Ptychognathus ngankeeae, 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 : 286-289

Ptychognathus ngankeeae sp. nov.

( Fig. 12C , 13A–H )

Ptychognathus barbatus .— Poupin & Juncker, 2008:36.— Keith & Marquet, 2011: 62–63 (partim: picture on page 62 only).— Keith et al., 2013: 120–121 (partim: picture on page 120 only).

Type material. Holotype: MNHN-IU-2019-411, ♂, 6.7 mm × 5.8 mm, DNA voucher CA2653 , Vainifao , Futuna, Wallis and Futuna Territory, Station 13, 14°18.461'S, 178°8.564'W, coll. J. Poupin & M. Juncker, 14 October 2007 . Paratype: MNHN-IU-2019-412, 1 ♂, 5.5 mm × 4.7 mm, DNA voucher CA2652 , Leava, Station 15, 14°17.593'S, 178°9.531'W, coll. J. Poupin & M. Juncker, 15 October 2007 .

Diagnosis. Carapace subquadrate, dorsal surface smooth and flat; front broad, anterior margin slightly concave medially; anterolateral margin with 3 teeth including orbital tooth. Merus of third maxilliped with antero-external angle broad; exopod, 1.1–1.3 times broader than ischium. Chelipeds large, symmetrical in males, fingers with a small tuft of setae at tips of pollex; without pulvinus at base of fingers. Merus and carpus of ambulatory legs glabrous.

Description. Carapace ( Fig. 13A ) subquadrate, slightly broader than long, 1.2 in haplotype (1.2 in paratype) times as broad, flat, dorsal surface smooth, glabrous, regions poorly defined, central H-shaped grooves distinct; with noticeable epigastric cristae. Front broad, anterior margin divided into two lobes, slightly concave medially. Frontal width 0.50 (0.47) times CW, fronto-orbital width 0.89 (0.88) times CW. Upper margin of orbit not sinuous. Anterolateral margins and supraorbital margins lined with small granules. 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. Infraorbital ridge consisting of 17 (14) small round granules.

Epistome broad, median part triangular, margin with tiny granules ( Fig. 13B ).

Third maxillipeds ( Fig. 13C ) with ischium subequal in proximal and distal widths, lateral margin concave, ventral surface with longitudinal median ridge. Merus with antero-lateral angle broad; ventral surface with oblique ridge on mesial part. Exopod broad, inflated, greatest width 1.1–1.3, times of median width of ischium.

Chelipeds ( Fig. 13D ) symmetrical in male, not granular at all. Merus without spines longer than broad 2.1 in holotype (1.7 in paratype) times as long as wide, outer lower margin bluntly carinate, smooth. Carpus unarmed, strongly inflated, slightly shorter than wide 1.0 (0.8) times as long as wide; surface of carpus smooth. Outer surface of palm in male smooth, without distinct granules or horizontal ridge, inner surface glabrous, middle part convex. Dactylus distinctly shorter than palm 1.0 (0.7) times as long as palm; inner surface glabrous, terminating in small, hoof-shaped corneous claw, bearing 10 (7) small blunt teeth, pollex, with 4 larger blunt teeth (the two middle teeth are bigger). Proximal half of fingers with long dense soft setae in male. Without pulvinus at base of fingers.

Ambulatory legs (P2–5) comparatively long, slender, somewhat compressed laterally; P4 longest (male: length 1.4 times as long as CW): P5 shortest. Merus elongated, subrectangular in lateral view, unarmed. Anterior and posterior margins of merus of P2–5 glabrous. Anterior and posterior margins of carpus glabrous. Propodus with dense short setae on anterior margins. Ventral surface without rows of short setae. Dactylus terminating in subacute corneous claw, with dense short setae on anterior margins, short and long setae on posterior margins, dorsal and ventral surface with no rows of short setae. P3 ( Fig. 13E ) with merus 2.5 in holotype (2.6 in paratype) times as long as wide, carpus 2.4 (1.6) times as long as wide, propodus 2.0 (1.5) times as long as wide, dactylus 3.7 (3.3) times as long as wide), dactylus 1.0 (1.3) times as long as propodus. P5 ( Fig. 13F ) merus 2.5 in holotype (2.1 in paratype) times as long as wide, carpus 1.9 (1.5) times as long as wide, propodus 1.3 (1.4) times as long as wide, dactylus 2.5 (2.6) times as long as wide), dactylus 0.8 times as long as propodus.

Male pleon ( Fig. 13G ) 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 without tuft of setae. Telson linguiform, terminal margin broadly rounded; length 1.2 times basal width, 1.1 in holotype (1.2 in paratype) times longer than sixth somite, sixth somite 1.3 (1.1) times longer than fifth somite. Female pleon not known.

Male G1 ( Fig. 13H ) slender, 7.6 times as long as wide, slightly curving dorsally reaching suture between thoracic sternite 4 and 5; tip rounded, forming short chitinous structure; subdistal lobe obtuse, partially obscured by stiff setae.

Habitat. In Futuna Island, this species is found with P. similis sp. nov. in rivers in brackish water, near estuaries.

Colouration in life. Body ( Fig. 12C ) and chelipeds yellowish to brownish; inner surface of chela whitish.

Size. Small-sized. The largest male specimen examined is 6.7 mm × 5.8 mm.

Distribution. Ptychognathus ngankeeae sp. nov. is apparently endemic to Futuna Island ( Wallis and Futuna Territory).

Etymology. Named after our late colleague, Ngan Kee Ng, who devoted her life to the study of varunid crabs.

Remarks. Ptychognathus ngankeeae sp. nov. is very similar to P. barbatus (A. Milne-Edwards, 1873) in morphology (see previously, under that species) but it can be distinguished by the absence of a pulvinus at base of fingers of the chelipeds and setae on ambulatory legs (dactylus with short and long setae on posterior margins, dorsal and ventral surface with no rows of short setae (vs dactylus with only dense short setae on posterior margins, dorsal and ventral surface with rows of short setae)).

This new species is also similar to P. stimpsoni Hsu & Shih, 2020 , in morphology, but they can be separated by the absence of a pulvinus at base of fingers of chelipeds (vs pulvinus present; Hsu & Shih 2020: fig. 4E) and setae on ambulatory legs (carpus of ambulatory legs glabrous on anterior margins (vs carpus covered with dense short setae; Hsu & Shih 2020: figs. 4G, H).

Ptychognathus ngankeeae sp. nov. seems to be less common in Futuna than the next new species (see below).

Figures

FIGURE 12. Ptychognathus barbatus (A. Milne-Edwards, 1868): A, dorsal view of a living specimen from New Caledonia (MNHN-IU-2019-210); B, ventral view of the same; D, typical habitat of the species, Wadjana mouth of waterfall, New Caledonia. Ptychognathus ngankeeae sp. nov.: C, dorsal view of a living specimen from Futuna Island. Photo credits: V. de Mazancourt (A, B, D) and J. Poupin (C).

FIGURE 13. Ptychognathus ngankeeae sp. nov.: A, carapace; B, epistome; C, left third maxilliped; D, male cheliped; E, third pereiopod; F, fifth pereiopod; G, male pleon; H, left first gonopod.All from the holotype (MNHN-IU-2019-411).