Ptychognathus riedelii (A. Milne-Edwards, 1868 )

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 : 280-283

Ptychognathus riedelii (A. Milne-Edwards, 1868)

( Fig. 9A–H , 10A–B )

Gnathograpsus Riedelii A. Milne-Edwards, 1868: 182 , pl. 27, figs 1–5 [type locality: Sulawesi (Celebes), Indonesia]. Ptychognathus riedelii riedelii .— De Man, 1892: 323.

Ptychognathus riedelii .— Tesch, 1918: 87.— Cai & Ng 2001: 686, fig. 16.

Ptychognathus andamanica Alcock, 1900: 404 , pl. LXV, figs 3, 3a.

Type material. Syntypes: MNHN-IU-2000-3402 (= MNHN-B3402 ), 1 ♂, dry specimen, 23.2 mm × 20.4 mm, Sulawesi, Indonesia, coll. M. Riedel ; MNHN-IU-2000-3627 (= MNHN-B MNHN-3627 ): 2 ♂ and 1 ♀, dry specimens, Sulawesi, Indonesia, coll. M. Riedel.

Other material examined. SAMOA. Upolu: MNHN-IU-2022-4114 (DNA voucher: CA2660 ), 1 ♂, 26.7 mm × 26.27; MNHN-IU-2019-8 (DNA voucher: CA2492 ), 1 ♂, 20.8 mm × 17.9 mm, Pineula River , 14°01.780'S, 171°37.003'W, 20 m a.s.l., coll. P. Gerbeaux, G. Marquet & P. Keith 25 July 2004 . INDONESIA. Papua: MNHNIU- 2018-2965 (DNA voucher: CA2491 ), 1 ♂, 19.5 mm × 16.9 mm, SIG 99; MNHN-IU-2018-2643 (DNA voucher: CA2490 ), 1 ♂, 17.3 mm × 15.1 mm, SIG11 . PAPUA NEW GUINEA. New Britain: MNHN-IU-2018-2967 (DNA voucher: CA2456 ), 1 ♀, 14.2 mm × 12.6 mm, Gavuvu river , 05°28.733'S, 150°23.557'E, coll. R. Causse, P. Keith, C. Lord, P. Amick, 27 October 2018 . SOLOMON ISLANDS. Choiseul: MNHN-IU-2018-4124 (DNA voucher: CA2489 ), 1 ♂, 16.2 mm × 14.6 mm; MNHN-IU-2022-4115, 1 ♂, 13.3 mm × 10.8 mm, Lopakare, 07°01.613'S, 156°46.567'E, coll. P. Gerbeaux, P. Keith, G. Marquet, 20 October 2014; MNHN-IU-2018-4132 (DNA voucher: CA2482 ), 1 ♂, 22.4 mm × 18.8 mm; MNHN-IU-2022-4116, 2 ♂, 10.3–21.0 mm × 9.4–17.8 mm and 2 ♀, 13.7–17.6 mm × 12.7–15.6 mm, Lopakare , 07°01.834'S, 156°45.789'E, coll. P. Gerbeaux, P. Keith, G. Marquet, 21 October

2014. Kolombangara : MNHN-IU-2018-2647 (DNA voucher: CA2483 ), 1 ♂, 10.0 mm × 8.9 mm, Pointete River, 07°52.413'S, 157°07.982'E, coll. P. Keith, C. Lord, G. Marquet, 15 November 2015 ; MNHN-IU-2018-4129 (DNA voucher: CA2486 ), 1 ♂, 21.3 mm × 16.6 mm, Vanga 1 River, 07°55.172'S, 156°57.798'E, coll. P. Keith, C. Lord, G. Marquet, 18 November 2015 ; MNHN-IU-2018-4120 (DNA voucher: CA2488 ), 1 ♂, 19.2 mm × 17.1 mm; MNHNIU- 2022-4117, 1 ♂, 11.7 mm × 10.5 mm and 1 ♀, 11.8 mm × 10.7 mm, Liva River , 08°03.881'S, 157°10.421'E, coll. P. Keith, C. Lord, G. Marquet, 11 November 2015 ; MNHN-IU-2018-2651 (DNA voucher: CA2487 ), 1 ♂, 11.8 mm × 9.6 mm, Pipiro River , 07°53.083'S, 157°08.195'E, coll. P. Keith, C. Lord, G. Marquet, 13 November 2015 . Vella Lavella : MNHN-IU-2018-2645 (DNA voucher: CA2484 ), 1 ♀, 10.8 mm × 10.0 mm; MNHN-IU-2022-4118: 1 ♀, 9.7 mm × 9.2 mm, Vala Kadju River , 07°49.860'S, 156°42.644'E, coll. C. Lord & P. Keith, 28 October 2016 ,; MNHN-IU-2018-4128 (DNA voucher: CA2485 ), 1 ♂, 18.6 mm × 17.1 mm; MNHN-IU-2022-4119: 1 ♀, 12.7 mm × 12.1 mm, Maravai River , 07°51.703'S, 156°41.648'E, coll. C. Lord & P. Keith, 31 October 2016 . VANUATU. Efate : MNHN-IU-2018-41.768'E (DNA voucher: CA2493 ), 1 ♂, 20.1 mm × 16.7 mm, Epaule River, 17°33.992'S, 168°27.609'E, coll. P. Feutry, P. Keith, D. Kalfatak, C. Lord, L. Taillebois, 4 February 2010 . Pentecost : MNHNIU- 2019 (DNA voucher: CA2494 ), 1 ♂, 17.6 mm × 15.1 mm; MNHN-IU-2022-4120: 2 ♂, 12.1–14.9 mm × 11.1– 13.0 mm, Bay Omo River, coll. P. Feutry, P. Keith, D. Kalfatak, C. Lord, L. Taillebois, 26 January 2010 . Santo : MNHN-IU-2022-4121 (DNA voucher: CA2456 ), 1 ♂, 14.6 mm × 12.8 mm; MNHN-IU-2022-4122 (DNA voucher: CA2457 ), 1 ♀, 14.6 mm × 12.8 mm; MNHN-IU-2022-4123: 1 ♀, 14.9 mm × 13.0 mm, Sarataka River, 15°30.060'S, 167°9.259'W, coll. D. Kalfatak, P. Keith & G. Marquet, 25 July 2003 .

Diagnosis. Carapace quadrate, dorsal surface smooth and flat; front broad, anterior margin slightly concave medially; anterolateral margin with 3 teeth including orbital tooth. Third maxilliped merus, with anterolateral angle strongly inflated, auriculiform; exopod 1.6–2.6 times broader than ischium. Chelipeds large, glabrous, symmetrical in males, fingers with small tuft of setae at tip of pollex. Ambulatory legs with margins setose.

Description. Carapace ( Fig. 9A ) quadrate, slightly broader than long, 1.1 times as wide as long, flat, dorsal surface smooth and glabrous. Regions poorly defined, central H-shaped grooves distinct. Front broad, anterior margin faintly sinuous; frontal width 0.39–0.45 times CW; fronto-orbital width 0.79–0.86 times CW. Upper margin of orbit sinuous. Anterolateral margins and supraorbital margins lined with small granules, each with 3 teeth including orbital tooth; blunt first tooth, largest and more distinct, second and third teeth, less distinct especially the third. Posterolateral margins divergent posteriorly, moderately sloping outwards.

Third maxillipeds ( Fig. 9B ) 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 very broad, inflated, greatest width 2.1–2.6 times (♂), 1.6–1.9 (♀) of median width of ischium.

Male chelipeds ( Fig. 9C ) symmetrical, not granular at all. Merus longer than broad (length to width ratio 1.3– 1.7), anterior and posterior margins glabrous, posterior distal margins bluntly carinate, directed outward. Carpus, unarmed, strongly inflated, slightly longer than wide (length to width ration 1.0–1.2). Palm inflated, outer surface smooth, without distinct granules; inner surface glabrous. Fingers glabrous except a very characteristic small tuft of setae at tip of pollex. Dactylus distinctly longer than palm, terminating in small, hoof-shaped corneous claw, bearing 10–12 small teeth. Pollex with 5 or 6 teeth, more conical and are larger than those of the dactylus. Without pulvinus at base of fingers.

Female chelipeds ( Fig. 9D ) distinctly smaller than those of male, chela much narrower than in male. Dactylus distinctly shorter than palm, terminating in small, hoof-shaped corneous claw. Fingers with smaller and fewer large teeth. Palm not strongly inflated, outer surface very reticulate-granular; outer surface of palm and pollex outlined near its lower border by fine raised granular line; with characteristic small tuft of setae at tips of pollex as in male.

Ambulatory legs (P2–5), slender, somewhat compressed laterally; P4 longest (♂: length 1.4–1.6 times carapace width, ♀: length 1.4–1.5 times carapace width); P5 shortest. Merus elongated, subrectangular in lateral view, unarmed.Anterior margin of merus of P2–5 with long soft setae; posterior margins with sparsely long setae.Anterior margin of carpus with dense short setae, posterior margins glabrous. Propodus with dense short setae and sparsely long setae on anterior margins and posterior margins. Ventral surface with rows of short setae. Dactylus terminating in subacute corneous claw, with short setae on anterior and posterior margins ventral surface with rows of short setae. P3 merus ( Fig. 9E ) 3.6–4.2 as long as wide, carpus 1.9–2.1 as long as wide, propodus 1.9–2.6 as long as wide dactylus 5.5–7.4 as long as wide, dactylus 0.9–1.2 times as long as propodus. P5 merus ( Fig. 9F ) 3.3–3.5 as long as wide, carpus 1.7–2.7 as long as wide; propodus 1.2–2.0 as long as wide dactylus 3.3–5.1 as long as wide, dactylus 0.6–0.9 times as long as propodus.

Male pleon ( Fig. 9G ) 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 0.9–1.1 times basal width, 0.9–1.0 times long as sixth somite, sixth somite 1.1–1.2 times longer than fifth somite.

Female pleon ( Fig. 9H ) very broad, covering most of thoracic sternum, fourth somite broadest, telson broadly subtriangular, terminal margin broadly rounded, length 0.6–0.7 times basal width, 0.9–1.0 times longer than sixth somite, sixth somite 1.1–1.2 times longer than fifth somite, measured on midline.

Male G1 ( Fig. 9I ) 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 ( Fig. 10A ) brownish green to dark brown. Chelipeds ( Fig. 10B ) rather reddish.

Size. Large-sized.The largest male specimen examined is 22.4 mm × 18.8 mm and the largest non-ovigerous female 14.2 mm × 22.6 mm.

Habitat. Ptychognathus riedelii is a true freshwater species, not collected in brackish waters.

Distribution. Ptychognathus riedelii occurs ( Fig. 6 ) in Indonesia, Philippines, Papua New Guinea (New Britain), Solomon Islands, Vanuatu and Samoa Independent State (Upolu).

Remarks. This large species is easily recognizable by its very characteristic small tuft of setae at tips of pollex, both in males and females.

Figures

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

FIGURE 9. Ptychognathus riedelii (A. Milne-Edwards, 1868): A, carapace; B, left third maxilliped; C, male cheliped; D, female cheliped; E, third pereiopod; F, fifth pereiopod; G, male pleon; H, female pleon; I, right male first gonopod. MNHN- IU-2022-4114 (A–C, E–G) male from Samoa; MNHN-IU-2019-8 (I) male from Samoa; MNHN-IU-2018-2967 (D, H) female from New Britain.

FIGURE 10. Ptychognathus riedelii (A. Milne-Edwards, 1868): A, dorsal view of a living specimen from Kolombangara Island; B: front view of the same. Photo credits: P. Keith.