Ptychognathus crassimanus Finnegan 1931
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 crassimanus

description: Ptychognathus crassimanus Finnegan, 1931
(Fig. 4A–I, 5A–D)
Ptychognathus crassimanus Finnegan, 1931: 549 [type locality: Marquesas Islands (French Polynesia)].
Ptychognathus crassimanus.— Poupin 1996: 69; 2005: 28 [lists].
Ptychognathus easteranus.— Poupin 1996: 66 (in part, Marquesas only).— Poupin & Corbari 2012: 8 [Marquesas].— Salvat et al. 2016: 244 [Marquesas].—All not P. easteranus Rathbun, 1907 but P. crassimanus Finnegan, 1931.
Material examined. FRENCH POLYNESIA. Marquesas Islands. Fatu Hiva: MNHN-IU-2011-9062 (DNA voucher: CA2646), 1 ♀, 14.0 mm × 11.8 mm, Baie des Vierges, Stn MQ16-M, 10°27.84'S, 138°39.97'W, Expedition PAKAIHI I TE MOANA, coll. MNHN-AAMP, 17–18 January 2012; MNHN-IU-2022-4082 (DNA voucher: CA2647), 1 ♀ ovig., 13.7 mm × 12.4 mm, same collection data as previous. Hiva Oa: MNHN-IU-2022-4083 (DNA voucher: CA2668), 1 ♂, 13.0 mm × 12.5 mm, Ta'aoa River, coll. E. Feunteun, P. Keith, E. Vigneux, 13 February 2000; MNHNIU- 2022-4084 (DNA voucher: CA2669), 1 ♂, 14.0 mm × 13.2 mm, Ta'aoa River,, coll. E. Feunteun, P. Keith, E. Vigneux, 13 February 2000; MNHN-IU-2019-180 (DNA voucher: CA2465), 1 ♂, 9.4 mm × 8.4 mm, Ta'aoa River,
9°50.101'S, 139°03.725'W, coll. E. Feunteun, P. Gerbeaux, G. Marquet, P. Tiberghien, 9 October 2017; MNHN-IU-2019-183 (DNA voucher: CA2464), 1 ♂, 18.2 mm × 15.4 mm, Faakuaa River, 09°46.097'S, 139°01.768'W, coll. E. Feunteun, P. Gerbeaux, G. Marquet, P. Tiberghien, 10 October 2017. Ua Pou: MNHN-IU-2019-182 (DNA voucher: CA2466), 1 ♂, 16.2 mm × 13.8 mm, Hakahetau River, 09°21.600'S, 140°06.313'W, coll. E. Feunteun, P. Gerbeaux, G. Marquet, P. Tiberghien, 16 October 2017; MNHN-IU-2022-4085 (DNA voucher: CA2665), 1 ♂, 9.6 mm × 8.4 mm, Hakahau Bay, coll. J. Poupin, 12 February 1996; MNHN-IU-2022-4086 (DNA voucher: CA2666), 1 ♀ ovig., 9.2 mm × 8.5 mm, Hakahau Bay, coll. J. Poupin, 12 February 1996.
Diagnosis. Carapace quadrate, dorsal surface smooth and flat. Front broad, anterior margin straight to faintly sinuous, frontal width 0.37–0.42 times CW; anterolateral margin with 3 teeth including orbital tooth. Third maxillipeds with auriculiform merus; exopod broad, inflated, greatest width 1.3–1.6 times of median width of ischium. Chelipeds stout, symmetrical in males; inner angle of carpus with single blunt spine only in females; fingers glabrous. Ambulatory legs slender, somewhat compressed laterally; merus with single spine on anterior margins near carpus in P2–4, spine indistinct or absent in P5.
Description. Carapace (Fig. 4A) quadrate, slightly broader than long, 1.1 times as wide as long, flat, dorsal surface smooth and glabrous; regions poorly defined but with central H-shaped grooves clearly discernible. Front broad, anterior margin faintly sinuous; frontal width 0.37–0.42 times CW, fronto-orbital width 0.91–0.96 times CW. Upper border of orbit S-shaped, inner angle with distinct slit. Anterolateral margins and supraorbital margins lined with small granules, anterolateral margins with 3 teeth including orbital tooth, first tooth most distinct and acute, slightly sloping forward, second and third teeth, clearly visible, blunt. Posterolateral margins divergent posteriorly, moderately sloping outwards. Lateral and posterolateral margins furnished with short soft setae.
Third maxillipeds (Fig. 4B) with ischium subequal in proximal and distal widths, lateral margin concave, ventral surface with longitudinal median ridge. Merus very broad, with anterolateral angle strongly inflated, auriculiform; ventral surface with oblique ridge on mesial part. Exopod broad, inflated, greatest width 1.4–1.6 times (male), 1.3–1.4 (female) of median width of ischium.
Male chelipeds (Fig. 4C) symmetrical, not granular at all. Merus longer than broad (length to width ratio 1.8– 2.1, anterior and posterior proximal margins with long soft setae, posterior distal margins bluntly carinate. Carpus strongly inflated, slightly longer than wide (length to width ratio 1.0–1.2); anterior distal angle with single blunt spine only in females. Palm very much inflated (crassimanus means stout palm), outer surface smooth, without distinct granules; inner surface glabrous. Fingers glabrous. Dactylus about as long as palm, terminating in small, hoof-shaped corneous claw, bearing 8–12 small teeth, pollex with only faint indication of longitudinal groove, with 4–8 teeth, more conical and larger than those of dactylus. Without pulvinus at base of fingers.
Female chelipeds (Fig. 4D, 4E) distinctly smaller than those of male, chela much narrower than that of male. Palm not strongly inflated; movable finger distinctly shorter than palm. Carpus with small blunt spine at inner distal angle (Fig. 4E). Narrow hiatus between fingers. Pollex with ridge consisting of large granules toward palm.
Ambulatory legs (P2–5), slender, somewhat compressed laterally; P4 longest (male: length 1.4–1.9 times carapace width, female: length 1.2–1.4 times carapace width); P5 shortest. Merus elongated, subrectangular in lateral view, with single spine on anterior margins near carpus in P2–P4, spine indistinct or absent in P5. Anterior margins of P2–5 meri with long soft setae; posterior margins glabrous. Anterior margin of carpus with dense short setae, posterior margins glabrous. Propodus with dense short setae on anterior margins and dense short setae with sparse long setae on posterior margins. Dactylus terminating in subacute corneous claw, with dense short setae on anterior and posterior margins; ventral surface with rows of short setae. P3 (Fig. 4F) with merus 3.2–3.9 as long as wide, carpus 1.5–2.1 as long as wide, propodus 2.1–2.3 as long as wide, dactylus 3.7–5.2 as long as wide, dactylus 1.0–1.2 times as long as propodus. P5 (Fig. 4G) with merus 2.2–2.8 as long as wide, carpus 1.6–2.5 as long as wide, propodus 1.2–1.6 as long as wide, dactylus 2.5–3.0 as long as wide, dactylus 0.7–0.9 times as long as propodus.
Male pleon (Fig. 4H) narrow, broadly triangular, nearly smooth, distinctly narrowed at base of telson; margins covered with short setae, setae on margins of telson longer. Telson linguiform, terminal margin broadly rounded; length 1.0–1.2 times basal width, 1.1–1.3 times as long as sixth somite, sixth somite 1.1–1.4 times longer than fifth somite.
Female pleon (Fig. 4I, 5C) very broad, covering most of thoracic sternum. Telson broadly subtriangular, terminal margin broadly rounded, length 0.25 times basal width, 0.8–0.9 times longer than sixth somite, sixth somite 1.0–1.2 times longer than fifth somite, measured on midline. Small round eggs 0.25–0.31 mm in diameter.
Male G1 (Fig. 4J) slender, 8 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. Carapace (Fig. 5A) bluish brownish. Chelipeds (Fig. 5B) bluish brownish superiorly and orange inferiorly; finger tips whitish. Ambulatory legs bluish-brown with orange parts.
Size. Medium-sized. the largest male specimen examined is 18.2 mm × 15.4 mm and the largest female 14.0 mm × 11.8 mm.
Habitat. This species is found in brackish water, near estuaries (Fig. 5D).
Distribution. Ptychognathus crassimanus Finnegan, 1931 (Fig. 6) is endemic to the Marquesas Islands (French Polynesia).
Remarks. This species resembles P. easteranus, P. makii Hsu & Shih, 2020 and P. altimanus (Rathbun, 1914) by its broad front, anterolateral margins of carapace with three teeth clearly visible, its P2–4 merus with a single small spine on anterior margin near the carpus. Ptychognathus crassimanus differs from P. altimanus by having a shorter frontal region (vs longer) and posterolateral margins of carapace distinctly divergent posteriorly (vs almost parallel, not divergent posteriorly) (Naruse et al. 2005: fig. 1A). It differs from P. makii by having fewer teeth on the dactylus 8–12 (vs 15) and on the pollex 4–8 (vs 10) (Hsu & Shih 2020: fig. 3D) and merus of ambulatory legs with their posterior margins glabrous (vs with short setae densely and long setae sparsely (Hsu & Shih 2020: fig. 3F). Ptychognathus crassimanus differs from P. easteranus by its stouter P5 dactylus (2.5–3.0 as long as wide vs 3.0–3.9) and its propodus (0.7–1.1 times as long as dactylus vs 0.9–1.4).
For the present study, the type specimen preserved in the Natural History Museum, London (Catalogue no. NHM 1932.12.19.221) was not examined.
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 272-275, DOI: 10.11646/zootaxa.5476.1.23, http://zenodo.org/record/12681748