Ptychognathus easteranus Rathbun 1907
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 easteranus

description: Ptychognathus easteranus Rathbun, 1907
(Figs. 7A–I, 8A–B, 16A, B, D)
Ptychognathus easterana Rathbun, 1907: 31, pl. 2, fig. 4, pl. 7: 4,4a [type locality: Easter Island].
Ptychognathus easteranus. — Tesch, 1918: 86; Garth: 1973.— Poupin, 2003: 31.— Keith et al., 2002: 70–71 (partim).— Keith, 2013: 122–123 (partim).— Poupin & Juncker, 2010: 74–75.
Not Ptychognathus easteranus. —All Marquesas Islands records, attributed herein to P. crassimanus (see under that species).
Ptychognathus intermedius.— Ortmann, 1894: 711 (Tahiti). [Not Ptychognathus intermedius (De Man, 1879)].
Type material. Holotype: USNM 32845, ♂, 10.8 mm × 12.6 mm, Easter Island, Chile, coll. R/V Albatross, 20 December 1904.
Other material examined. COOK ISLANDS. Rarotonga (no specimens collected, observations only): Avana River, station 7, 21°14.808'S, 159°43.796'W, 13 July 2010; Aratiu River, 21°12.562'S, 159°47.280'W, 14 July 2010; Takavainé River, 21°12.562'S, 159°46.485'W, 14 July 2010; Murivai River, 21°14.802'S, 159°49.726'W, 15 July 2010. FRENCH POLYNESIA. Gambier archipelago. Mangareva: MNHN-IU-2022-4087 (DNA voucher: CA2670), 1 ♂, 15.0 mm × 12.2 mm; MNHN-IU-2022-4088 (DNA voucher: CA2671), 1 ♀ ovig, 9.4 mm × 7.5 mm; MNHNIU- 2022-4089, 8 ♂, 8.4–13.9 mm × 7.2–11.9 mm, 2 ♀ ovig, 8.4–8.5 mm × 7.0– 7.1 mm. Austral archipelago. Rapa: MNHN-IU-2022-4090 (DNA voucher: CA2654), 1 ♂, 13.5 mm × 12.1 mm; MNHN-IU-2022-4091(DNA voucher: CA2655), 1 ♂, 14.3 mm × 12.7 mm; MNHN-IU-2022-4092, 5 ♂, 10.7–13.7 mm × 9.1–11.8 mm; 5 ♀, 6.2–9.1 mm × 5.6–8.1 mm; 1 ♀ ovig, 11.4 mm × 9.7 mm, Ahurei Bay, coll. J. Poupin, 8 November 2002; MNHN-IU-2022-4093, 3 ♂, 8.0– 14.7 mm × 7.4–14.2 mm, coll. J.C. Guéry, G. Marquet, July 2001; MNHN-IU-2022-4094 (DNA voucher: CA2672), 1 ♂, 11.1 mm × 10.5 mm; MNHN-IU-2022-4095, 1 ♂, 9.4 mm × 8.4 mm (DNA voucher: CA2673), 7 ♂, 9.8–12.2 mm × 8.3–10.6 mm, 3 ♀, 6.9–8.1 mm × 5.8–7.01 mm, Ahurei Bay, coll. J. Poupin, 19–21 March 1995; MNHN-IU-2022-4096, 8 ♂, 7.1–14.0 mm × 6.3–12.4 mm, 2 ♀ ovig, 10.8–12.5 mm × 9.9–11.2 mm; 4 ♀, 6.6–8.8 mm × 5.8–7.4 mm, coll. J. Poupin, 8 November 2002; MNHN-IU-2022-4097 (DNA voucher: CA2667), 1 ♂, 13.7 mm × 14.6 mm; MNHN-IU-2022-4098, 3 ♂, 8.4–14.0 mm × 7.2–11.3 mm, 2 ♀, 7.9–11.6 mm × 7.3–10.5 mm, coll. J. C. Guéry & G. Marquet, July 2001. Rurutu: MNHN-IU-2019-179 (DNA voucher: CA2478), 1 ♂, 14.9 mm × 12.2 mm; MNHN-IU-2022-4099, 4 ♂, 8.1–13.8 mm × 6.5–11.2 mm, 3 ♀, 8.3–10.41 mm × 7.3–9.0 mm, "two rivers", coll. T. Robinet, 14 July 2007. Society Archipelago. Tahiti: MNHN-IU-2022-4100, 10 ♂, 6.4–15.4 mm × 5.7–13.8 mm, Papenoo River, sample 11, coll. V. Mazel, 6 February 2019; MNHN-IU-2022-4101 (DNA voucher: CA2717), 1 ♂, 17.1 mm × 14.5 mm; MNHN-IU-2022-4102, 6 ♂, 8.4 –12.4 mm × 7.6–11.1 mm, 2 ♀, 8.5–9.1 mm × 7.5–8.1 mm, Papenoo River, sample 9, coll. V. Mazel, 7 February 2019; MNHN-IU-2022-4103 (DNA voucher: CA2716), 1 ♂, 13.9 mm × 11.7 mm, Papenoo River, sample 1, coll. V. Mazel, 28 January 2020; MNHN-IU-2022- 4104, 2 ♂, 9.4–12.4 mm × 8.7–11.2 mm, 3 ♀, 7.3–9.2 mm × 6.7–8.1 mm, Papenoo River, sample 5, coll. V. Mazel, 26 January 2020; MNHN-IU-2022-4105, 2 specimens, 14.0–15.0 mm × 11.9– 11.9 mm, Papenoo River, sample 4, coll. V. Mazel, 24 January 2020; MNHN-IU-2022-4106, 7 ♂, 8.3–15.3 mm × 7.5–14.2 mm, 2 ♀, 6.5–8.9 mm × 5.4–7.7 mm, Papenoo River, sample 9, coll. V. Mazel, January 2020; MNHN-IU-2016-11891, 1 ♂, 9.6 mm × 12.5 mm, 1 ♀, 14.8 mm × 12.5 mm, Papenoo River, sample 2, coll. V. Mazel, 11 March 2019; MNHN-IU-2022-4107, 1 ♂, 13.5 mm × 11.4 mm, Papenoo River, sample 1, coll. V. Mazel 12 January 2020; MNHN-IU-2022-4108, 2 ♂, 8.5 mm × 7.6 mm, 11.2 mm × 10.3 mm, Papenoo River, sample 2, coll. V. Mazel, 11 November 2020; MNHN-IU-2016- 11889, 1 ♂, 17.2 mm × 14.8 mm, Papenoo River, sample 1, coll. V. Mazel, 12 March 2021; MNHN-IU-2022-4109 (DNA voucher: CA2645), 1 ♂, 16.5 mm × 14.7 mm; MNHN-IU-2022-4110, 1 ♂, 6.0 mm × 5.3 mm, 1 ♀, 6.9 mm × 5.9 mm, Papenoo River, sample 3, coll. V. Mazel, 14 March 2021; MNHN-IU-2022-4111, 2 ♂, 13.4–15.7 mm × 11.8–13.7 mm, Papenoo River, sample 9, coll. V. Mazel, 11 January 2021; MNHN-IU-2022-4112, 1 ♂, 12.0 mm × 10.6 mm, Papenoo River, sample 1, coll. V. Mazel, 18 December 2020; MNHN-IU-2022-4113 (DNA voucher: CA2644), 1 ♂, 15.0 mm × 12.0 mm, Papenoo River, sample 11, coll. V. Mazel, 15 January 2021.
Comparative material. Ptychognathus intermedius De Man, 1879, RMNH. CRUS.D.194, syntype male 55.2 × 46.9 mm, Moluccas (Indonesia) (photo only, fig. 16C).
Diagnosis. Carapace quadrate, dorsal surface smooth and flat. Front broad, anterior margin faintly sinuous, frontal width 0.37–0.42 times CW; anterolateral margin with 3 teeth including orbital tooth. Third maxillipeds with auriculiform merus and 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. 7A) quadrate, slightly broader than long, 1.1 times as broad as long, flat, dorsal surface smooth and glabrous. Regions poorly defined; central H-shaped grooves clearly discernible. Front broad, anterior margin faintly sinuous. Frontal width 0.37–0.42 times CW. Fronto-orbital width 0.89–0.96 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 tree 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. 7B) 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 1.7–1.9 times (male), 1.4–1.6 (female) of median width of ischium.
Male chelipeds (Fig. 7C) symmetrical, not granular at all. Merus longer than broad (length to width ratio 1.8– 2.0, 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 1.0–1.4); anterior distal angle with single blunt spine only in females. Palm inflated 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 8–10 small teeth, pollex with 4 or 5 teeth, more conical and larger than those of dactylus. Without pulvinus at base of fingers.
Female chelipeds (Fig. 7D) distinctly smaller than those of male, chela much narrower than that of male. Palm not strongly inflated; dactylus distinctly shorter than palm. Carpus with small blunt spine at dorsodistal angle. Narrow hiatus between fingers. Distally numerous short setae on the fingers. Distinct rows of granules on fingers and palm.
Ambulatory legs (P2–5), slender, somewhat compressed laterally; P4 longest (male: length 1.4–1.5 times carapace width, female: length 1.5 times carapace width); P5 shortest. Merus elongated, subrectangular in lateral view, with single spine on anterior margins near carpus in P2–4, spine indistinct or absent in P5. Anterior margins of meri of P2–5 with long soft setae; posterior margins with long setae sparsely. Anterior margins of carpus with dense short setae and long setae sparsely, posterior margins glabrous. Propodus with dense short setae and sparse long setae on anterior margins and only dense short 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; ventral surface with rows of short setae. P3 merus (Fig. 7F) 2.8–3.9 as long as wide, carpus 1.6–2.0 as long as wide, propodus 2.1–2.5 as long as wide, dactylus 3.4–5.9 as long as wide and1.1–1.3 times as long as propodus. P5 merus (Fig. 7G) 2.6–2.9 as long as wide, carpus 1.5–2.0 as long as wide, propodus 1.4–1.6 as long as wide dactylus 3.0–3.9 as long as wide and 0.9–1.4 times as long as propodus.
Male pleon (Fig. 7H) 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 1.0–1.1 times basal width, 1.1–1.2 times long as sixth somite, sixth somite 1.1–1.2 times longer than fifth somite.
Female pleon (Fig. 7I) very broad, covering most of thoracic sternum, fourth somite broadest. Telson broadly subtriangular, terminal margin broadly rounded, length 0.29 times basal width, 1.0 times longer than sixth somite, sixth somite 1.0–1.2 times longer than fifth somite, measured on midline. Small round eggs 0.27–0.30 mm in diameter.
Male G1 (Fig. 7J) slender, 6 times as long as wide, straight; tip slightly acute, forming short chitinous structure; subdistal lobe obtuse, partially obscured by stiff setae.
Colouration in life. Carapace (Fig. 8A) bluish–brown. Chelipeds (Fig. 8B) bluish-brown superiorly and orange inferiorly. Fingers tips whitish. Ambulatory legs bluish-brown with orange parts.
Size. Medium-sized. The largest male specimen examined measures 17.2 mm × 14.8 mm and the largest female 14.8 mm × 12.5 mm.
Habitat. In French Polynesia and Rarotonga, this species (Fig. 8C) is found in brackish water, near estuaries.
Distribution. Ptychognathus easteranus occurs (Fig. 6) in the Cook Islands (Rarotonga), French Polynesia (Mangareva in the Gambier archipelago; Rapa and Rurutu in the Austral archipelago, Tahiti and Moorea in the Society archipelago) and Easter Island.
Remarks. Ptychognathus easteranus resembles P. crassimanus, 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 meri with single small spine on anterior margin near carpus. Ptychognathus easteranus 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 its fewer and stronger teeth on the fingers: 9 or 10 for the mobile finger (vs 15; Hsu & Shih 2020: fig. 3D), 4 or 5 for the fixed finger (vs 10 Hsu & Shih 2020: fig. 3D). For the distinctions from P. crassimanus, see above.
Ortmann (1894: 711) reported a specimen of Ptychognathus intermedius (De Man, 1879) from Tahiti. This specimen, deposited in Strasbourg Zoological Museum (MZS) has been reexamined and compared herein with the type specimen of P. intermedius (Fig. 16C) from the Moluccas. It appears in fact to be typical P. easteranus, with its type illustrated alongside in the same figure (Fig. 16D). Therefore, P. intermedius is removed from the Polynesian fauna, its distribution being limited to its type locality in the Moluccas (Indonesia).
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 276-279, DOI: 10.11646/zootaxa.5476.1.23, http://zenodo.org/record/12681748