 1 peduncle article 2, subequal with article 1; article 3, 0.25× article 1; accessory flagellum 2-articulate, article 2 rudimentary; primary flagellum 41-articulate. Antenna 2 poorly setiferous, peduncle article 5, 0.9× article 4; flagellum 23-articulate. Mandible palp well developed, article 3, 2.1×article 1, with apico-medial setae. Lower lip outer lobe broad, moderately notched, without robust setae; mandibular lobe rounded. Maxilla 1 inner plate subovate with few medial slender setae. Maxilla 2 inner plate narrow. Maxilliped palp article 3 slightly expanded distally; article 4 slender, conical and terminating in a nail. Gnathopod 1 coxa subovate, about as long as broad, anterodistally moderately expanded, distal margin with very short setae; basis 2.5× as long as broad, anterodistal lobe weak; carpus elongate, 1.8× as long as broad; propodus subequal to carpus, 1.8× as long as broad, palm oblique with 1 robust seta at posterodistal margin; dactylus fitting palm. inner margin toothed. Gnathopod 2 coxa subrectangular, 1.3× as long as broad, distal margin with minute setae; basis with small rounded anterodistal lobe, 2.3× as long as broad; carpus subtriangular, 0.8× as long as broad; propodus 2.5× length of carpus, palm with a small excavation near base of dactylus followed by a subrectangular process and a straight margin, palm with short slender setae; dactylus robust, medially expanded, inner margin teeth poorly defined. Pereopods 3–4, coxa subrectangular, 1.4× s long as broad, posterodistal margin with 1 group of slender setae; basis weakly expanded, 2.8× as long as broad; merus 1.8× as long as broad, anterior margin weakly expanded; carpus elongate, 2.3× as long as broad, 0.8× length of merus; propodus subequal to carpus, with groups of slender setae on posterior margin. Pereopod 5 coxa with moderate posterior lobe; basis expanded, length subequal with breadth; carpus 0.9× merus; propodus 1.4× carpus, posterior margin with slender and straight robust setae. Pereopod 6 basis subrectangular 1.5× as long as broad, anterior and posterior margins with a few robust setae; merus elongate, 2.4× as long as broad; carpus 2.6× as long as broad, 0.9× length of merus; propodus slender, 5× as long as broad, 1.4× length of carpus, posterior margin with groups of slender setae, anterior margin with slender setae and straight robust setae. Pereopod 7 similar to pereopod 6 but basis 1.6× as long as broad. Epimera 1–3 posterodistal margin rounded. Uropod 1 peduncle 2.8× as long as broad, outer margin with short fine setae, inner margin lined with robust setae, distal margin produced into an acute interramal process; outer ramus 0.8× inner ramus, both rami with numerous robust setae. Uropod 2 peduncle 2.8× as long as broad, distal margin with a small triangular interramal process; outer ramus 0.9× inner ramus, both rami with numerous robust setae. Uropod 3 peduncle 1.8× as long as broad, distal margin with robust setae; inner ramus with slender and robust setae at apex, outer ramus with a group of medial slender setae and 1 robust seta, two recurved apical robust setae. Telson distally truncate, with two groups of medial long slender setae.

Female, 10.3 mm (ovigerous). Gnathopod 1 coxa 1.3× as long as broad, anterodistal margin strongly produced, rounded, posterodistal margin with one group of slender setae, setae 0.3× length of coxa; basis 2.7× as long as broad, anterodistal lobe weak; carpus elongate, 1.6× as long as broad; propodus 1.2× length of carpus, 2× as long as broad, palm oblique with groups of slender setae and 1 robust seta at posterodistal margin; dactylus inner margin toothed. Gnathopod 2 coxa 1.5× as long as broad, posterodistal margin with 1 group of slender setae, setae 0.2× length of coxa; basis 2.6× as long as broad, anterodistal lobe weak; carpus cup-shaped, 0.9× as long as broad; propodus 1.7× length of carpus, palm oblique, weakly excavate with groups of slender setae, posterodistal corner with 1 robust seta; dactylus inner margin toothed.

Variation.Young males (5–6 mm): in gnathopod 2 the distal margin of the coxa has a group of slender setae, the propodus palm is barely excavate with fine slender setae and 1 robust seta on the inner face and the inner margin of the dactylus is strongly toothed.Young males (7.8 mm): the posterodistal corner of the coxa has fewer setae, the propodus lacks robust setae on the inner face, the palm is weakly crenate and the dactylus is strongly toothed.

Type locality. Seychelles .

Distribution. Seychelles, Mauritius.

Habitat. This species lives mostly amongst the brown algae, Sargassum sp. and Padina sp. , and red algae. It was collected at depths of less than 1 m from several sites on the north, east and south coasts. It was common at Roches Noires on the east coast and Bain Boeuf on the north coast.

Remarks. This species resembles the species described by Ledoyer (1982) from Madagascar under the name Cymadusa filosa form “B”. It differs from that species, however, in the male gnathopod 2 propodus palm, which is sinuous in present material but evenly convex in Ledoyer’s species and in the dactylus, which is medially expanded and short, fitting the palm, in the present material, but elongate, slender and strongly overlapping the palm in Ledoyer’s species. A comparison of the present material with Grubia microphthalma Chevreux (1901) is hampered by the fact that only a female was available to that author for the original description. Since the present material agrees well with the description of G. microphthalma , in all except secondary sexual male characters and since the type locality for this species is the Seychelles it seems reasonable, at least for the moment, to assign the present material to Cymadusa microphthalma (Chevreux) .

It is doubtful whether the species described under the name Cymadusa microphthalma by Sivaprakasam (1970a: 573, fig. 12) belongs in this species.

Cymadusa microphthalma is distinguished from all other Cymadusa from Mauritius except C. cavimana , by having only one patch of setae on the distal margin of coxae 1–4. It can be distinguished from C. cavimana by the shape of the propodus of the hyperadult male gnathopod 2, which has a small process and by the length of the dactylus which reaches the end of the palmar margin.