Platorchestia ano, Lowry, J. K. & Bopiah, Arundathi, 2013

Lowry, J. K. & Bopiah, Arundathi, 2013, The talitrid amphipods of Tonga (Crustacea, Amphipoda, Talitridae), Zootaxa 3681 (4), pp. 347-370 : 348-353

Platorchestia ano sp. nov.

( Figs 1–4 )

Platorchestia platensis .— Myers, 1985: 134, figs 108, 109.

Type material. Holotype male, 9 mm, AM P.87313, from white sand beach with thick cover of fine Zostera and other plant debris (about 5–6 cm deep) at top of intertidal, Ano Beach, Pangaimotu Island, Vava’u, Tonga (18°42’08.60”S 173°59’19.62”W), talitrids very abundant, J.K. Lowry & G.C.B. Poore, 11 October 2011; paratypes: 1 female, AM P.87314, 29 males, 149 females and juveniles (many juveniles, only 2 ovigerous females) AM P.87325, same locality as holotype.

Additional material examined. Five males (only 1 mature), 95 females and juveniles (many juveniles) AM P.87326, coarse coral rubble on top of fine white sand beach near the commercial harbour, Nuku’alofa, Tongatapu, Tonga (21°08.443’S 175°10.426’W), talitrids under dried algae on sand under coarse rubble, J.K. Lowry & G.C.B. Poore, 13 October 2011; 1 specimen, AM P.80738, Ano Beach, Pangaimotu Island, Vava’u, Tonga (18°42’S 173°59’W), Greg Towner, 19 September 2009.

Type locality. Ano Beach, Pangaimotu Island, Vava’u, Tonga (18°41.211’S 174°01.139’W).

Etymology. Named for the type locality, Ano Beach, Tonga.

Colour. Body evenly light tan, antenna 2 darker orange.

Habitat. Beach-hoppers occurs on sandy shores under supralittoral wrack or terrestrial plant material.

Description. Based on holotype male, 9 mm, AM P.87313. Head. Eye medium (1/5–1/3 head length). Antenna 1 short, not longer than article 4 of antenna 2 peduncle. Antenna 2 up to half body length; peduncular articles incrassate; article 5 longer than article 4; peduncular articles with many small robust setae. Mandible left lacinia mobilis 5-dentate. Maxilla 1 palp vestigial, 1-articulate. Maxilliped palp article 2 distomedial lobe well developed, article 4 reduced, button-shaped.

Pereon. Gnathopod 1 sexually dimorphic; subchelate; coxa smaller than coxa 2; posterior margin of carpus and propodus each with lobe covered in palmate setae; carpus 2 × as long as propodus, 3.25 × as long as broad; propodus 'subtriangular' with well developed posterodistal lobe, anterior margin with 3 groups of robust setae, lateral surface with 4 cuspidate setae, posterolateral surface with 6 serrate setae, medial surface with 4 cuspidate setae, posteromedial surface with 5 serrate setae; palm slightly obtuse, with 7 serrate setae; dactylus subequal in length to palm. Gnathopod 2 sexually dimorphic; subchelate; gill lobate; basis slightly expanded; ischium with rounded lobe on mid-anterior margin, without posterodistal 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; propodus subrhomboidal, 1.5 × as long as wide; palm slightly acute, reaching about 25% along posterior margin, lined with robust setae, evenly rounded, with weak palmar sinus or notch, without palmar protuberances, posteromedial surface of propodus with groove, with cuticular patch at corner of palm; dactylus slightly longer than palm, spatulate distally; gill bilobate, not incised. Pereopods 2–4 coxae as wide as deep. Pereopods 3–7 cuspidactylate; dactyli with distal patch of many rows of tiny denticles on the anterior margin. Pereopod 4 significantly shorter than pereopod 3; carpus significantly shorter than carpus of pereopod 3; dactylus thickened proximally with a notch midway along posterior margin. Pereopod 5 propodus distinctly longer than carpus. Pereopods 6–7 short (1/3 length of body). Pereopod 6 not sexually dimorphic; slightly shorter than pereopod 7; coxa posterior lobe inner view posteroventral corner rounded, posterior margin perpendicular to ventral margin, posterior lobe without ridge; gill convoluted, coxa not incised. Pereopod 7 not sexually dimorphic; basis lateral sulcus present, slightly pronounced, basis posterior margin with distinct minute serrations, each with a small seta, slight posterodistal lobe present, shallow, broadly rounded; merus and carpus slender; merus posterior margin straight.

Pleon. Pleopods 1–3 well developed; biramous; outer ramus subequal in length to peduncle. Pleopods 1–2 peduncles with sparse marginal robust setae. Pleopod 3 peduncle without marginal setae. Epimeron 2 subequal in length to epimeron 3. Epimeron 3 posterior margin minutely serrate, with minute setae, posteroventral corner with small subacute tooth, ventral margin without robust setae. Uropod 1 not sexually dimorphic, peduncle with 8 robust setae, distolateral robust seta present, small (less than 1/4 length of outer ramus), with simple tip; inner ramus subequal in length to outer ramus, with 3 marginal robust setae; outer ramus without marginal robust setae. Uropod 2 not sexually dimorphic; peduncle with 7–8 robust setae; inner ramus subequal in length to outer ramus, with 4 marginal robust setae; outer ramus with 2 marginal robust setae. Uropod 3 peduncle with 3 robust setae; ramus subequal in length to peduncle, linear (narrowing), with 2 marginal robust setae, with 4–5 apical setae. Telson as broad as long, apically incised, dorsal midline at least halfway, with 7 marginal and apical robust setae per lobe.

Female (sexually dimorphic characters). Based on paratype female, AM P.87314. Antenna 2 peduncular articles slender, with sparse, small robust setae. Gnathopod 1 parachelate; posterior margin of merus, carpus and propodus each without lobe covered in palmate setae; carpus as long as propodus, 3.25 × as long as broad; propodus subrectangular, medial surface with 1 cuspidate seta; palm transverse, without serrate setae; dactylus longer than palm. Gnathopod 2 mitten-shaped; basis expanded anteroproximally; ischium without rounded lobe on mid-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, smooth, lined with serrate setae, without protuberance or shelf near dactylar hinge; without cuticular patch at corner of palm; dactylus subequal in length to palm, not modified distally.

Remarks. The populations of Platorchestia ano from Tonga and from Fiji ( Myers 1985) are very similar. Both have similar palms and similar apical tips on male gnathopod 2. The Fijian population is much larger (15 mm) than the Tongan populations (9 mm), the length to width ratio of the male gnathopod 1 carpus is different (2.2 in the Fijian populations versus 3.2 in the Tongan one) and the telson is about as long as broad in the Tonga population (broader than long in the Fiji population). A molecular analysis of these populations would be informative.

This is the first (group 2) species of Platorchestia from the western Pacific islands. It appears to be most similar to P. jo i Stock & Biernbaum, 1994 from the north-western Pacific coasts of Japan, Korea and Russia. Platorchestia ano differs from P. j o i, mainly in the shape of the palm of male gnathopod 2 which is smooth along the margin with a small proximal sinus (P. j oi has a distinct midmedial sinus).

Distribution. Vava’u, Tonga (current study); Nasese, Suva, Fiji ( Myers 1985).

Figures

FIGURE 1. Platorchestia ano sp. nov., holotype, male, 9 mm, AM P. 87313, Ano Beach, Pangaimotu Island, Vava’u, Tonga. Scale lines for H represents 200 µm; rMD, MP, MX 1 represent 100 µm; and lMD, UL, LL, MX 2 represent 20 µm.

FIGURE 2. Platorchestia ano sp. nov., holotype, male, 9 mm, AM P. 87313, female, AM P. 87314, Ano Beach, Pangaimotu Island, Vava’u, Tonga. Scale lines for male and female G 1 & G 2 represent 100 µm.

FIGURE 3. Platorchestia ano sp. nov., holotype, male, 9 mm, AM P. 87313, Ano Beach, Pangaimotu Island, Vava’u, Tonga. Scale lines for P 3, P 4, P 5 represent 100 µm; P 6, P 7 represent 200 µm.

FIGURE 4. Platorchestia ano sp. nov., holotype, male, 9 mm, AM P. 87313, Ano Beach, Pangaimotu Island, Vava’u, Tonga. Scale lines for U 3 represents 20 µm; EP, Ur, T, U 1, U 2 represent 100 µm.