Ptychognathus sakaii, Hsu & Shih & Li, 2022

Hsu, Jhih-Wei, Shih, Hsi-Te & Li, Jheng-Jhang, 2022, Description of a new species of brackish-water crab of the genus Ptychognathus Stimpson, 1858 (Crustacea: Brachyura: Varunidae) from southern Taiwan, Nauplius (e 2022002) 30, pp. 1-11 : 3-7

publication ID	https://doi.org/ 10.1590/2358-2936e2022002
DOI	https://doi.org/10.5281/zenodo.10912005
persistent identifier	https://treatment.plazi.org/id/D57C1173-4B26-BF34-3311-F9FE360E5131
treatment provided by	Felipe
scientific name	Ptychognathus sakaii
status	sp. nov.

Treatment

Ptychognathus sakaii View in CoL sp. nov.

( Figs. 1−2 View Figure 1 View Figure 2 )

Zoobank: urn:lsid:zoobank.org:act:BB270821-F221-4BB5-AA00-7012BFF47C68

Ptychognathus sp. — Hsu and Shih, 2020: 59, tab. 1.

Material examined. Holotype: male (6.7 × 5.5 mm), NCHUZOOL 17047, Dingtanzih, Hengchun, Pingtung, Taiwan, coll. J.-J. Li, 3 Apr. 2019 . Paratypes: 3 males (5.7 × 5.0 mm; 6.0 × 5.2 mm; 6.7 × 5.5 mm), 1 ovigerous female (5.9 × 5.2 mm), NCHUZOOL 16503, same data as holotype .

Diagnosis. Carapace subquadrate, slightly broader than long, f lat; dorsal surface smooth, glabrous, with noticeable groove between epigastric regions. Front broad, frontal margin lined with small, rounded granules, concave medially in dorsal view, slightly divided into indistinct two lobes.Anterolateral margin with 1 or 2 teeth behind external orbital tooth. Third maxillipeds broad, exopod almost equal to ischium. Chelipeds symmetrical in both sexes; proximal half of fingers of male with long dense soft setae, with single small pulvinus at base of fingers; both long dense soft setae and pulvinus absent in female. Ambulatory legs slender, distoanterior part of carpus distinctly compressed. Male pleon narrow. Distal margin of telson not concave, without tuft of setae. Male G1 slender, almost straight; G2 shorter than 1/4 length of G1.

Description. Carapace ( Figs. 1 View Figure 1 , 2A View Figure 2 ) subquadrate, slightly broader than long, 1.14–1.21 times (n = 5) as broad as long, f lat; dorsal surface smooth, glabrous (except for metabranchial region), regions weakly defined, with noticeable groove between epigastric regions, metabranchial region weakly sloping outwards. Front broad, weakly sloping forward, part near orbital regions slightly convex; frontal margin lined with small, rounded granules, concave medially in dorsal view, divided into distinct two lobes; frontal region indistinct, only separated into obscure lobes by shallow grooves.

Supraorbital margins lined with small granules. Anterolateral margin not granulated, with 1 or 2 teeth behind external orbital tooth; external orbital tooth largest and most distinct, blunt, slightly sloping forward, first tooth indistinct, second tooth indistinct or absent. Posterolateral margins slightly convergent posteriorly; posterolateral regions regularly furnished with short, soft setae. Infraorbital ridge consisting of 16–21 small, rounded granules in both sexes.Surface of pterygostome with sparse soft setae. Epistome broad, median part triangular, margin with tiny granules.

Third maxillipeds ( Fig.2B View Figure 2 ) broad, external surface glabrous, exopod almost equal to ischium; mesial part of merus with oblique shallow groove, anterolateral angle broadly rounded, slightly sloping laterally; ischium without distinct vertical shallow groove on external surface.

Chelipeds ( Fig. 2D–F View Figure 2 ) symmetrical both in male and female, stronger in male. Merus without spines, dorsal margins with long soft setae, ventral margins glabrous. Surface of carpus glabrous, with several tiny granules, inner surface without obvious short setae, inner distal angle very blunt in male ( Fig. 2C View Figure 2 ); inner distal angle obtuse triangular and with 2–3tiny blunt teeth and a larger blunt spine in female. Outer surface of palm in male ( Fig. 2D View Figure 2 ) smooth, without distinct granules; inner surface glabrous, slightly convex medially. Movable finger approximately as long as palm, cutting edges with 3–5 small blunt teeth subdistally; immovable finger slightly shorter than movable finger, cutting edges with 2–3 smaller teeth and 1 large blunt tooth; proximal half of fingers with long dense soft setae, with single small pulvinus at base of fingers in male, both long dense soft setae and pulvinus absent in female. Female ( Fig. 2F View Figure 2 ) with outer surface of palm glabrous and granulated, inner surface glabrous, slightly convex medially; immovable finger with ridge consisting of small granules toward palm, fingers with sparse short setae at tips; movable finger slightly longer than palm.

Ambulatory legs ( Figs. 1 View Figure 1 , 2G, H View Figure 2 ) slender, P3 and P4 longest. Meri without spines, with long soft setae on proximal half of anterior margin, proximal part of posterior margins with sparse short setae.Carpi in P2– P5 without setae on anterior and posterior margins, anterior margins of distal part distinctly compressed. Propodus as long as dactylus in P2–P4 ( Figs. 1 View Figure 1 , 2G View Figure 2 ), propodus about 1.2 times length of dactylus in P5 ( Fig.2H View Figure 2 ), anterior margins of propodus and dactylus without setae, posterior margins of propodus sparsely setose, ventral surfaces of carpus and propodus almost glabrous. P4 ( Fig.2G View Figure 2 ) relatively long, anterior margins of propodus glabrous, posterior margins with sparse short setae. P5 ( Fig. 2H View Figure 2 ) relatively short, anterior margins of propodus glabrous, posterior margins of distal part of propodus with tuft of short setae.

Male pleon ( Fig. 2I View Figure 2 ) narrow, surface smooth, without any granules, lateral margins lined with short setae;telson tongue-shaped, slightly longer than sixth segment, distal margin of telson not concave, without tuft of setae.

Male G1 ( Fig. 2J–O View Figure 2 ) slender, almost straight, distally curved outwards, tip chtinous, with two short semicircle-shaped lobes in lateral view ( Fig. 2L, M View Figure 2 ), opened laterally and mesially, respectively; G2 shorter than 1/4 length of G1.

Coloration. Carapace and chelipeds varied from orange, yellowish-brown, deep wine to dark purple, with light brown or white spots on carapace; ventral surface of carapace and cheliped palm lighter than dorsal surface, usually light brown to white. Ambulatory legs white to light brown, with light brown spots or bands. Setae on cheliped palm light brown; setae on ambulatory legs dark brown to black.

Habitat. This species inhabits the intertidal area, with sediment composed of coral sand and pebbles. Individuals always hide under pebbles and were sometimes sympatric with Ptychognathus aff. barbatus , P.hachijoensis , and Pseudograpsus albus Stimpson, 1858 in Dingtanzih, Kenting, southern Taiwan.

Etymology. This species is named for the Japanese carcinologist Tune Sakai, who studied the crab fauna from Taiwan (e.g., Sakai, 1939) and described two new species of Ptychognathus from Taiwan ( P. ishii from Lanyu Island; P. takahasii from Danshuei).

Size. Largest male 6.7 × 5.5 mm (holotype, NCHUZOOL 17047); largest female (ovigerous) 5.9 × 5.2 mm (NCHUZOOL 16503).

Distribution. Only known from Kenting, southern Taiwan.

Remarks. This new species is similar to P. hachijoensis , P.insolitus , Ptychognathus pusillus Heller, 1865 , P. stimpsoni , and P. takahasii in the characters of anterolateral margin of carapace (with indistinct teeth behind external orbital tooth), but can be distinguished by the features of carapace, ambulatory legs and male G1s.

Ptychognathus sakaii View in CoL can be separated from P. hachijoensis View in CoL by 1) posterior margins of the dactylus and propodus of ambulatory legs only sparsely setose (vs. with obvious dense setae on posterior margins of dactylus and propodus); 2) anterior margins of distal part of carpus distinctly compressed (vs. anterior margins of carpus are not distinctly compressed) ( Figs. 2G, H View Figure 2 , 3A View Figure 3 ; Sakai, 1976: text-fig. 349c; Fukui, 1989: figs. 15, 16; Osawa and Ng, 2006: fig. 2F); 3) part near tip of G1 straighter, only slightly curved outwards (vs. part near tip of G1 distinctly curved).

Ptychognathus sakaii View in CoL can be separated from P. insolitus View in CoL by 1) carapace subquadrate, with 1 or 2 teeth behind external orbital tooth on anterolateral margin (vs. carapace relatively broader, with only 1 indistinct tooth behind external orbital tooth on anterolateral margin, sometimes this tooth absent) ( Figs. 2A View Figure 2 , 3B View Figure 3 ; Osawa and Ng, 2006: figs. 1, 2A; Li, 2015: fig. 1E); 2) ambulatory legs comparatively broad and short, with short setae only on posterior margins of dactylus and propodus (vs. ambulatory legs comparatively slender, with long setae on anterior and posterior margins of dactylus and propodus) ( Figs. 2G, H View Figure 2 , 3B View Figure 3 ; Osawa and Ng, 2006: figs. 1, 4A–D); 3) G1s slender, almost straight, chitinous structures on tip comparatively slender (vs. G1s stout and slightly curved, chitinous structures stout) ( Fig. 2J–O View Figure 2 ; Osawa and Ng, 2006: fig. 3E–G; Li, 2015: fig. 4B).

Ptychognathus sakaii View in CoL can be separated from P.pusillus View in CoL by 1) frontal region indistinct and separated into two obscure lobes by shallow grooves, lobes broader (vs. frontal region distinct and separated into two obvious lobes, lobes are narrower) ( Fig. 2A View Figure 2 ; De Man, 1905: 539, pl. 17(1–2)); 2) anterior margins of distal part of carpus of ambulatory legs distinctly compressed (vs. anterior margins not obviously compressed) ( Fig. 2G, H View Figure 2 ; De Man, 1905: 539, pl. 17(1)).

Ptychognathus sakaii View in CoL can be separated from P. stimpsoni View in CoL by 1) frontal margin concave, divided into two obvious lobes (vs. frontal margin only slightly concave, weakly divided into two indistinct lobes) ( Figs. 2A View Figure 2 , 3C View Figure 3 ; Hsu and Shih, 2020: figs. 2C, E, 4A); 2) anterior margins of distal part of carpus of ambulatory legs distinctly compressed, anterior margins of carpus and propodus almost glabrous (vs. anterior margins of distal part of carpus not compressed, anterior margins of carpus and propodus covered with dense short setae) ( Figs. 2G, H View Figure 2 , 3C View Figure 3 ; Hsu and Shih, 2020: figs. 2C, E, 4G, H).

Ptychognathus sakaii View in CoL can be separated from P. takahasii View in CoL by 1) frontal region of carapace divided into two obvious lobes, with 1 or 2 teeth behind external orbital tooth on each anterolateral margin, posterolateral margins only slightly convergent posteriorly (vs. frontal region weakly divided two lobes, with 3 teeth behind small external orbital tooth on each anterolateral margin, posterolateral margins apparently convergent posteriorly) ( Figs. 2A View Figure 2 , 3D View Figure 3 ; Sakai, 1939: text-fig. 115); 2) anterior margins of carpus of ambulatory legs distinctly compressed (vs. anterior margins of carpus of ambulatory legs not significantly compressed) ( Figs. 2G, H View Figure 2 , 3D View Figure 3 ; Sakai, 1939: text-fig. 115); 3) G1s slender in P. sakaii View in CoL (vs. stout in P. takahasii View in CoL ).