Ptychognathus makii, Hsu & Shih, 2020

Hsu, Jhih-Wei & Shih, Hsi-Te, 2020, Romanogobio persus, Zoological Studies 59 (59), pp. 1-13 : 3-10

Family Varunidae H. Milne Edwards, 1853 Subfamily Varuninae H. Milne Edwards, 1853 Genus Ptychognathus Stimpson, 1858

Ptychognathus makii sp. nov. ( Figs. 2A, B , 3 ) urn:lsid:zoobank.org:act:0707FBBA-8465-477F-84C9-8A25053B45C6

Material examined: Holotype: 1 ò (23.5 mm), NCHUZOOL 16062, Jhonggang River (= R.) estuary, Manjhou, Pingtung, coll. P.-Y. Hsu et al., 7 Nov. 2018 . Paratype: 2 òò (13.2–13.6 mm), 1 ñ (11.2 mm), NCHUZOOL 16049, Gangkou R. estuary, Hengchun, Pingtung, coll. P.-Y. Hsu and C.-Y. Chi, 4 Dec. 2016; 1 ò (20.3 mm), NCHUZOOL 16050, Gangkou R. estuary, Hengchun, Pingtung, coll. P.-Y. Hsu et al., 4 Sep. 2017; 4 òò (12.8–21.0 mm), 1 ñ (16.3 mm), NCHUZOOL 16052, Gangkou R. estuary, Hengchun, Pingtung, coll. J.-J. Li, 19 Mar. 2018; 5 òò (7.9–19.8 mm), 3 ñ (6.6–10.6 mm), NCHUZOOL 16053, Gangkou R. estuary, Hengchun, Pingtung, coll. P.-Y. Hsu et al., 4 Sep. 2017.

Comparative material: Ptychognathus pilosus : 1 ò (20.2 mm), NCHUZOOL 15395, Gangkou R. estuary, Pingtung, coll. J.-J. Li, 10 Aug. 2015. P. altimanus : 2 òò (9.5–19.1 mm), NCHUZOOL 16055, Linbian R. estuary, Checheng, Pingtung, coll. J.-H. Lee, 6 Feb. 2000; 1 ò (17.4 mm), 1 ñ (19.7 mm), NCHUZOOL 16051, Gangkou R. estuary, Hengchun, Pingtung, coll. J.-J. Li, 10 Aug. 2015.

Description: Carapace ( Figs. 2A , 3A ) quadrate, slightly broader than long, 1.1 times as broad as long, flat; dorsal surface smooth, glabrous, regions weakly defined, with noticeable groove between epigastric regions. Front broad, flat, not sloping forward, part near orbital regions slightly convex; frontal margin straight, without lobes; postfrontal region indistinct, separated into two obscure lobes, without distinct shallow grooves. Anterolateral margins each with conspicuous three teeth including orbital tooth, first tooth largest and most distinct, third tooth smallest and most acute. Posterolateral margins divergent posteriorly, moderately sloping outwards; lateral and posterolateral margins regularly furnished with short, soft setae. Infraorbital ridge consisting of several small, rounded granules, decreasing in size laterally. Epistome broad, median part triangular, margin with tiny granules.

Third maxillipeds ( Figs. 2B , 3B ) broad, surface with short setae sparsely, exopod distinctly broader than ischium, exopod 1.7 times as broad as ischium; mesial part of merus with oblique groove, anteroexternal angle very broad, slightly sloping outwards; ischium with distinct vertical shallow groove.

Chelipeds ( Fig. 3D ) symmetrical in male. Merus without spines, margins lined with small, rounded granules, dorsal margins with long soft setae, ventral margins glabrous. Surface of carpus with several tiny granules, part near inner distal angle with single ridge consisting of large granules; inner surface sometimes with short setae sparsely; inner distal angle with single long blunt spine, slightly curving forward, and single smaller spine on margin in male ( Fig. 3C ); inner distal angle with single small spine in female. Outer surface of palm in male ( Fig. 3D ) smooth, without distinct granules; inner surface glabrous, middle part convex. Movable finger distinctly longer than palm; immovable finger with obscure horizontal ridge toward palm; cutting edges of both fingers with numerous blunt teeth, teeth near base of fingers larger; margins between movable finger and palm with short soft setae, without pulvinus at base of fingers. Female with outer surface of palm almost glabrous, inner surface glabrous and middle part convex; immovable finger with single prominent horizontal ridge toward palm; part near cutting edges with sparse short setae.

Ambulatory legs ( Fig. 3F, G ) slender, P3 and P4 longest, P4 and P5 obviously more flat than P2 and P3; anterior margins of each merus with long soft setae, posterior margins with short setae densely and long setae sparsely, with dense black short setae on margins near carpus; merus with single small spine on anterior margins near carpus in P2–P4, spine indistinct or absent in P5; propodus of P2–P4 narrower, propodus of P5 wider. Carpus and propodus of P2 covered with dense short setae on anterior margins, posterior margins of carpus without dense short setae, with dense black short setae on posterior margins of propodus, ventral surfaces of carpus and propodus with rows of short setae. P3 with anterior margins of propodus and carpus covered with dense short setae, ventral surface of propodus with rows of short setae, posterior margins of carpus without dense short setae, posterior margins of propodus with dense short setae and sparse long setae. P4 ( Fig. 3F ) shorter; carpus with anterior margins covered with dense short setae, posterior margins often glabrous; propodus two times as wide as long, anterior margins covered with dense short setae, posterior margins with dense long setae, denser on distal part. P5 ( Fig. 3G ) relatively shortest, anterior margins of carpus covered with dense short setae (denser on distal part); propodus oval, width as 1.5 times as length, anterior margins covered with dense short setae, posterior margins with dense long setae, denser on distal part.

Male pleon ( Fig. 3E ) narrow, surface smooth, without any granules, margins covered with short setae, setae on margins of telson longer; telson tongue-shaped, approximately as 1.2 times long as sixth segment, distal margin of telson not concave, without tuft of setae.

Male G1 ( Fig. 3H–K ) slender, slightly curving dorsally; tip blunt, with short chitinous structure, semicircle-shaped lobes in lateral view ( Fig. 3J, K ), opened laterally and dorsally; G2 shorter than 1/4 length of G1.

Coloration: Preserved specimens with carapace and ambulatory legs gray, brown or dark brown; ventral surface of carapace and chelipedal palm light brown; setae dark brown or black.

Habitat: This species inhabits estuarine areas with sandy mud sediment. Individuals always hid under stones or objects and were sometimes sympatric with P. altimanus and Varuna litterata in southern Taiwan.

Etymology: This species is named for the Japanese zoologist Moichiro Maki, who published the first monograph of Taiwanese decapods ( Maki and Tsuchiya 1923; Ng et al. 2009), which was also the first record of Ptychognathus in Taiwan.

Distribution: Southern Taiwan.

Size: Large; largest male CW 23.5 mm, largest female CW 16.3 mm.

Remarks: Among the species of Ptychognathus from Taiwan, this species is similar to P. altimanus (Rathbun, 1914) and P. pilosus De Man, 1892 in morphology, but can be distinguished by the characters of its frontal region, supraorbital margins, posterolateral margins of carapace, male chelipedal palms and G1s. Ptychognathus makii differs from P. altimanus by having a shorter frontal region with lateral margins not vertical (vs. longer with lateral margins vertical), supraorbital margins gently sinuous (vs. margins strongly sinuous) ( Figs. 2A , 3A ; Tesch 1918: pl. 4(5a), Naruse et al. 2005: fig. 1A); posterolateral margins of carapace distinctly divergent posteriorly (vs. almost parallel, not divergent posteriorly) ( Figs. 2A , 3A ; Tesch 1918: pl. 4(5a), Naruse et al. 2005: fig. 1A); male palms proximally almost smooth, without distinguishable granules (vs. with several tiny granules) ( Fig. 3D ; Naruse et al. 2005: fig. 1C), but the character is indistinct in smaller specimens; the margins of the chitinous structure of G1 without obvious notch (vs. with a notch) ( Fig. 3H–K ; Naruse et al. 2005: fig. 1E).

Ptychognathus makii and P. pilosus can be distinguished by the setae on chelipeds and G1. In P. makii , male and female with short soft setae on the margin between palm and movable finger ( Fig. 3D ), and cutting edge with sparse short setae in females. In P. pilosus , both male and female have a small tuft of shorter setae on tip of fixed finger, and longer setae on both fingers only in males (Li et al. 2019: fig. 7B). The tips of male G1 is blunt, and the chitinous structure is large semicircle-shaped in lateral view in P. makii (vs. tapering, and the chitinous structure is small pyramidshaped pyramid-liked in P. pilosus ) ( Fig. 3H–K ; Li et al. 2019: fig. 7C, D).

Ptychognathus stimpsoni sp. nov. ( Figs. 2C–F , 4 ) urn:lsid:zoobank.org:act:DF3F6955-235A-4588-A984-793595D6FDC0

Material examined: Holotype: 1 ò (7.9 mm), NCHUZOOL 16501, Wanlitong, Hengchun, Pingtung, Taiwan, coll. J.-W. Hsu, 15 Aug. 2016 . Paratype: 16 òò (7.3 - 10.9 mm), 4 ññ (7.5 - 8.8 mm), NCHUZOOL 16502, Camiguin, the Philippines, 31 Aug. 2003.

Comparative material: Ptychognathus aff. barbatus (see Remarks): 10 òò (7.7–12.4 mm), 5 ññ (8.9–13.9 mm), NCHUZOOL 16063, Dasi, Toucheng, Yilan, coll. J.-W. Hsu, 15 Aug. 2016; 2 òò (10.4–14.7 mm), 1 ñ (13.0 mm), 1 ñ (ovig.) (13.2 mm), NCHUZOOL 16064, Yanliao, Shoufeng, Hualien, coll. J.-W. Hsu, 29 June 2016; 2 ññ (6.7– 7.4 mm), NCHUZOOL 16065, Dulanwan, Donghe, Taitung, coll. P.-Y. Hsu et al., 9 Aug. 2017; 1 ò (13.0 mm), NCHUZOOL 16066, Shanyuan, Taitung, 27 July 2014; 2 òò (10.9–11.0 mm), 1 ñ (9.4 mm), NCHUZOOL 16067, Gihui, Chenggong, Taitung, coll. J.-W. Hsu, 28 Apr. 2017; 3 òò (12.1–14.9 mm), NCHUZOOL 16075, Fubao, Changhua, 16 Jan. 2017; 2 òò (18.9–20.2 mm), 1 ñ (11.5 mm), NCHUZOOL 16074, Gaoping R. estuary, Linyuan, Kaohsiung City, 29 Apr. 2009; 4 òò (9.9–16.9 mm), 1 ñ (8.6 mm), NCHUZOOL 16073, Houwan, Hengchun, Pingtung, 11 July 2017; 1 ò (13.0 mm), NCHUZOOL 16072, Baoli R. estuary, Checheng, Pingtung, 23 June 2014; 8 òò (9.3– 12.3 mm), 3 ññ (8.8 – 11.9 mm), 2 ññ (ovig.) (8.2–9.7 mm), NCHUZOOL 16070, Wanlitong, Hengchun, Pingtung, coll. J.-W. Hsu et al., 11 Dec. 2018; 5 òò (7.8–11.4 mm), 1 ñ (9.4 mm), NCHUZOOL 16071, Dingtanzih, Hengchun, Pingtung, coll. P.-Y. Hsu et al., 19 Mar. 2018; 3 òò (6.5–10.5 mm), 1 ñ (8.9 mm), NCHUZOOL 16069, Gangkou R. estuary, Hengchun, Pingtung, 18 Aug. 2016; 1 ò (14.7 mm), NCHUZOOL 16068, Jhonggang R. estuary, Manjhou, Pingtung, 7 Nov. 2018; 2 òò (6.3–12.3 mm), 1 ñ (10.8 mm), NCHUZOOL 16076, Watong, Baisha, Penghu, 2 Sep. 2014. Ptychognathus ishii Sakai, 1939: 3 òò (5.3–7.4 mm), 1 ñ (5.8 mm), NCHUZOOL 16033, Dasi, Toucheng, Yilan, coll. J.- W. Hsu, 15 Aug. 2016; 2 òò (8.9–11.4 mm), 2 ññ (8.9-9.1 mm), NCHUZOOL 16034, Dasi, Toucheng, Yilan, coll. J.-W. Hsu, 16 Aug. 2016; 1 ò (10.8 mm), NCHUZOOL 16035, Dulanwan, Donghe, Taitung, coll. P.-Y. Hsu, 29 June 2016; 1 ò (9.2 mm), 1 ñ (8.4 mm), NCHUZOOL 16036, Gangkou R. estuary, Hengchun, Pingtung, coll. J.-J. Li, 5 June 2015; 6 òò (11.0– 13.2 mm), 7 ññ (9.1-13.7 mm), NCHUZOOL 16037, Gangkou R. estuary, Hengchun, Pingtung, coll. J.-J. Li, 10 Aug. 2015; 1 ò (8.2 mm), 1 ñ (6.9 mm), NCHUZOOL 16038, Gangkou R. estuary, Hengchun, Pingtung, coll. J.-W. Hsu et al., 19 Mar. 2018; 1 ñ (ovig.) (10.27 mm), NCHUZOOL 16039, Gangkou R. estuary, Hengchun, Pingtung, coll. J.-W. Hsu et al., 18 Aug. 2016.

Description: Carapace ( Figs. 2 C – F , 4 A ) subquadrate, slightly broader than long, 1.2 times as broad as long, flat; dorsal surface smooth, glabrous, regions weakly defined, with noticeable groove between epigastric regions. Front broad, slightly sloping forward, part near orbital regions slightly convex; frontal margin slightly concave, weakly divided into indistinct two lobes; anterior margin lined with small, rounded granules, with row of small granules behind frontal margin, granulated ridge contiguous to anterior margin in lateral part, separated from anterior margin in middle part; postfrontal region indistinct, separated into obscure 2 lobes by shallow grooves. Anterolateral margins and supraorbital margins lined with small granules, anterolateral margin with three teeth including orbital tooth, first tooth most distinct and acute, slightly sloping forward; second and third teeth 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 ( Fig. 4B ) consisting of 12– 15 small, rounded granules. Surface of pterygostome with sparse soft setae. Epistome broad, median part triangular, margin with tiny granules.

Third maxillipeds ( Figs. 2D, F , 4C ) broad, surface with short setae sparsely, exopod slightly broader than or equal to ischium; mesial part of merus with oblique groove, anteroexternal angle broad, slightly sloping outwards; ischium with obscure vertical shallow groove.

Chelipeds ( Fig. 4E ) symmetrical in male. Merus without spines, dorsal margins with long soft setae, ventral margins glabrous. Surface of carpus smooth, without distinct granules, inner surface sometimes with short setae sparsely, inner distal angle blunt or obtuse triangular in male ( Fig. 4D ); inner distal angle with single spines in female. Outer surface of palm in male ( Fig. 4E ) smooth, without distinct granules or horizontal ridge; inner surface glabrous, middle part convex. Movable finger approximately as long as palm, inner surface glabrous and middle part convex; cutting edges of both fingers with numerous small blunt teeth, immovable finger with 2–3 larger blunt teeth; proximal half of fingers with long dense soft setae in male (absent in female), margin between movable finger and palm with short soft setae, with single small pulvinus at base of fingers. Female with outer surface of palm glabrous and granulated, inner surface glabrous, middle part convex; immovable finger with ridge consisting of large granules toward palm, fingers with sparse short setae at tips; movable finger slightly longer than palm.

Ambulatory legs ( Fig. 4G, H ) slender, P3 and P4 longest; mesial half of anterior margins of each merus with long soft setae, without spines, posterior margins without setae; propodus as long as dactylus in P2–P4 ( Fig. 4G ), propodus about 2 times length of dactylus in P5 ( Fig. 4H ). Carpi of P2 and P3 with dense short setae on anterior margins of distal half, anterior margins of propodus and dactylus all covered with dense short setae, posterior margins of propodus sparsely setose, ventral surfaces of carpus and propodus with rows of short setae. Carpi of P4 and P5 with dense short setae on anterior margins of distal 1/3–1/4, posterior margins of carpus glabrous. P4 ( Fig. 4G ) relatively long, anterior margins of propodus covered with dense short setae, posterior margins with sparse long setae; posterior margins of distal 1/2–1/3 propodus covered with dense short setae, ventral surface with rows of long setae sparsely. P5 ( Fig. 4H ) relatively short, anterior margins of propodus covered with dense short setae (denser on distal part), posterior margins of distal 1/3 propodus covered with dense short setae.

Male pleon ( Fig. 4F ) narrow, surface smooth, without any granules, lateral margins covered with short setae; telson tongue-shaped, approximately as long as sixth segment, distal margin of telson not concave, without tuft of setae.

Male G1 ( Fig. 4I–N ) slender, almost straight, part near tip more slender and slightly curving outwards; tip with short chitinous structure, two semicircle-shaped lobes in lateral view ( Fig. 4K, L ), opened laterally and mesially, respectively; G2 shorter than 1/4 length of G1.

Coloration: Preserved specimens with carapace gray to dark brown, ventral body white; chelipeds and ambulatory legs light gray to light brown, with setae brown.

Habitat: This species inhabits the intertidal area, with sediment composed of coarse sand. Individuals always hid under gravel and were sometimes sympatric with P. aff. barbatus in Wanlitong, Kenting, southern Taiwan.

Etymology: This species is named for the American zoologist William Stimpson, who established the genus Ptychognathus ( Stimpson 1858 1907).

Distribution: Southern Taiwan; the southern Philippines (Camiguin).

Size: Small, largest male CW 10.9 mm, largest female CW 8.8 mm, smallest ovigerous female 7.9 mm.

Remarks: This species can be distinguished from other congeners from Taiwan by a suite of characters of the frontal region, anterolateral margins of carapace, male cheliped, setae on ambulatory legs and male telson.

This new species is very similar to the East Asian “ Ptychognathus barbatus (A. Milne-Edwards, 1873) ” in morphology (see below); however, the identification of P. barbatus is problematic. In East Asia, Maki and Tsuchiya (1923) was the first report to identify Taiwanese specimens as “ P. barbatus ,” which was followed by subsequent studies of the East Asian species (e.g., Sakai 1939 1976; Dai et al. 1986; Dai and Yang 1991; Ng et al. 2001 2017). The type locality of P. barbatus is New Caledonia, and only a very brief description with dorsal view illustration was provided (A. Milne-Edwards 1873: 136, pl. 17(4)), without a detailed description of the ambulatory legs and male telson. Even so, it is clear that the frontal region is divided into two lobes by a shallow groove, with the posterolateral margins of carapace distinctly divergent posteriorly, and the propodus and dactylus of forth ambulatory legs are relatively slender. However, for the specimens from East Asia, the frontal region is slightly divided into obscure four lobes, with the posterolateral margins of carapace only slightly divergent posteriorly, and the propodus and dactylus of forth ambulatory legs are relatively short ( Sakai 1976: text-fig. 348, pl. 219(2); Dai and Yang 1991: pl. 65(8); Fukui et al. 1989: fig. 14). Further detailed morphological studies and molecular analyses are necessary to clarify this issue (N.K. Ng, personal communication). As a result, we temporally treat the species from East Asia as P. aff. barbatus .

Ptychognathus stimpsoni sp. nov. is very closely allied to the East Asian P. aff. barbatus , but both can be distinguished by the frontal region, setae on ambulatory legs and telson of male. Ptychognathus stimpsoni has a row of small granules behind the frontal margin (vs. without distinct granules behind the frontal margin in P. aff. barbatus ) ( Fig. 4A ; Sakai 1976: pl. 219(2)); the anterior margins of ambulatory carpi and propodi covered with dense short setae (vs. anterior margins of ambulatory carpus glabrous, only distal part of anterior margins of propodus covered with dense short setae) ( Fig. 4G, H ; Sakai 1976: pl. 219(2)); and the distal margin of male telson not concave, without a tuft of soft setae (vs. distal margin of male telson concave, with a tuft of soft setae) ( Fig. 4F ; Dai et al. 1986: fig. 262(4), Dai and Yang 1991: fig. 262(4)). The females of two species can be separated by the setae on the ambulatory legs as males.

In addition, P. stimpsoni is also similar to P. pusillus in morphology, but can be separated by the characters of ambulatory legs. The carpus of ambulatory legs covered with dense short setae on anterior margins of distal part in P. stimpsoni ( Fig. 4G, H ) (vs. anterior margins of ambulatory carpus glabrous in P. pusillus (De Man 1895: 99, fig. 22, De Man 1905: 539, pl. 17(1–5)).

The new species is also similar to P. ishii because the surfaces of carpus and propodus of ambulatory legs are covered with dense short setae in both species. However, the two species can be clearly distinguished by the features of carapace and setae on male chelipedal palm. In P. stimpsoni , the dorsal surface of carapace almost glabrous, anterolateral margin with three teeth, only third tooth indistinct or notch (vs. carapace covered with short black setae, anterolateral margin with two or three teeth, third tooth indistinct or absent in P. ishii ( Fig. 4A ; Sakai 1976: 639, text-fig. 349a, pl. 219(3)); and the proximal half of both fingers with long dense soft setae in male (vs. fingers with a tuft of long setae on outer surface extending to base of palm, mostly expanding onto fixed finger in male P. ishii ( Fig. 4E ; Sakai 1976: 639, text-fig. 349b)).

Figures

Fig. 2. A–B: Ptychognathus makii sp. nov., holotype (male, CW 23.5 mm; NCHUZOOL 16062). C–F: Ptychognathus stimpsoni sp. nov.; C, D: holotype (male, CW 7.9 mm; NCHUZOOL 16501). E, F: paratype (male, CW 10.9 mm; NCHUZOOL 16502).

Fig. 3. Ptychognathus makii sp. nov., holotype (male, CW 23.5 mm; NCHUZOOL 16062). A, carapace; B, left third maxilliped; C, left carpus of cheliped (dorsal view); D, outer view of left cheliped; E, pleon; F, left third ambulatory leg; G, left forth ambulatory leg; H–I, right G1; H, I, dorsal view; J, K, lateral view.

Fig. 4. Ptychognathus stimpsoni sp. nov., holotype (male, CW 7.9 mm; NCHUZOOL 16501). A, carapace; B, left infraorbital ridge; C, left third maxilliped; D, left carpus of cheliped (dorsal view); E, outer view of left cheliped; F, pleon; G, left third ambulatory leg; H, left forth ambulatory leg; I–N, right G1; I, J, dorsal view; K, L, lateral view; M, N, ventral view).