Ptychognathus barbatus
Creators: name: Mazancourt, Valentin De
name: Mazel, Virgile
name: Marquet, Gérard
name: Poupin, Joseph
name: Keith, Philippe
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Varunidae
Ptychognathus
Ptychognathus barbatus

description: Ptychognathus barbatus (A. Milne-Edwards, 1873)
(Fig. 11A–H, 12A–B)
Gnathograpsus barbatus A. Milne-Edwards, 1873: 316, pl. 17: 4.
Ptychognathus barbatus.— De Man, 1895: 105.— Fransen et al., 1997: 127.
Type material. (All New Caledonia) Syntypes: MNHN-IU-2000-10877 (= MNHN-B10877), 3 ♂ (dry material, mounted on board) 9.0– 9.8 mm × 11.0– 12.7 mm, coll. B. Balansa; MNHN-IU-2000-3395 (= MNHN-B3395), 1 ♂ (dry material), coll. B. Balansa; MNHN-IU-2000-3401 (= MNHN-B3401), 2 ♂ (dry material), coll. B. Balansa; MNHN-IU-2000-3394 (= MNHN-B3394), 2 ♂ (dry material), ♂ 10.0 mm × 12.0 mm, ♂ 9.6 × 11.6 mm, coll. B. Balansa; MNHN-IU-2008-10675 (= MNHN-B12605), 1 ♂ (in ethanol, regenerated dry material), coll. B. Balansa; RMNH-D192, 1 ♂ (12.3 mm × 10.0 mm), coll. B. Balansa; USNM-20308: 3 ♂ (9.5–11.9 mm × 8.0– 9.8 mm), 2 ♀ (9.4–9.6 mm × 7.8 mm), coll. B. Balansa.
Other material examined. NEW CALEDONIA. MNHN-IU-2019-210 (DNA voucher: CA2467), 1 ♂, 9.6 mm × 8.0 mm, Wadjana waterfall, 22°17.603'S, 167°0.859'E, coll. G. Marquet & V. de Mazancourt, 13 September 2018; MNHN-IU-2022-4124, 1 ♂, 8.8 mm × 7.7 mm, Wadjana waterfall, 22°17.603'S, 167°0.859'E, coll. G. Marquet &
V. de Mazancourt, 13 September 2018;MNHN-IU-2017-8250, 3 ♂, 9.4 mm × 8.0 mm to 9.8 mm × 9.1 mm, 2 ♀, 8.7 mm × 7.7 mm, 9.0 mm × 7.9 mm, coll. B. Balansa.
Diagnosis. Carapace subquadrate, dorsal surface smooth, flat; front broad, anterior margin slightly concave medially; anterolateral margin with 3 teeth including orbital tooth. Merus of third maxilliped with anteroexternal angle broad; exopod, 0.7–1.2 times broader than ischium. Chelipeds large, symmetrical in males, fingers with small tuft of setae at tips of pollex. Single pulvinus at base of fingers. Merus and carpus of ambulatory legs glabrous.
Description. Carapace (Fig. 11A) subquadrate, slightly broader than long, 1.2 times as broad as long, flat, dorsal surface smooth and glabrous. Regions poorly defined, central H-shaped grooves distinct; epigastric cristae barely visible. Front broad, anterior margin, divided into 2 lobes, slightly concave medially. Frontal width 0.47–0.51 times CW, fronto-orbital width 0.84–0.90 times CW. Anterolateral margins and supraorbital margins lined with small granules. Upper margin of orbit weakly sinuous. Anterolateral margins each with 3 teeth including orbital tooth; first tooth largest and more distinct, second and third blunt, third tooth indistinct or notch. Posterolateral margins divergent posteriorly, moderately sloping outwards. Lateral and posterolateral margins regularly furnished with short, soft setae.
Third maxillipeds (Fig. 11B) with ischium subequal in proximal and distal widths, lateral margin concave, ventral surface with longitudinal median ridge. Merus with anterolateral angle broad; ventral surface with oblique ridge on mesial part. Exopod broad, inflated, greatest width 0.9–1.2 (♂), 0.7–1.0 (♀) times of median width of ischium.
Male chelipeds (Fig. 11C) symmetrical, not granular at all. Merus longer than broad (length to width ratio 1.1– 2.2); anterior and posterior margins glabrous, posterior distal margins bluntly carinate. Carpus, unarmed, strongly inflated, slightly shorter than wide (length to width ration 0.8–1.0). Palm inflated, smooth, without distinct granules; inner surface glabrous. Fingers with tuft of long setae on outer surface restricted at base of fingers. Dactylus shorter than palm, 0.7–1.0 times as long as palm, terminating in small, hoof-shaped corneous claw bearing 9 or 10 small blunt teeth. Pollex with 4 or 5 larger blunt teeth. Proximal half of fingers with long dense soft setae; single pulvinus at base of fingers.
Female chelipeds (Fig. 11D) distinctly smaller than those of male, chela much narrower than that of male. Fingers with smaller and fewer enlarged teeth. Proximal half of fingers without long dense soft setae; without pulvinus at base of fingers; pollex with ridge consisting of large granules toward palm and ending with distal tuft of setae.
Ambulatory legs (P2–5) comparatively long, slender, somewhat compressed laterally; P4 longest (male: length 1.3–1.4 times carapace width) P5 shortest. Merus elongated, subrectangular in lateral view, unarmed; anterior margins and posterior margins of merus of P2–5 glabrous. Anterior margin of carpus with few short setae, posterior margin glabrous. Propodus with dense short setae on anterior margins and dense short setae and long setae on posterior margins. Ventral surface with rows of short setae. Dactylus terminating in subacute corneous claw, with dense short setae on anterior and posterior margins; dorsal and ventral surface with rows of short setae. P3 merus (Fig. 11E) length to width ratio 1.9–3.3, carpus length to width ratio 1.8–2.1, propodus length to width ratio 1.3–2.0, dactylus length to width ratio 4.1–4.5, dactylus 0.7–1.3 times as long as propodus. P5 merus (Fig. 11F) length to width ratio 2.2–3.3, carpus length to width ratio 1.6–2.6, propodus length to width ratio 1.1–1.9, dactylus length to width ratio 2.6–3.9, dactylus 0.7–0.9 times as long as propodus.
Male pleon (Fig. 11G) narrow, broadly triangular, nearly smooth, distinctly narrowed at base of telson; lateral margins of first to fifth somites nearly straight; margins covered with short setae, distal margin of telson with tuft of setae. Telson linguiform, terminal margin broadly rounded; length 1.1 times basal width, 1.0–1.4 times longer than sixth somite, sixth somite 1.1–1.7 times longer than fifth somite.
Female pleon (Fig. 11H) very broad, covering most of thoracic sternum, fourth somite broadest. Telson broadly subtriangular, terminal margin broadly rounded, length 0.43–0.51 of basal width, 1.1 times longer than sixth somite, sixth somite 1.0–1.1 times longer than fifth somite, measured on midline.
Male G1 (Fig. 11I) slender, 6 times as long as wide, slightly curving dorsally; tip bluntly rounded, forming short chitinous structure; subdistal lobe obtuse, partially obscured by stiff setae.
Colouration in life. Body, chelipeds and legs orange (Fig. 12A and B).
Size. Small-sized. The largest male specimen examined is 9.6 mm × 8.0 mm and the largest female 9.0 mm × 7.9 mm.
Habitat. Ptychognathus barbatus lives on seashores influenced by freshwater flows. Indeed, it was found under rocks on a beach next to the estuary of the Wadjana waterfall in the South Province of New Caledonia (Fig. 12D).
Distribution. Apparently endemic to New Caledonia (Fig. 6).
Remarks. Ptychognathus barbatus is not known from Polynesia but is re-described herein for comparison purposes. It was reported from Banda Aceh (Indonesia) and Penang Island (Malaysia) by De Man (1895: 105–111, fig. 23), from Japan by Sakai (1939: 638–639, text-fig. 348) and from Madagascar by Crosnier (1965: 36–38, figs. 42–45) but this species seems to be in fact restricted to New Caledonia. It can be distinguished from the other species previously reported under this name by features of the frontal region, setae on ambulatory legs and telson of male (see next species).
description: Published as part of Mazancourt, Valentin De, Mazel, Virgile, Marquet, Gérard, Poupin, Joseph & Keith, Philippe, 2024, Integrative taxonomy study of brackish water crabs of the genus Ptychognathus Stimpson, 1858 (Crustacea: Brachyura: Varunidae) from Polynesia, with description of two new species, pp. 267-297 in Zootaxa 5476 (1) on pages 283-286, DOI: 10.11646/zootaxa.5476.1.23, http://zenodo.org/record/12681748