Tropicorchestia derbyensis, 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 : 191-193

Tropicorchestia derbyensis sp. nov.

( Figs 26–29 )

Type material. Holotype, male, 11.0 mm, AM P.97470, mangroves near the Derby Jetty, Derby, Western Australia (17°17.732'S 123°36.431'E), 20 May 2010, J.K. Lowry. Paratype, female, AM P. 97843, same locality.

Type locality. Mangroves near the Derby Jetty, Derby, Western Australia (17°17.732'S 123°36.431'E).

Etymology. Named for the type locality, Derby, Western Australia.

Habitat. Marsh-hoppers living on muddy substrate under leaves near outer margin of mangroves.

Description. Based on holotype, male, 11.0 mm, AM P.97470.

Head slender scales on ventroproximal surface unknown. Antenna 1 short, slightly longer than article 4 of antenna 2 peduncle. Antenna 2 slightly less than half body length; article 5 longer than article 4, peduncular articles with sparse large robust setae, final flagellar article large, cone-shaped, forming virgula divina. Mandible left lacinia mobilis 4-cuspidate. Maxilla 1 with small palp, 2-articulate. Lower lip with vestigial inner plates. Maxilliped palp article 2 distomedial lobe well developed; article 4 reduced, button-shaped.

Pereon. Gnathopod 1 subchelate; coxa smaller than coxa 2; carpus longer than propodus, 1.7 × as long as propodus, 2.8 × as long as broad; propodus 'subtriangular' with well developed posterodistal lobe, anterior margin with 3 groups of robust setae, medial surface with 15 cuspidate setae, posterior margin with 3 cuspidate setae; palm with 7 serrate setae, transverse, without spine patch on posterodistal corner; dactylus subequal in length to palm, cuspidactylate (vestigial), without anterodistal denticular patch. Gnathopod 2 sexually dimorphic; subchelate; basis slightly expanded; ischium with rounded lobe on mid-anterior margin, with distal triangular anterodistal lobe on medial surface; carpus triangular, reduced (enclosed by merus and propodus), posterior lobe absent, not projecting between merus and propodus; propodus subovate, 1.6 × as long as wide, palm acute, reaching about 31% along posterior margin, smooth, evenly rounded, lined with robust setae (5 large, 14 small lateral and 5 large, 13 small medial), posteromedial surface of propodus with groove, with cuticular patch at corner of palm; dactylus longer than palm, curved, without anteroproximal bump, posterior margin with minute cuticular surface, attenuated distally. Pereopods 2–4 coxae as wide as deep (2–3) or wider than deep (4). Pereopods 3–7 dactyli without anterodistal denticular patch. Pereopod 4 subequal to pereopod 3; carpus similar in length to pereopod 3 carpus; dactylus thickened proximally with a slight notch midway along posterior margin. Pereopod 5 propodus distinctly longer than carpus. Pereopods 6–7 not sexually dimorphic, longer than pereopods 3–5. Pereopod 6 coxa posterior lobe inner view posteroventral corner rounded, posterior margin perpendicular to ventral margin, posterior lobe without ridge. Pereopod 7 basis lateral sulcus absent, posterior margin with distinct minute serrations, each with a small seta, posterodistal lobe shallow, narrowly rounded; distal articles (merus and carpus) slender; propodus setation without large distal tuft of setae.

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. Uropod 1 peduncle with 8 robust setae, distolateral robust seta present, large (1/4 length of outer ramus), with simple tip; inner ramus subequal in length to outer ramus, with 4 marginal robust setae in 1 row. Uropod 2 peduncle with 3 robust setae; inner ramus subequal in length to outer ramus, with 2 marginal robust setae; outer ramus with 3 marginal robust setae in 1 row. Uropod 3 peduncle with 1 robust seta; ramus not fused to peduncle, shorter than peduncle, 2.5 × as long as broad, linear (tapering distally), with 1 marginal and 3 apical setae. Telson longer than broad, apically incised, dorsal midline entire, with 5 marginal and apical robust setae per lobe (2 lateral and 3 apical).

Female (sexually dimorphic characters). Based on female, AM P.97843. Gnathopod 1 parachelate; posterior margin of merus, carpus and propodus each without lobe covered in palmate setae; propodus subrectangular anterior margin with 3 groups of robust setae. Gnathopod 2 mitten-shaped; basis slightly expanded; ischium without lobe on anterior margin; posterior margin of merus, carpus and propodus each with lobe covered in Remarks. Tropicorchestia derbyensis sp. nov. differs from T. glasbyi sp. nov., the only other species in the genus, mainly in the longer propodus of gnathopod 1 (1.7 × in T. derbyensis , 1.4 × in T. glasbyi ); uropod 3 peduncle with one robust seta (2 in T. glasbyi ), ramus longer (2. 5 × longer than broad in T. derbyensis , 1.4 × in T. glasbyi ) with one marginal seta in T. derbyensis (absent in T. glasbyi ).

Distribution. Australia. Derby, Western Australia (this study).

Figures

FIGURE 26. Tropicorchestia derbyensis sp. nov., male, holotype, 11.0 mm, AM P. 97470, near Derby Jetty, Derby, Western Australia. Scale line for A 2 represents 0.2 mm, remainder represent 0.1 mm.

FIGURE 27. Tropicorchestia derbyensis sp. nov., male, holotype, 11.0 mm, AM P. 97470, near Derby Jetty, Derby, Western Australia. Scale line for U 3 represents 0.1 mm, CT represents 0.01 mm, remainder represent 0.2 mm.

FIGURE 28. Tropicorchestia derbyensis sp. nov., male, holotype, 11.0 mm, AM P. 97470; female, paratype, AM P. 97843; near Derby Jetty, Derby, Western Australia. Scale lines represent 0.2 mm.

FIGURE 29. Tropicorchestia derbyensis sp. nov., male, holotype, 11.0 mm, AM P. 97470, near Derby Jetty, Derby, Western Australia. Scale lines represent 0.5 mm.