Cochinorchestia metcalfeae, 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 : 164-169

Cochinorchestia metcalfeae sp. nov.

( Figs 7–10 )

Types. Holotype, male, 7 mm, MAGNT Cr018592, opposite Channel Island, Wickham Point, Darwin Harbour, Northern Territory, Australia (12°31.482'S 130°52.207'E), mangroves, hinterland margin, coll. K. Metcalfe, station LG16. Paratypes: 1 mature female, 9.1 mm, 2 males MAGNT Cr018593, same locality.

Type locality. Opposite Channel Island, Wickham Point, Darwin Harbour, Northern Territory, Australia (12°31.482'S 130°52.207'E).

Additional material. 1 male, MAGNT Cr018594, Charles Darwin National Park, Darwin Harbour, Northern Territory, Australia (12°27.25'S 130°52.19'E), mangrove tidal flat, K. Metcalfe, station E14.

Etymology. Named for Kristin Metcalfe who made important collections used in this study.

Habitat. Marsh-hoppers, mangrove tidal flat, within or on tree trunks in stilted mangrove ( Rhizophora stylosa ) dominated community.

Description. Based on holotype, male, 7 mm, MAGNT Cr018592.

Head with continuous row of long, slender scales on ventroproximal surface. Eye medium (1/5–1/3 head length). Antenna 2 shorter than head and first 3 pereonites; peduncular articles slender, article 5 longer than article 4; virgula divina present. 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 sexually dimorphic; subchelate; coxa 1 smaller than coxa 2; posterior margin of merus, carpus and propodus each with lobe covered in palmate setae, palmate lobes in both male and female; carpus longer than propodus, 1.6 × as long as propodus, 2.4 × as long as broad; propodus 'subtriangular' with well developed posterodistal lobe, anterior margin with 1 group of robust setae, posterolateral surface with 6 serrate setae, medial surface without cuspidate setae, posteromedial surface with 9 serrate setae, posterior margin without cuspidate setae, posterior margin without serrate setae, palm with 7 serrate setae, transverse, without spine patch on posterodistal corner; dactylus subequal in length to palm, simplidactylate, without anterodistal denticular patch. Gnathopod 2 sexually dimorphic; subchelate; basis slender; ischium without lobe on anterior margin, without anterodistal lobe on medial surface; carpus triangular, reduced (enclosed by merus and propodus), posterior lobe absent, not projecting between merus and propodus; propodus subovate, 1.8 × as long as wide; palm extremely acute, reaching about 55% along posterior margin, smooth, without protuberance or shelf near dactylar hinge, lined with robust setae (6 medial, 12 lateral), posteromedial surface of propodus with groove, with cuticular patch at corner of palm; dactylus subequal in length to palm, curved, without anteroproximal bump, posterior margin smooth, not modified distally, blunt. Pereopods 2–4 coxae wider than deep. Pereopods 3–7 dactyli without anterodistal denticular patch. Pereopod 4 carpus significantly shorter than carpus of pereopod 3. Pereopod 5 propodus distinctly longer than carpus. Pereopod 6 shorter than pereopod 7; coxa posterior lobe inner view posteroventral corner rounded, posterior margin perpendicular to ventral margin, posterior lobe without ridge, without marginal setae. Pereopod 7 basis lateral sulcus absent, posterior margin with broad, small serrations, each with a small seta, posterodistal lobe absent; distal articles (merus and carpus) slender; merus posterior margin straight, not expanded.

Pleon. Epimeron 3 posterior margin smooth without setae, posteroventral corner with small subacute tooth, ventral margin without robust setae. Uropod 1 peduncle with 8 robust setae, distolateral robust seta present, very large (1/3 – 1/2 length of outer ramus), with simple tip; inner ramus subequal in length to outer ramus, inner ramus with 4 marginal robust setae in 1 row; outer ramus with 3 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 with 2 marginal robust setae in 1 row. Uropod 3 peduncle with 1 robust seta; ramus not fused to peduncle, shorter than peduncle, as long as broad, triangular, with 2 apical setae. Telson as broad as long, apically incised, dorsal midline vestigial or absent, with 2 apical robust setae per lobe.

Female (sexually dimorphic characters). Based on female, 9.1 mm, MAGNT Cr018593. Gnathopod 1 subchelate; posterior margin of merus, carpus and propodus each with lobe covered in palmate setae; propodus anterior margin without groups of robust setae, palm with 4 distal serrate setae, strong concave, without spine patch on posterodistal corner. Gnathopod 2 mitten-shaped; basis slender; ischium without lobe on anterior margin; posterior margin of merus, carpus and propodus each with lobe covered in palmate setae; carpus well developed (not enclosed by merus and propodus), posterior lobe present, projecting between merus and propodus; palm obtuse, nearly straight; dactylus curved, posterior margin smooth. Oostegites long (length greater than 2 × width), longer than wide, weakly setose, about 12 setae with simple smooth tips.

Remarks. Gnathopod 2 of the smaller male has a narrow distal shelf (absent in adult) and fewer robust setae (2 medial, 5 lateral) along the palm. Cochinorchestia metcalfeae sp. nov. belongs to the small group of species ( C. metcalfeae , C. morini , C. sp. of Bussarawich 1985) with a smooth margin on the gnathopod 2 palm. The gnathopod 2 propodus of C. metcalfeae is long and subovate which separates it from the other two species.

Distribution. Australia. Darwin Harbour, Northern Territory (current study).

Figures

FIGURE 7. Cochinorchestia metcalfeae sp. nov., male, holotype, 7 mm, MAGNT Cr 018592; female, paratype, 9.1 mm, MAGNT Cr 018593; Wickham Point, Darwin Harbour, Northern Territory, Australia. Scale line for MX 1 IP represents 0.1 mm, remainder represent 0.2 mm.

FIGURE 8. Cochinorchestia metcalfeae sp. nov., male, holotype, 7 mm, MAGNT Cr 018592; female, paratype, 9.1 mm, MAGNT Cr 018593; Wickham Point, Darwin Harbour, Northern Territory, Australia. Scale line for female G 2 represents 0.2 mm, remainder represent 0.5 mm.

FIGURE 9. Cochinorchestia metcalfeae sp. nov., * male, holotype, 7 mm, MAGNT Cr 018592; male, paratype, MAGNT Cr 018593; Wickham Point, Darwin Harbour, Northern Territory, Australia. Scale lines for U 1 - 2 represent 0.2 mm, T, U 3 represent 0.1 mm, remainder represent 0.5 mm.

FIGURE 10. Cochinorchestia metcalfeae sp. nov., male, holotype, 7 mm, MAGNT Cr 018592; Wickham Point, Darwin Harbour, Northern Territory, Australia. Scale lines represent 0.5 mm.