Ptychognathus amikee Hsu & Shih, 2024, sp. nov.
Creators: name: Hsu, Jhih-Wei
name: Shih, Hsi-Te
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Varunidae
Ptychognathus
Ptychognathus amikee

description: Ptychognathus amikee sp. nov.
(Figs. 1A–D, 2)
Type material. Holotype: male (15.8 × 13.6 mm), MNHN-B29852, Kirilou River, Gaua Island, Vanuatu, coll. Marquet and Keith, 18 July 2005. Paratype: 1 female (17.4 × 14.6 mm), MNHN-B29853, Lembot River, Gaua Island, Vanuatu, 20 July 2005.
Additional material: 1 male (16.1 × 14.0), ZRC 2021.0350, st. VM67, SE Baldwin Cove, Espiritu Santo Island, Vanuatu, coll. SANTO 2006 Marine Biodiversity Survey, 14 Oct. 2006.
Diagnosis. Carapace (Figs. 1A, C, 2A) subquadrate, 1.16–1.19 times as wide as long; dorsal surface glabrous, hepatic region covered with small granules; postfrontal region distinct, separated into two lobes by shallow grooves; front broad, frontal margin almost straight, lined with tiny, rounded granules; anterolateral margins with 2 indistinct teeth behind broad, bluntly triangular external orbital tooth. Third maxillipeds (Fig. 2B) with sparse setae; exopod almost equal in width to ischium. Chelipeds (Figs. 1 A–D, 2C, D) symmetrical; inner surface of palm glabrous; in male, proximal half of fingers with tufts of long dense soft setae on outer surface, slightly extending to palm side; pulvinus present at base of fingers in male but absent in female (Fig. 2C, D). P4 (Fig. 2E) relatively long; propodus with dense short and sparse long setae on distal 1/3–1/2 of posterior margins; dactylus with dense short setae on almost entire, posterior margin. P5 (Fig. 2F) relatively short; propodus covered with dense short and sparse long setae on distal 1/4–1/3 of posterior margins; dactylus with dense short setae each on anterior and posterior margins. Male pleon (Fig. 2G) narrow, distal margin of telson not concave nor with tuft of setae. G1 (Fig. 2I–L) slender, distally curved toward dorsolateral; tip chitinous, with 2 short rounded lobes in lateral view (Fig. 2K, L), opened toward lateral and mesial, respectively. Vulvae (Fig. 2M) with 2 short, rounded sternal vulvar covers.
Description. Carapace (Figs. 1A, C, 2A) subquadrate, 1.16–1.19 times (n=2) as wide as long; dorsal surface flattish, finely punctate, glabrous; regions weakly defined, with noticeable groove between epigastric regions; hepatic region (especially part near anterolateral margin) covered with small granules; metabranchial region sloping outwards. Front broad, slightly convex near orbital regions; frontal margin almost straight, not divided into any distinct lobes, lined with small, rounded granules; postfrontal region distinct, separated into 2 lobes by shallow grooves, margin of lobe lined with minute granules.
Supraorbital margins lined with small granules. Anterolateral margins granulated, with 2 indistinct teeth behind external orbital tooth; external orbital tooth largest, broad, bluntly triangular, slightly sloping forward. Posterolateral margins slightly convergent posteriorly; posterolateral regions almost glabrous. Infraorbital ridge consisting of several small, rounded granules. Epistome broad, median part triangular.
Third maxillipeds (Fig. 2B) broad, with sparse short setae (numerous on exopod) on external surface; merus with oblique shallow groove along mesial margin of external surface, anterolateral angle broadly rounded, slightly sloping laterally; ischium with an indistinct shallow groove slightly mesial to midline of external surface; exopod broad, convex, almost equal in width to ischium.
Chelipeds (Figs. 1 A–D, 2C, D) symmetrical in male and female, stronger in male. Merus without spines, dorsal and inner margins proximally with dense soft setae, ventral margins glabrous. Carpus almost glabrous on surface, only with several tiny granules; inner distal angle blunt, without any spines. In male, palm (Fig. 2C) finely punctate, without distinct granules on outer surface; inner surface glabrous, slightly convex medially. Movable finger (dactylus) approximately as long as palm, cutting edge with 8–10 small blunt teeth; immovable and movable fingers almost equal in length, cutting edge with 4 or 5 large blunt teeth; proximal halves of movable and immovable fingers with long dense soft setae, slightly extending to palm side, pulvinus present at base of fingers. In female, outer surface of palm (Fig. 2D) glabrous, with prominent ridge consisting of small granules running parallel to ventral margin; inner surface almost glabrous, only with sparse short setae.
Ambulatory legs (Figs. 1A–D) slender, P3 and P4 equal in length, longest; setation not different between male and female. Meri without spines, but with long soft setae on proximal half of anterior margin; posterior margins almost glabrous; lateral dorsal surfaces glabrous. P2 relatively short; propodus covered with dense short setae on anterior margin and ventral surface; dorsal surface glabrous, anterior margins of distal half covered with dense short and sparse long setae; dactylus covered with rows of short setae on margins and surface. P3 and P4 (Figs. 1A–D, 2E) relatively long; meri ca. 2.7 as long as wide (holotype); carpi glabrous on margins and surfaces; propodi ca. 1.9 as long as wide (holotype), glabrous on anterior margin and dorsal surface, part near posterior margin of ventral surface covered with dense short setae in P3 but almost glabrous in P4, posterior margins with dense short and sparse long setae on distal 1/3–1/2; dactyli equal to propodi in length, with dense short setae on anterior and posterior margins. P5 (Fig. 2F) relatively short; merus ca. 2.6 as long as wide (holotype); carpus ca. 1.3 as long as wide (holotype), glabrous on margins and surfaces; propodus covered with dense short setae near distal of dorsal surface (denser on distal part), posterior margin with dense short setae and sparse long setae on distal 1/4–1/3; dactylus ca. 0.8 times as long as propodus (holotype), with dense short setae on anterior and posterior margins.
Male pleon (Fig. 2G) narrow; external surface smooth, without any granules; lateral margins lined with short setae; telson tongue-shaped, significantly longer and narrower than sixth pleonal segment, distal margin of telson not concave, without tuft of setae. Female pleon (Fig. 2H) wide; external surface smooth, without any granules; lateral margins lined with short setae; telson bluntly triangular, almost equal to sixth pleonal segment in length.
Male G1 (Fig. 2I–L) slender, slightly curved, distally curved toward dorsolateral; tip chitinous, with 2 short rounded lobes in lateral view (Fig. 2K, L), opened toward lateral and mesial, respectively; G2 shorter than 1/4 length of G1.
Female vulvae (Fig. 2M) with 2 short, rounded sternal vulvar covers; sunken on mesial part.
Etymology. The new species is named after the late Dr. Ngan Kee Ng for her contribution to the taxonomy of brachyurans, especially the family Varunidae (cf. Lee & Jaafar 2022). The name “amikee ” is an arbitrary combination of friend (amicus or amica) and ‘Kee’.
Size. Largest male 15.8 × 13.6 mm (MNHN-B29852); largest female 17.4 × 14.6 mm (MNHN-B29853).
Distribution. At present, only known from Vanuatu.
Remarks. Ptychognathus amikee sp. nov. is morphologically similar to P. demani Roux, 1917, P. intermedius (De Man, 1879), and P. pilipes (A. Milne-Edwards, 1868) in the blunt anterolateral teeth and the postfrontal region of carapace with separated into two distinct lobes, but can be distinguished by the other features of carapace, and the distribution of long setae on male chelipedal palm and fingers, and ambulatory legs in both sexes. However, the character of G1 among those species compared is very similar and not useful to separate them.
Ptychognathus amikee sp. nov. and other three species differ in male chelipedal palm and immovable finger, and ambulatory legs in both sexes. The outer surface of male palm is nearly smooth, and the proximal halves of movable and immovable fingers of the cheliped are covered with dense long setae in P. amikee (Fig. 2C) [vs. setae present only on the proximal half of immovable finger in P. demani (Roux 1917: 615, pl. 18 fig. 20); small granules present and no dense setae in P. intermedius (De Man 1879: 69; De Man 1892: tab. 19, fig. 10a); granules and glabrous in P. pilipes (A. Milne-Edwards, 1868: 184, pl. 27 (9))]. The anterior margins of carpi and propodi of ambulatory legs in both sexes are almost glabrous and only distal part of P5 carpus has dense short setae in P. amikee (Fig. 2E, F) [vs. anterior margins of carpi and propodi with dense short setae in P. demani (Roux 1917: 615, pl. 18 fig. 18); anterior and posterior margins of propodi with dense long setae in P. intermedius (De Man 1879: 70; De Man 1892: 323); anterior and posterior margins of carpi, propodi and dactyli with dense long setae in P. pilipes (A. Milne-Edwards, 1868: 184, pl. 27 (6)].
This new species is also similar to P. barbatus, P. hachijoensis, P. pusillus, P. sakaii, and P. stimpsoni in having similar distribution of setae in male chelipedal palm and fingers, i.e., proximal halves of both fingers with long setae, but can be separated by the frontal margin of carapace; it is almost straight in P. amikee sp. nov. (Fig. 2A), instead of concave medially in the other species [A. Milne-Edwards 1873: 136, pl. 17(4); De Man, 1905: 539, pl. 17(1–2); Hsu & Shih 2020: figs. 2C, E, 4A; Hsu et al. 2022b: figs. 1, 2A, 3A].
description: Published as part of Hsu, Jhih-Wei & Shih, Hsi-Te, 2024, A new species of the genus Ptychognathus Stimpson, 1858 (Crustacea: Brachyura: Varunidae) from Vanuatu, pp. 152-165 in Zootaxa 5476 (1) on pages 154-156, DOI: 10.11646/zootaxa.5476.1.15, http://zenodo.org/record/12724142