Mallacoota magnimerus, Appadoo, Chandani & Myers, Alan A., 2006

Appadoo, Chandani & Myers, Alan A., 2006, Melitids (Crustacea: Amphipoda) of the genera Ceradocus and Mallacoota from Rodrigues Island (Indian Ocean), Zootaxa 1370, pp. 1-22 : 15-19

Mallacoota magnimerus sp. nov.

Figures 10–13

Type material. HOLOTYPE, Male, 4.8 mm, Grande Pate, Mathurin Bay, 19?° 39.307 ’S, 63 ° 24.950 ’E, Rodrigues, 29 September 2001, dead coral rock, 14–16 m, SCUBA, collectors N.L. Bruce & J. Smith, AM P 73607 .

PARATYPES. 1 male, 4.4 mm, AM P 73609 , 1 female, 4.8 mm, AM P 73608 , 3 males same data as holotype. 1 male, 1 female, AM P 73680 , Grande Pate, Mathurin Bay, 29 September 2001, loose coral rubble on hard bottom, 17 m, SCUBA, N.L. Bruce & Jonathan Smith.

Description. Male, 4.8 mm. Head with subocular notch. Eyes oval. Antenna 1 peduncle article 1 with few setae; subequal to article 2; article 3, 0.4 x as long as article 1; primary flagellum longer than peduncle with 20 articles; accessory flagellum with 2 - articulate. Antenna 2 peduncle article 5, 0.75 x article 4, with long slender setae; flagellum shorter than peduncle, 14 -articulate. Mandible palp article 3 subequal to article 1, 1.2 x length of article 2, with two terminal setae. Lower lip mandibular lobes acute; inner and outer plates setose; outer plate with two robust setae on lobes. Maxilla 1 inner plate with two plumose apical setae and few marginal setae; outer plate with five serrate robust setae; palp two-articulate. Maxilla 2 outer plates with terminal setae, inner plates with terminal and marginal setae. Maxilliped palp 4 -articulate, article 1 with few setae, articles 2 and 3 with slender setae on inner margin. Gnathopod 1 coxa 1.3 x as long as wide, postero-distal corner notched, distal margin with short setae; basis 2.2 x as long as wide, posterior margin with patches of long setae; carpus 1.9 x as long as wide, posterior margin with long setae; propodus slender 1.8 x as long as broad, palmar margin oblique and lined with short setae and a few long setae and a robust setae at postero-distal corner; dactylus slender and fitting length of palm. Gnathopod 2 coxa 1.4 x as long as broad, distal margin with short setae, postero-distal corner notched; basis slender, 4 x as long as broad; carpus triangular, 1.5 x as broad as long, anterior margin with few robust setae; propodus robust 1.6 x as long as broad, posterior margin with patches of long setae; palmar margin with 3 large protuberances, the first one weakly crenulate and lined with two robust setae and few patches of slender setae, the second one with one robust seta, the third one shallow and rounded, short slender setae present in indentations, palmar margin oblique; dactylus robust extending beyond length of palm, inner margin weakly crenulate. Pereopod 3 coxa 1.9 x as long as broad, postero-distal corner notched, distal margin with few setae; basis slender 4 x as long as broad; propodus 1.3 x length of carpus, posterior margin with short setae; dactylus slender. Pereopod 4 coxa 1.2 x as long as broad, postero-distal corner notched; basis 3.2 x as long as broad; propodus 1.4 x carpus; dactylus slender. Pereopod 5 coxa 1.4 x as broad as long, bilobed, posterior lobe longer than anterior lobe, basis as long as broad, anterior margin with few robust setae; merus anterior and posterior margin weakly extended ventrally with robust setae; propodus 1.8 x carpus, anterior margin with few robust setae; dactylus slender. Pereopod 6 coxa rectangular, basis 1.1 x as long as broad, anterior margin serrated with numerous robust setae, posterior margin with few short setae and distally expanded into a lobe; merus 1.7 x as broad as long, anterior margin with short robust setae and few patches of slender setae, posterior margin with long setae, antero-distal margin weakly produced, postero-distal margin expanded and produced and spanning beyond the length of the carpus; propodus 1.5 x length of carpus, 3.1 x as long as broad, anterior margin with robust setae, posterior margin with patches of slender setae, dactylus slender. Pereopod 7 coxa 1.1 x as long as broad, basis as long as broad, anterior margin with short robust setae, posterior margin weakly expanded with very short setae; merus 1.4 x as broad as long, anterior margin ventrally produced to about one quarter the length of carpus, and with patches of short robust setae, posterior margin expanded and produced into a lobe extending as long as the length of carpus, posterior margin with several patches of long slender setae; carpus 1.4 x as long as broad, narrow at the proximal end, and expanded at the distal end; propodus 1.5 x carpus, posterior margin with patches of long slender setae; dactylus elongate. Epimeron 3 postero-distal margin produced. Uropod 1 peduncle 1.1 x length of rami, outer margin with robust setae, rami subequal with robust setae on outer margin and at distal end. Uropod 2 peduncle 1.5 x as long as broad, with a triangular medial projection, and a robust seta on distal margin, outer ramus 0.9 x inner ramus, inner ramus outer margin lined with stout robust setae, both rami with three to four well-developed terminal robust setae. Uropod 3 peduncle 1.5 x as long as broad, 0.75 x length of outer ramus; outer ramus 1.1 x inner ramus, outer margin with four patches of robust setae, distal margin of both rami with three robust setae and a few long slender setae. Telson cleft to 75 % its length, with acute apices and two robust setae.

Female. Ovigerous, 4.8 mm. Gnathopod 1 coxa 2 x as long as broad, antero-distal margin notched, distal margin with few slender setae, basis 3.3 x as long as broad, carpus 1.8 x as long as broad, posterior margin with several patches of long, slender setae; propodus 0.9 x carpus, posterior margin with several patches of setae, medial diagonal row of setae, palm oblique, dactylus slender and fitting palm. Gnathopod 2, coxa 2.4 x as long as broad; basis 3.1 x as long as broad, posterior margin with one patch of long slender setae; carpus 2.2 x as long as broad, propodus elongate, 3.2 x as long as broad, anterior margin with three groups of short setae, posterior margin with several groups of long slender setae, palm oblique with short setae, one robust seta and a patch of slender setae at postero-distal corner. Pereopods 6 and 7 sexually dimorphic, with merus in both pereopods only weakly produced ventrally, other features similar to male.

Remarks. Mallacoota magnimerus sp. nov. has a distinctive large merus in pereopods 6 and 7. Two Mallacoota species show this feature, Mallacoota insignis (Chevreux) and M. subinsignis Ledoyer. In Mallacoota insignis , however the merus is not produced as far as the entire length of carpus and coxae 1–4 are not notched. The male gnathopod 2 palm is more transverse in M. magnimerus sp.nov. and the excavations are at more regular intervals, the palm is weakly setiferous as opposed to M. insignis which is densely setose. Also the telson has acute apices and two short robust setae in the new species while in M. insignis the telson has weakly developed apices with four long robust setae. Mallacoota magnimerus sp. nov. differs from M. subinsignis which possesses an inflated carpus in pereopod 6.

Distribution. Rodrigues

Etymology. Named from Latin ‘magnus’ = large, referring to the large merus of pereopods 6 and 7 in males of the species.

Figures

FIGURE 10. Mallacoota magnimerus sp. nov., male holotype, 4.8 mm, Grande Pate, AM P 73607, female paratype, 4.8 mm, Grande Pate, Mathurin Bay, AM P 73608. Scales: a = 1 mm (whole specimen), b = 0.5 mm (female G 1, female G 2, female P 7), c = 0.2 mm (enlargement of female G 2).

FIGURE 11. Mallacoota magnimerus sp. nov., male holotype, 4.8 mm, Grande Pate, Mathurin Bay, AM P 73607. Scale bar = 0.5 mm (P 3 – P 7).

FIGURE 12. Mallacoota magnimerus sp. nov., male holotype, 4.8 mm, Grande Pate, Mathurin Bay, AM P 73607; male paratype, 4.4 mm (MX 2, T), Grande Pate, Mathurin Bay, AM P 73609. Scales: a = 0.1 mm (MX 1, MX 2, LL, Md), b = 0.1 mm (U 1 – U 3), c = 0.05 mm (MXPp), d = 0.05 mm (T).

FIGURE 13. Mallacoota magnimerus sp. nov., male holotype, 4.8 mm, Grand Pate, Mathurin Bay, AM P 73607. Scales: a = 0.5 mm (A 1, G 2), b = 0.2 mm (A 2, enlargement of G 2), c = 0.2 mm (G 1).