Ptychognathus similis, Mazancourt & Mazel & Marquet & Poupin & Keith, 2024

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, Zootaxa 5476 (1), pp. 267-297 : 289-292

Ptychognathus similis sp. nov.

( Fig. 14A–J , 15A–B )

Ptychognathus hachijoensis .— Poupin & Juncker, 2008: 36, fig. 4c–d; 2010: 75, fig. C.— Keith & Marquet, 2011: 64–65.— Keith et al., 2013: 124–125.

Type material. Holotype: MNHN-IU-2022-4125 (DNA voucher CA2659 ), ♂, 9.3 mm × 7.6 mm, Vainifao River , Futuna, Wallis and Futuna Territory, Station 13, 14°18.461'S, 178°8.564'W, coll. J. Poupin & M. Juncker, 14 October 2007 . Paratypes: MNHN-IU-2022-4126 (DNA voucher CA2658 ), 1 ♀, 7.3 mm × 6.1 mm, 5 ♂ 6.4–7.9 mm × 5.6–6.5 mm, 2 ♀ 7.0–7.2 mm × 5.9–6.3 mm, 2 ♀ ovig. 6.6–7.9 mm × 5.2–7.6 mm, same locality data as for holotype ; MNHN-IU-2022-4127, 4 ♂, 6.5–15.2 × 5.8–13.2 mm, Vai River , Station 3, 14°15.229'S, 178° 9.192'W, coll. N. Charpin & V. Mazel, 6 August 2023 ; MNHN-IU-2022-4128, 2 ♂, 6.4–6.6 × 5.5–5.6 mm, 2 ♀ ovig., 10.9–11.4 × 9.6–9.9 mm, Galoli River , Station 5 14°15.574'S, 178°8.305'W, coll. N. Charpin & V. Mazel, 6 August 2023 ; MNHN-IU-2022-4129, 2 ♂, 13.7–15.3 × 12.5–11.6 mm, 1 ♀, 13.7 × 11.4 mm, Leava River , Station 10, 14°17.598'S, 178°9.543'W, coll. N. Charpin & V. Mazel, 8 August 2023 ; MNHN-IU-2022-4130, 1 ♂, 9.2 × 7.3 mm, Vainifao River , Station 11, 14°17.085'S 178°8.180'W, coll. N. Charpin & V. Mazel, 9 August 2023 ; MNHNIU- 2022-4131, 1 ♂, 14.5 × 12.5 mm, Leava River , Station 20, 14°17.498'S, 178°9.305'W, coll. N. Charpin & V. Mazel, 14 August 2023 .

Comparative material. Ptychognathus hachijoensis Sakai, 1955 ( TAIWAN): MNHN-IU-2022-4001 (DNA voucher CA2866 ), 1 ♂, 9.6 mm × 7.9 mm, 1 ♂, 8.8 mm × 7.3 mm; DNA voucher CA2865 , 1 ♀, 10.2 mm × 9.0 mm, 1 ♀, 10.8 mm × 9.2 mm, Gengfang River estuary, Toucheng, Yilan County, coll. J.-W. Hsu et al.

Diagnosis. Carapace subquadrate, dorsal surface smooth, flat; front broad, anterior margin slightly concave, frontal width 0.45–0.47 times CW; anterolateral margin with single orbital tooth followed by faint lobe. Third maxillipeds with merus anterolateral angle inflated; exopod broad, inflated, greatest width 1.0–1.3 times median width of ischium. Chelipeds stout, symmetrical in males; fingers with tuft of long setae on outer surface restricted at base of fingers; pulvinus at base of fingers. Ambulatory legs slender, somewhat compressed laterally; propodus and dactylus with dense long setae on posterior margins, glabrous on anterior margins.

Description. Carapace ( Fig. 14A ) subquadrate, slightly broader than long, 1.1–1.2 times as broad as long, flat, dorsal surface smooth, glabrous. Regions poorly defined, central H-shaped grooved distinct; epigastric cristae strong. Front broad, anterior margin slightly concave medially frontal width 0.45–0.47 times CW, fronto-orbital width 0.78–0.84 times CW. Anterolateral margins with single orbital tooth, followed by faint lobe. Posterolateral margins divergent posteriorly, moderately sloping outwards. Infraorbital ridge consisting of several small rounded granules, decreasing in size laterally.

Epistome broad ( Fig. 14B ), median part triangular, margin with tiny granules.

Third maxillipeds ( Fig. 14C ) with ischium subequal in proximal and distal widths, lateral margin concave, ventral surface with longitudinal median ridge. Merus broad, with anterolateral angle expanded; ventral surface with oblique ridge on mesial part. Exopod broad, inflated, greatest width 1.2–1.3 times (male), 1.0 (female) of median width of ischium.

Chelipeds ( Fig. 14D ) symmetrical in male, not granular at all. Merus longer than broad (length to width ratio 1.6–1.7), anterior and posterior margins glabrous, posterior distal margins bluntly carinate. Carpus, unarmed, strongly inflated, slightly longer than wide (length to width ratio 1.1–1.2). Palm much inflated, smooth, without distinct granules; inner surface glabrous. Fingers with tuft of long setae on outer surface restricted at the base of fingers. Dactylus as long as palm, terminating in small, hoof-shaped corneous claw, with 9 or 10 small blunt teeth. Pollex with only faint indication of longitudinal groove, with 4 or 5 blunt teeth. Pulvinus at base of fingers.

Female chelipeds ( Fig. 14E ) distinctly smaller than those of male, chela much narrower than that of male. No tuft of setae on outer surface of fingers. Carpus unarmed. Palm not strongly inflated, dactylus distinctly shorter than palm; narrow hiatus between fingers. Two distinct rows of granules on the palm.

Ambulatory legs (P2–5), slender, somewhat compressed laterally; P4 longest (male: length 1.4–1.6 times carapace width, female: length 1.5 times carapace width); P5 shortest. Merus elongated, subrectangular in lateral view, unarmed; anterior margins of merus of P2–4 with long soft setae; posterior margins with sparsely long setae. Anterior and posterior margins of carpus glabrous. Propodus with dense long setae distally on posterior margins and glabrous on anterior margins. Dactylus terminating in subacute corneous claw, with dense long setae on posterior margins and anterior margins glabrous; ventral surface with rows of short setae. P3 merus ( Fig. 14F ) 2.9 in holotype (2.6–3.2 in paratypes) as long as wide, carpus 2.4 (1.7–2.4) as long as wide, propodus 1.9 (2.0–2.7) as long as wide dactylus 6.3 (4.4–5.4) as long as wide, dactylus 0.8 (0.8–0.9) times as long as propodus. P5 merus ( Fig. 14G ) 2.2 in holotype (2.1–2.6 in paratypes) as long as wide, carpus 2.0 (1.9–2.3) as long as wide; propodus 1.3 (1.2–1.5) as long as wide dactylus 3.4 (2.2–2.7) 4 as long as wide, dactylus 1.4 (0.9–1.1) times as long as propodus.

Male pleon ( Fig. 14H ) narrow, broadly triangular, nearly smooth, distinctly narrowed at base of telson; margins without short setae. Telson linguiform, margins without setae, terminal margin broadly rounded; length 1.2 (holotype) (1.3 in paratypes) times basal width, 1.3 (1.4) times long as sixth somite, sixth somite 1.5 (1.3) times longer than fifth somite.

Female pleon ( Fig. 14J ) very broad, covering most of thoracic sternum, fourth somite broadest. Telson broadly subtriangular, terminal margin broadly rounded, length 0.42 times basal width, 1.0 times longer than sixth somite. Sixth somite 1.2–1.3 times longer than fifth somite, measured on midline. Small round eggs 0.26–0.28 mm in diameter.

Male G1 ( Fig. 14I ) slender, 5 times as long as wide, slightly curving dorsally reaching suture between thoracic sternite 4 and 5; tip bluntly rounded, forming short chitinous structure; subdistal lobe obtuse, partially obscured by stiff setae.

Colouration in life. Body and chelipeds ( Fig. 15A ) yellowish to brownish or greyish, sometimes reddish ( Fig. 15B ).

Size. Small-sized. The largest male specimen examined is 9.3 mm × 7.6 mm and the largest ovigerous female 7.9 mm × 7.6 mm.

Habitat. On Futuna Island, this species is found in rivers in brackish water, near estuaries ( Fig. 15C ).

Distribution. Ptychognathus similis sp. nov. seems to be endemic to Futuna Island ( Wallis and Futuna Territory) ( Fig. 6 ).

Etymology. This new species is named after its resemblance to P. hachijoensis .

Remarks. By the anterolateral margins of its carapace having a single orbital tooth followed by a faint lobe, and by the propodus and dactylus of its ambulatory legs having dense, long setae on the anterior margins, Ptychognathus similis sp. nov. is very similar to P. hachijoensis Sakai, 1955 , but it is possible to distinguish them by the width of front (0.45–0.47 times CW vs 0.55–0.56) and by its P5 dactylus (0.8 times as long as propodus vs 1.2).

Figures

FIGURE 6. Distribution map of the species studied. Stars indicate type localities.

FIGURE 14. Ptychognathus similis sp. nov.: A, carapace; B, epistome, C, left third maxilliped; D, male cheliped; E, female cheliped; F, third pereiopod; G, fifth pereiopod; H, male pleon; I, left first gonopod; J, female pleon. Holotype MNHN-IU-2022- 4125 (A–D, F–I) male; paratype MNHN-IU-2022-4126 (E, J) female, both from Futuna.

FIGURE 15. Ptychognathus similis sp. nov.:A, B, dorsal view of specimens from Futuna; C, typical habitat of species, Vainifao River, Futuna. Photo credits: J. Poupin (A), P. Keith (B) and A. Dutartre (C).