Microrchestia ntensis, Lowry, J. K. & Springthorpe, R. T., 2015

Lowry, J. K. & Springthorpe, R. T., 2015, Coastal Talitridae (Amphipoda: Talitroidea) from north-western Australia to Darwin with a revision of the genus Cochinorchestia Lowry & Peart, 2010, Zootaxa 3985 (2), pp. 151-202 : 180-185

Microrchestia ntensis sp. nov.

( Figs 19–21 )

Types. Holotype, male, 5.6 mm, MAGNT Cr013910, Port Keats, Northern Territory, Australia (14º06'S 129º33'E), low water spring tide, coll. K. Metcalfe.

Type locality. Port Keats, Northern Territory, Australia (14º06'S 129º33'E). Habitat. Marsh-hopper, semi-aquatic in salt marshes and mangrove swamps. Etymology. Named for the locality, Northern Territory.

Description. Based on holotype, male, 5.6 mm, MAGNT Cr013910.

Head slender scales on ventroproximal surface unknown. Antenna 1 reaching end or slightly beyond end antenna 2 peduncle. Antenna 2 less than half body length; peduncular articles slender, article 5 longer than article 4, final flagellar article large, cone-shaped, forming virgula divina. Upper lip without robust setae. Mandible left lacinia mobilis 4-cuspidate. Maxilla 1 with small palp, 1-articulate. Maxilliped palp article 2 distomedial lobe well developed; article 4 small, well defined.

Pereon. Gnathopod 1 subchelate; smaller than coxa 2; posterior margin of merus, carpus and propodus each with lobe covered in palmate setae; carpus longer than propodus, 1.2 × as long as propodus, 1.75 × as long as broad; propodus subrectangular, anterior margin with 2 groups of robust setae, posteromedial surface with 3 serrate setae; palm transverse with about 7 serrate setae, without spine patch on posterodistal corner; dactylus subequal in length to palm, simplidactylate, without anterodistal denticular patch. Gnathopod 2 sexually dimorphic; subchelate; basis slightly expanded; ischium without lobe on anterior margin, without anterodistal lobe on medial surface; posterior margin of merus, carpus and propodus each without lobe covered in palmate setae; carpus triangular, reduced (enclosed by merus and propodus), posterior lobe absent, not projecting between merus and propodus; propodus subtriangular, 1.6 × as long as wide; palm acute, reaching about 55% along posterior margin, palm weakly toothed, sinuous, with broad distal shelf, shallow sinus, broad cuticular rise, rounded tooth, lined with robust setae, with small mid to proximopalmar sinus, posterodistal corner with socket, posteromedial surface without groove, with cuticular patch at corner of palm; dactylus subequal in length to palm, broadly curved, without anteroproximal bump, posterior margin smooth, not modified distally, blunt; gill simple. Pereopods 2–4 coxae wider than deep. Pereopods 3–7 simplidactylate; dactyli without anterodistal denticular patch. Pereopod 3 dactylus with small cuticular dome on posterior margin at juncture with unguis. Pereopod 4 subequal or slightly shorter than pereopod 3; carpus significantly shorter than carpus of pereopod 3; dactylus similar to pereopod 3 dactylus, not thickened proximally or notched, with small cuticular dome on posterior margin at juncture with unguis. Pereopod 5 propodus distinctly longer than carpus; dactylus without anterodistal denticular patch. Pereopods 6–7, long (1/2 length of body). Pereopod 6 not sexually dimorphic, shorter than pereopod 7; coxa posterior lobe inner view posteroventral corner rounded, posterior margin oblique to ventral margin, posterior lobe without ridge, posterior lobe without marginal setae; coxal gill lobate, anterior and posterior margins smooth, subapically incised along posterior margin. Pereopod 7 merus and carpus slightly incrassate; basis lateral sulcus absent, posterior margin with broad, small serrations, each with a small seta, posterodistal lobe present, small, shallow, narrowly rounded; merus posterior margin expanded distally, subtriangular; carpus subrectangular.

Pleon. Pleopods all well developed, biramous. Epimeron 2 slightly longer than epimeron 3. Epimeron 3 posterior margin smooth, without setae, posteroventral corner with small subacute tooth, ventral margin without robust setae. Uropod 1 peduncle with 4 robust setae, distolateral robust seta present, very large (1/3 length of outer ramus), with simple tip; inner ramus subequal in length to outer ramus, with 1 row of 3 marginal robust setae; outer ramus without marginal robust setae. Uropod 2 peduncle with 4 robust setae; inner ramus subequal in length to outer ramus, with 2 marginal robust setae; outer ramus without marginal robust setae. Uropod 3 peduncle with 2 robust setae; ramus not fused to peduncle, ramus shorter than peduncle, about 2 × as long as broad, linear (tapering distally), with 3 apical setae. Telson slightly longer than broad, apically incised, dorsal midline about halfway, with 2 apical robust setae per lobe.

Female. Unknown.

Remarks. Microrchestia ntensis sp. nov. is distinguished from other species of Microrchestia by the cuticular domes on the posterior margins of the dactyli of pereopods 3–4. It is similar to M. watsonae Lowry & Peart, 2010 from Lizard Island, Great Barrier Reef. Microrchestia ntensis is a small species, half the size of M. watsonae ; the gnathopod 1 carpus is slightly longer than the propodus (1.6 × in M. watsonae ); the propodus length is 1.75 × breadth (2.3 × in M. watsonae ) and the gnathopod 2 palm reaches about 55% (48% in M. watsonae ), the basis of pereopod 6 has a more rounded posterior margin with a sloping posteroproximal corner (straight with a rounded corner in M. watsonae ) and the basis of pereopod 7 is more rounded and less serrate than that of M. watsonae .

Distribution. Australia. Port Keats, Northern Territory (this study).

Figures

FIGURE 19. Microrchestia ntensis sp. nov., male, holotype, 5.6 mm, MAGNT Cr 013910, Port Keats, Northern Territory, Australia. Scale lines represent 0.1 mm.

FIGURE 20. Microrchestia ntensis sp. nov., male, holotype, 5.6 mm, MAGNT Cr 013910, Port Keats, Northern Territory, Australia. Scale lines for UR, G 2 represent 0.5 mm, EP 1 - 3, G 1 represent 0.2 mm, remainder represent 0.1 mm.

FIGURE 21. Microrchestia ntensis sp. nov., male, holotype, 5.6 mm, MAGNT Cr 013910, Port Keats, Northern Territory, Australia. Scale lines represent 0.2 mm.