Gothus, Yuan & Jiang & Sha, 2024

Yuan, Zi-Ming, Jiang, Wei & Sha, Zhong-Li, 2024, Morphological and molecular evidence for Gothus teemo gen. et sp. nov., a new xanthid crab (Crustacea, Brachyura, Xanthoidea) from coral reefs in the South China Sea, with a review of the taxonomy of Actaeodes consobrinus (A. Milne-Edwards, 1867), Zoosystematics and Evolution 100 (3), pp. 965-987 : 965-987

publication ID	https://doi.org/ 10.3897/zse.100.117859
publication LSID	lsid:zoobank.org:pub:15CA9ED4-C24C-4AD7-81AC-F699FA953FE8
DOI	https://doi.org/10.5281/zenodo.12702516
persistent identifier	https://treatment.plazi.org/id/240FAE30-235A-49A8-995D-6209A7F68991
taxon LSID	lsid:zoobank.org:act:240FAE30-235A-49A8-995D-6209A7F68991
treatment provided by	Zoosystematics and Evolution by Pensoft
scientific name	Gothus
status	gen. nov.

Treatment

Gothus gen. nov.

Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5

Type species.

Gothus teemo sp. nov., by present designation.

Diagnosis.

Small species, CW under 10 mm. Carapace broader than long, dorsal surface bearing round granules, regions clearly defined; front wide, not protruding, divided into two slightly triangular lobes by a V-shaped notch; frontal lobes and dorsal inner orbital angle separated by shallow depression; eyestalks densely granulated; area beneath outer orbital angle slightly concave, not forming a subhepatic cavity; anterolateral margin with four teeth, first tooth flattened, sometimes completely reduced to appear as three teeth; posterolateral margin almost straight; subhepatic region densely granulated.

Epistome central region with low median projection on posterior margin. Maxilliped 3 granulated, anterior edge of merus indented, external terminal angle expanded. Antennule folding transversely; basal segment of antenna subrectangular; contacting ventral external frontal margin and ventral internal orbital angle; antennal flagellum filling orbital hiatus.

Chelipeds symmetrical, merus short; carpi robust, surface granulated, aggregated into nodules; outer and dorsal surfaces of palm densely granulated; fingers elongated, with triangular teeth; tips sharp, crossing at extremities when closed; dorsal surface of movable finger with three granulated ridges. Fingers brownish-black, coloration of immovable finger extending onto inner and outer surfaces of palm in male.

Ambulatory legs with meri flattened, granulated along anterior and posterior edges; dactyli elongated, margins with granules and setae, terminal end chitinous, sharp, slightly curved backward, dactylo-propodal lock present but underdeveloped.

Male thoracic sternum with sternites 1 and 2 completely fused, suture between sternites 2 and 3 straight, complete, sternites 3 and 4 mostly fused, suture between them visible only at margins, sternites 3 short, sternite 4 with central longitudinal groove, tubercle of sterno-pleonal lock located on posterior of sternite 5. Male pleon narrow, pleonites 3 to 5 completely fused, lateral margins of pleonite 6 slightly concave. Telson long, broad, truncated oval, base margin wider than terminal margin of pleonite 6.

G 1 slender, curving slightly outward, distal lobe spoon-shaped, long setae on inner subdistal part, small spines on outer part. G 2 not exceeding 1 / 6 length of G 1, distal lobe elongated.

Etymology.

The genus is named after the game of Go, alluding to the intermingled black and white patterns on the carapace, beneath which lie circular granules resembling the pieces of the game. “ - thus ” is a common suffix for species names within the Xanthidae family. Gender masculine.

Comparative material.

Rizalthus anconis Mendoza & PKL Ng, 2008 (Fig. 6 A View Figure 6 ). China • 1 female; CW 4.2 mm, CL 2.7 mm; Meiji Reef , Nansha Islands; 9 ° 52 ' 38.19 " N, 115 ° 31 ' 17.08 " E; 8 m; 7 May 2022; Ziming Yuan, Yuli Sun, Shaobo Ma coll.; NS-MJ- 2022-1457 GoogleMaps .

Hypocolpus haanii Rathbun, 1909 (Fig. 6 B View Figure 6 ). China • 1 male; CW 45.3 mm, CL 34.2 mm; Lingao Cape, Hainan Island ; 15–30 m; 20 Aug. 2018; Yunhao Pan coll.; MBM 286755 View Materials .

Euxanthus exsculptus (Herbst, 1790) (Fig. 6 C View Figure 6 ). China • 1 male; Wenchang, Hainan Island ; 20 Dec. 2018; Yunhao Pan coll.; Xan 016 • 1 male; Yongxing Island, Xisha Islands ; 15–17 May 1957; MBM 163793 View Materials • 2 males; Wood Island, Xisha Islands ; 1957; MBM 163791 View Materials • 1 male, 2 females; Wood Island, Xisha Islands ; 15–17 May 1957; MBM 163788 View Materials • 3 males, 3 females; East Island, Xisha Islands ; 28–31 May 1980; MBM 163785 View Materials • 1 female; Yongxing Island, Xisha Islands ; 11–13 Jun. 1980; MBM 163784 View Materials • 1 female; East Island, Xisha Islands ; 12 Jun. 1975; Xianqiu Ren coll.; MBM 163792 View Materials . CW 15–52.8 mm, CL 9.7–33.2 mm .

Euxanthus huonii (Hombron & Jacquinot, 1846) (Fig. 6 D View Figure 6 ). China • 1 male; Dengqing Island , Xisha Islands; 11–17 Apr. 1958; MBM 163762 View Materials • 1 female; Tree Island , Xisha Islands; 1 May 1958; MBM 163761 View Materials • 1 female; Yongxing Island , Xisha Islands; 7 May 1980; MBM 163780 View Materials • 2 females; Drummond Island , Xisha Islands; 1980; MBM 163781 View Materials • 1 male; Meiji Reef , Nansha Islands; 9 ° 53 ' 30.84 " N, 115 ° 34 ' 22.05 " E; 10 m; 10 May 2022; Ziming Yuan, Yuli Sun, Shaobo Ma coll.; NS-MJ- 2022-1734 . CW 19.3–37.3 mm, CL 13.1–26.4 mm GoogleMaps .

Psaumis cavipes (Dana, 1852) (Fig. 6 E View Figure 6 ). China • 1 female ovigerous; Xisha Islands, Jinqing Island ; 10 Jul. 2019; azp 01 • 1 male, 3 females; Sanya Station Front, Hainan; 30 Apr. 2021; Zhang Xu coll.; aop 01 • 2 males; Xisha Islands, Yongle blue hole; 10 Jul. 2019; aop 02 • 1 female ovigerous; Xisha Islands, Yongle blue hole; 10 Jul. 2019; aop 03 • 1 male; Phoenix Island, Sanya , Hainan; Zhang Xu coll.; 2022010 • 1 juvenile; Xisha Islands, Yuzhuo Reef ; 9 Jul. 2019; aop 04 • 2 males; Hainan, subtidal 9–10 m; 21 Nov. 2016; Xan 020-2. CW 5.1–17.4 mm, CL 3.3–10.6 mm

Remarks.

Gothus gen. nov. exhibits the closest resemblance to the subfamily Euxanthinae , particularly to Eux 1, as defined and morphologically summarized in the molecular systematic study by Lai et al. (2011)., mainly considering its anterolateral margin of the carapace, which does not clearly meet the orbit but instead continues down to the subhepatic region, presenting an ambiguous starting point (Fig. 1 B View Figure 1 ). Other characteristics justifying its inclusion are chelipeds almost completely symmetrical, which can be coapted against the carapace (Fig. 1 A View Figure 1 ); male pleon long, with the telson reaching to the level above the coxo-sternal condyles of pereiopod 1, and base of somite 3 only slightly wider than tip of somite 5 (Figs 2 F View Figure 2 , 3 F View Figure 3 ) (see also Serène, 1984; Lai et al. 2011). However, its ambulatory legs do not form a similar perfect coapted structure, especially since the corresponding posterolateral margin is nearly non-concave (Fig. 1 A, C View Figure 1 ). Other features notably distinguishing it from any member of the subfamily Euxanthinae are its extremely narrow male pleon with a long and broad, overall truncated oval telson (Figs 2 F View Figure 2 , 3 F View Figure 3 ), the base of which is wider than the width of the end of the sixth pleonite, the terminal end wide and rounded, with the lateral edges barely converging inward but rather forming two opposing arcs, unlike the typically triangular telson common in the Euxanthinae .

Gothus gen. nov. shares the closest similarities with the genus Rizalthus Mendoza & PKL Ng, 2008 , due to both possessing a granule-covered carapace surface, similar carapace outlines and front, developed cheliped carpus, and analogous G 1 structures. However, Gothus can be easily distinguished from Rizalthus by several key characteristics: its anterolateral margin with four teeth, first tooth flattened, sometimes completely reduced to appear as three teeth (Figs 1 A, C View Figure 1 , 3 A View Figure 3 ) (vs. no clearly defined teeth in Rizalthus ; Fig. 6 A View Figure 6 ; cf. Mendoza and Ng 2008: fig. 1 A); absence of etched depressions on body (Fig. 1 A View Figure 1 ) (vs. distinct etched depressions on thoracic sternum in Rizalthus ; cf. Mendoza and Ng 2008: fig. 1 C); central part of epistome raised (Fig. 1 B View Figure 1 ) (vs. central part of epistome not protruding in Rizalthus ; cf. Mendoza and Ng 2008: fig. 1 B); robust cheliped carpus, sometimes slightly expanded (Fig. 1 A View Figure 1 ) (vs. strongly expanded and protruding in Rizalthus ; Fig. 5 A View Figure 5 ; cf. Mendoza and Ng 2008: fig. 1 A); male pleon with a long, broad, truncated oval telson (Figs 2 F View Figure 2 , 3 F View Figure 3 ) (vs. a smaller, triangular telson in Rizalthus ; cf. Mendoza and Ng 2008: fig. 2 C); G 1 distal lobe curved inwards (Fig. 3 G – J View Figure 3 ) (vs. nearly straight, not curved inwards in Rizalthus ; cf. Mendoza and Ng 2008: fig. 2 F – H) and G 2 with a longer, straighter distal lobe (Fig. 3 K, L View Figure 3 ) (vs. shorter and curved in Rizalthus ; cf. Mendoza and Ng 2008: fig. 2 I).

Due to its similar carapace outline, particularly the less concave posterolateral margins, Gothus also resembles Visayax Mendoza & Ng, 2008 . However, it can be easily differentiated by the following characteristics: Gothus lacks erosive depressions across body (Fig. 1 A View Figure 1 ) (vs. chelipeds, ambulatory legs, carapace, and thoracic sternum with erosive depressions in Visayax ; cf. Mendoza and Ng 2008: figs 3–6); carapace regions more flattened (Fig. 1 A, C View Figure 1 ) (vs. carapace regions more pronounced in Visayax ; cf. Mendoza and Ng 2008: figs 3 A, C, 5 A, C); posterior three teeth on anterolateral margin of carapace well-developed (Fig. 1 A, C View Figure 1 , 3 A View Figure 3 ) (vs. absence of developed teeth on anterolateral margin in Visayax ; cf. Mendoza and Ng 2008: figs 3 A, 5 A); male abdominal telson larger, truncated oval (Figs 2 F View Figure 2 , 3 F View Figure 3 ) (vs. smaller, semi-circular in Visayax ; cf. Mendoza and Ng 2008: figs 4 E, 6 D); G 1 more slender (Fig. 3 G – J View Figure 3 ) (vs. G 1 more robust in Visayax ; cf. Mendoza and Ng 2008: figs 4 F, G, 6 F, G).

The new genus exhibits a general morphological similarity to typical Euxanthinae members such as Euxanthus Dana, 1851 , and Hypocolpus Rathbun, 1897 . In addition to the existing comparative specimens, Guinot-Dumortier (1960) provided excellent descriptions and photographs of species from the above two genera. Subsequently published species also have relatively clear morphological descriptions and images available for comparison (cf. Guinot 1971 b; Galil and Vannini 1990; Crosnier 1996). The new genus can be easily distinguished from Euxanthu s by the following features: entire body covered with granules and short pubescence (Fig. 1 A View Figure 1 ) (vs. relatively smooth in Euxanthus ; Fig. 6 C, D View Figure 6 ; cf. Guinot-Dumortier 1960: pl. VIII, figs 42, 44, 46, pl. IX, figs 48–52); carapace anterolateral margin with four teeth, first tooth flattened, sometimes completely reduced to appear as three teeth (Figs 1 A, C View Figure 1 , 3 A View Figure 3 ) (vs. 4–6 teeth on anterolateral margin in Euxanthus ; Fig. 6 C, D View Figure 6 ; cf. Guinot-Dumortier 1960: pl. VIII, figs 42, 44, 46, pl. IX, figs 48–52); front not prominent, divided by a V-shaped notch (Figs 1 C View Figure 1 , 3 A View Figure 3 ) (vs. more protruding, divided by a narrow fissure in Euxanthus ; Fig. 6 C, D View Figure 6 ; cf. Guinot-Dumortier 1960: pl. VIII, figs 42, 44, 46, pl. IX, figs 48–52); male abdominal telson large and truncated oval (Figs 2 F View Figure 2 , 3 F View Figure 3 ) (vs. small and triangular in Euxanthus ; cf. Guinot-Dumortier 1960: pl. VIII, fig. 47); G 1 with a prominent, spoon-shaped distal lobe, and long setae on inner subdistal part (Fig. 3 G – J View Figure 3 ) (vs. G 1 with a short, non-protruding distal lobe, inwardly curved and encircling, with short setae on inner subdistal part in Euxanthus ; cf. Guinot-Dumortier 1960: pl. VI, figs 36–39). Similarly, the new genus is easily distinguishable from Hypocolpus by the absence of a developed subhepatic cavity (Fig. 1 B View Figure 1 ) (vs. a developed subhepatic cavity in Hypocolpus ; cf. Guinot-Dumortier 1960: pl. II, figs 40–41); posterior three teeth on anterolateral margin well-developed (Figs 1 C View Figure 1 , 3 A View Figure 3 ) (vs. underdeveloped teeth in Hypocolpus ; Fig. 6 B View Figure 6 ; cf. Guinot-Dumortier 1960: pl. VII, figs 40–41); front not prominent, divided by a V-shaped notch (Figs 1 C View Figure 1 , 3 A View Figure 3 ) (vs. more protruding, divided by a narrow fissure in Hypocolpus ; Fig. 6 B View Figure 6 ; cf. Guinot-Dumortier 1960: pl. VII, figs 40–41); male abdominal telson large and truncated oval (Figs 2 F View Figure 2 , 3 F View Figure 3 ) (vs. small and triangular in Hypocolpus ; cf. Guinot-Dumortier 1960: pl. IX, fig. 53, pl. X, fig. 55); G 1 with a prominent, spoon-shaped distal lobe (Fig. 3 G – J View Figure 3 ) (vs. G 1 with a short, non-protruding distal lobe, inwardly curved and encircling in Hypocolpus ; cf. Guinot-Dumortier 1960: pl. VI, figs 32–35).

The new genus slightly resembles Psaumis Kossmann, 1877 , and Paractaeopsis Serène, 1984 , but can be readily distinguished. Gothus can be easily distinguished from Psaumis by lack of erosive depressions across body (Fig. 1 A View Figure 1 ) (vs. chelipeds, ambulatory legs, carapace with strong erosive depressions in Psaumis ; Fig. 6 E View Figure 6 ; cf. Serène 1984: pl. XVIII, fig. E); front divided by a V-shaped notch (Figs 1 C View Figure 1 , 3 A View Figure 3 ) (front divided by a narrow fissure in Psaumis ; Fig. 6 E View Figure 6 ; cf. Serène 1984: pl. XVIII, fig. E); anterolateral margin with four teeth, first tooth flattened, sometimes completely reduced to appear as three teeth (Figs 1 A, C View Figure 1 , 3 A View Figure 3 ) (anterolateral margin with very flat teeth, except for fourth tooth at junction of anterior and posterior lateral margins, which is more prominent in Psaumis ; Fig. 6 E View Figure 6 ; cf. Serène 1984: pl. XVIII, fig. E). It can be distinguished from Paractaeopsis by anterolateral margin with four teeth, first tooth flattened, sometimes completely reduced to appear as three teeth (Figs 1 A, C View Figure 1 , 3 A View Figure 3 ) (anterolateral margin with four well development teeth in Paractaeopsis ; cf. Takeda and Miyake 1968: fig. 1 a); carapace broad, approximately 1.5 times as wide as long, with a relatively flat dorsal surface (Figs 1 A, C View Figure 1 , 3 A View Figure 3 ) (carapace narrower, with a width not exceeding 1.4 times the length, and dorsal surface convex both anteroposteriorly and laterally in Paractaeopsis ; cf. Serène 1984: pl. XVII, fig. E); carapace 2 M region divided into two lobes (Figs 1 A, C View Figure 1 , 3 A View Figure 3 ) (carapace 2 M region divided into four lobes in Paractaeopsis ; cf. Takeda and Miyake 1968: fig. 1 a); ambulatory legs comparatively slender (Figs 1 A View Figure 1 , 3 D View Figure 3 ) (ambulatory legs very short and stout in Paractaeopsis ; cf. Takeda and Miyake 1968: fig. 1 c).

Given the above comparisons, the current species cannot be placed within any known genera, necessitating the establishment of a new genus. The main morphological characteristics comparing Gothus gen. nov. with closely related genera are listed in Table 2 View Table 2 .