Mallacoota latibrachium (Walker), 1982

Appadoo, Chandani, Myers, Alan A. & Fagoonee, Indur, 2002, The genus Mallacoota (Crustacea, Amphipoda, Melitidae) from Mauritius, with description of a new species, Journal of Natural History 36 (7), pp. 767-796 : 782-787

Mallacoota latibrachium (Walker)

(®gures 10±12)

Elasmopus latibrachium Walker, 1905: 928 , pl. 88 (6±10).

? Elasmopus odontopla x: Pirlot, 1936: 326, ®gure 146.

Maera latibrachium: Sivaprakasam, 1970: 41 , ®gure 3.

Maera latibranchium (sic): Ledoyer, 1967: 129, ®gure 10.

Mallacoota latibrachium: Ledoyer, 1982: 556 , ®gure 211.

Material examined

3, 3 from Padina sp. , La Cuvette, 14 May 1998. 1, two juv. from mixture of Digenia simplex , Laurencia papillosa , Centroceras clavulatum , Jania adherens and Padina, Roches Noire , 9 April 1999. 2 from Sargassum sp. and Ulva reticulata, La Cuvette , 5 May 1999. 1 from mixture of Padina , Sargassum densifolium , Pocockiella variegata, Bain Boeuf , 13 December 1999. 2, 2, ®ve juv. from mixture of Padina sp. , Turbinaria ornata (Turner) J. Agardh , Sargassum densifolium , Caulerpa sertulariodes , Digenia simplex , Pocockiella variegata and coral rubble, Bain Boeuf, 24 January 2000.

Description

Male. Length, 4.3 mm. Head with notch below cephalic lobe; eyes oval in shape with well-developed ommatidial disc. Antenna 1 twice as long as antenna 2; article 1 with robust setae on posterior margin; article 2 subequal to 1; article 3, 0.3 times article 2; primary ¯agellum 16-articulate and subequal to peduncle; articles 2, 3 and ¯agellum sparsely setose. Antenna 2, peduncle longer than ¯agellum; ¯agellum sevenarticulate. Mandible with a three-articulate palp; article 2 subequal to 1; article 3, 1.5 times article 2 and bearing two terminal and one medial setae. Maxilla 1 inner lobe with two plumose setae and marginal setae. Outer lobe with ®ve serrate robust setae, palp two-articulate. Maxilla 2 inner and outer plates with distal setae; inner plates with some setae extending to the marginal border. Maxilliped, inner plate with ®ne terminal setae, outer plates with stout apical and inner marginal setae; palp four-articulate, article 2 setose on inner margin, article 3 setose on distal margin. Lower lip mandibular lobes more rounded than acute, inner and outer lobes each have two blunt robust setae. Gnathopod 1 coxa 1.3 times as long as wide; notch with seta present, ventral margin with very small setae; carpus posterior margin densely setose with two medial groups of setae; propodus 1.2 times carpus, palm de®ned by stout robust setae, palmar margin with small robust setae and ®ne setae; dactylus slender and ®tting palm. Gnathopod 2 stouter and more robust than gnathopod 1; coxa notched, 1.6 times as long as wide, notch with a small seta; basis 1.8 times as long as wide, with a patch of setae on posterior margin, distal end of basis irregularly lobulated; ischium bearing a carina on dorsal margin; carpus 1.2 times as long as broad; propodus ventral margin with few patches of setae, palm oblique, palmar margin bearing six stout robust setae; dactylus curved. Pereopod 3 coxa notched, 1.8 times as long as wide, notch with seta; basis with robust setae on anterior margin and setae on posterior margin; merus widening distally and anterior margin with three robust setae; carpus subequal to merus; propodus 1.2 times length of carpus, posterior margin spinous. Pereopod 4 coxa 1.8 times as long as wide, posterior margin excavate; propodus 1.3 times carpus; other features similar to pereopod 3. Pereopod 5 coxa bilobed, 1.4 times as wide as long; basis subovate, 1.4 times as long as wide, anterior margin spinous, posterior margin with ®ne setae.

Pereopod 6 basis subquadrate, distal margin with short setae and weakly serrated, anterior margin with strong robust setae; carpus 2.1 times as long as wide; propodus 1.8 times carpus, six times as long as wide. Pereopod 7 coxa lobular, 1.4 times as long as wide; basis anterior margin spinous, posterior margin weakly crenulate with short robust setae; carpus 1.9 times as long as wide; propodus 1.6 times length of carpus, four times as long as wide.

Epimeron 3 distally produced into a cusp, no robust setae visible. Uropod 1 peduncle 1.3 times outer ramus; outer and inner rami equal. Uropod 2 peduncle 1.2 times length of outer ramus; rami subequal. Uropod 3 peduncle 1.6 times as long as wide; rami 1.2 times peduncle. Telson cleft to three-quarter its length with very acute apices with three robust setae.

Female. Length, 3.6 mm (mature, with eggs). Female antennae and epimeron 3 similar to male. Gnathopod 1 coxa notched, 1.8 times as long as wide; basis three times as long as wide; carpus twice as long as wide; carpus and propodus subequal. Gnathopod 2 coxa 1.8 times as long as wide; basis three times as long as wide; carpus 0.6 times as wide as long; propodus 1.8 times as long as wide, palm oblique bearing ®ne setae and robust setae; dactylus short and reaching de®ning cusp. Uropods similar to male. Telson in the female apices notched, but not as acute as in males.

Remarks

Mallacoota latibrachium males range from 3.3 to 5.4 mm while females range from 3.5 to 4.3 mm in size in the current collection. Present material agrees with the description of Ledoyer (1982). The lack of setae and the strong robust setae on the peduncle segment 1 of antenna 1 distinguish this species from M. caerulea and M. schellenbergi . The species is distinguished from other Mallacoota spp. of Mauritius by the presence of a notch on coxae 1±3, by gnathopod 2 of males, with basis 1.8 times as long as wide, by epimeron 3 distally produced into a cusp and ventral margins without robust setae, and by the telson cleft to three-quarter its length and with acute apices.

Mallacoota latibrachium is recorded for the ®rst time from Mauritius. The species also shows a fairly wide distribution in the Indo-Paci®c as it has been recorded from several regions.

Habitat. Mallacoota latibrachium occurs in the intertidal zone to shallowsubtidal zones at depths less than 1 m, from three sites, La Cuvette, Bain Boeuf and Roches Noire. This species was found to be mostly associated with brown algae, for example, Padina sp. , Pocockiella variegata or Sargassum sp. , Mallacoota latibrachium appears to be more rare than other species of Mallacoota among the intertidal algae.

Type locality. Maldive and Laccadive archipelagoes .

Distribution. Madagascar, Mauritius, India, Maldive and Laccadive archipelagoes, Indonesia.