Thalamitoides tridens A. Milne-Edwards, 1869

Huang, Yu-Hsuan & Shih, Hsi-Te, 2021, Chthonius rhodochelatus Hadzi 1933, Zoological Studies 60 (60), pp. 1-45 : 26-28

Thalamitoides tridens A. Milne-Edwards, 1869 ( Figs. 4D , 16 )

Thalamitoides tridens A. Milne-Edwards, 1869: 149 , pl. 6(1–7) (type locality: Tulear, Madagascar); Stephenson and Rees 1967: 102, fig. 38 ( Samoa; Palau; Philippines); Sakai 1976: 382, pl. 134(2) ( Japan: Ryukyus); Chen 1980: 134, fig. 17, pl. 3(5) (Xisha Is.); Dai et al. 1986: 239, fig. 140B (Xisha Is.); Dai and Yang 1991: 259, fig. 140B (Xisha Is.); Yang et al. 2008: 791 (list; Xisha Is.); Yang et al. 2012: 343, fig. 136 (Xisha Is.); Sasaki 2019: 9278 (list).

Thalamitoides tridens tridens – Ng et al. 2008: 155 (list).

Thalamitoides cf. tridens – Shih et al. 2020b: 36 (Dongsha I.).

Material examined: Taiwan: 1 male (14.9 × 7.4 mm), 2 females (16.1 × 8.2 mm, 1 soft shell) (NCHUZOOL 16520), Dongsha I. (20°42'3.1"N 116°43'4.4"E), coll. YH Huang and CY Chi, 16 Aug. 2019; 4 males (9.1–11.6 × 5.0– 6.1 mm), 3 females (9.0– 10.9 × 4.7–5.7 mm) (NCHUZOOL 16521), Dongsha I. (20°42’18.6”N 116°43’43.5”E), coll. YH Huang and CY Chi, 18 Jun. 2019; 1 female (15.8 × 7.5 mm) (NCHUZOOL 16522), Dongsha I. (20°42'3.1"N 116°43'4.4"E), coll. YH Huang and CY Chi, 23 Sep. 2019; 1 male (11.2 × 5.9 mm), 3 females (7.9–11.8 × 4.2–6.2 mm) (NCHUZOOL 16523), Dongsha I.

A 5 mm

(20°42'18.6"N 116°43'43.5"E), coll. YH Huang et al., 15 Jun. 2019; 3 males (8.6–10.6 × 4.5–5.4 mm), 1 female (7.5 × 3.9 mm) (NCHUZOOL 16595), Dongsha I. (20°42'18.6"N 116°43'43.5"E), coll. YH Huang, 17 Jun. 2019.

Diagnosis: Carapace with surface smooth slightly convex, 1.9 times broader than long, broadest between anterolateral tooth 1. Frontal and mesogastric ridges unbroken; epibranchial regions with a pair of ridges; protogastric, metagastric, mesobranchial and cardiac ridges absent ( Fig. 16A ). Front with 4 lobes, median 2 lobes 2.5 times broader than lateral. Supraorbital margins with 2 notches, inner lobe slightly arched ( Fig. 16A ). Anterolateral margins with 3 teeth, decreasing in size posteriorly ( Fig. 16A ). Basal antennal segment with a row of granules ( Fig. 16B ). Chelipeds with surface smooth, merus with 4 spines on inner margin, distal end of ventral surface with a spinule near articulation of carpus; carpus with 5 sharp spines, palm with 2 rows of spines on dorsal surface, inner row with 4 spines, outer with 3 spines; finger tips spoon-shaped ( Fig. 16C ). P5 with merus having strong spine on inner margin, distal end with small spine; carpus with 1 spine on outer margin; inner margin of propodus with 8–10 spines; dactylus with spinules on distal margins. Male pleon with pleomere 6 trapezoidal. G1 stout, distal part with bristles on lateral side ( Fig. 16D–E ).

Coloration in life: Carapace, chelipeds and legs dark green ( Fig. 4D ).

Distribution: Hawaii; Samoa; Fiji; New Caledonia; Australia (eastern); Indonesia; Guam; Palau; Philippines; Taiwan (Dongsha I.; Fig. 1 : no. 17); Japan (Ryukyus); Xisha Is.; Gulf of Aden; Red Sea; Madagascar (Tulear); Mauritius ( Sasaki 2019; this study).

Ecological notes: This species can be found from the intertidal and shallow subtidal zones in rocky shore and coral reefs. The juveniles were found from the seagrass beds or under stones on intertidal flats with coral sand.

Remarks: Thalamitoides tridens A. Milne-Edwards, 1869 is similar to Tho. spinigera Nobili, 1905 in the character of 3 anterolateral teeth. The specimens from Taiwan agree with Tho. tridens in the following characters: (1) basal antennal segment with granules in Tho. tridens ( Fig. 16B; A . Milne-Edwards 1869: pl. 6(2)) (3–4 spines in Tho. spinigera; Nobili 1905: 403; Spiridonov and Neumann 2008: fig. 2B); (2) Tho. spinigera with lateral front lobes rounder than Tho. tridens ( Fig. 16A; A . Milne-Edwards 1869: pl. 6(1); Spiridonov and Neumann 2008: fig. 2A); (3) G1 tip enlarged in Tho. tridens ( Fig. 16D–E ; Yang et al. 2012: fig. 136d, e) (vs. not enlarged in Tho. spinigera; Spiridonov and Neumann 2008: fig. 2D, E).

Figures

Fig. 4. Species of the family Portunidae. A, Thalamita gatavakensis Nobili, 1906, male (16.5 × 9.3 mm) (NTOU), Mao-ao, New Taipei City; B, Thalamita spinifera Borradaile, 1902, female (12.6 × 9.0 mm) (NCHUZOOL 16531), Erzihliao Fishing Port, Kaohsiung; C, Thalamitoides quadridens A. Milne-Edwards, 1869, male (25.4 × 13.3 mm) (NTOU), Sansiantai, Taitung; D, Thalamitoides tridens A. Milne-Edwards, 1869, female (16.1 × 8.2 mm) (NCHUZOOL 16520), Dongsha I.; E, Thranita cerasma (Wee & Ng, 1995), female (66.4 × 42.6 mm) (NCHUZOOL 16537), Dongsha I.; F, Thranita coeruleipes (Hombron & Jacquinot, 1846), male (59.7 × 40.5 mm) (NCHUZOOL 16507), Wanlitong, Kenting, Pingtung.

Fig. 16. Thalamitoides tridens A. Milne-Edwards, 1869, male (14.9 × 7.4 mm). A, carapace; B, basal antennal segment; C, palm of left cheliped (outer view); D–E, right G1; D, dorsal view; E, ventral view.

Fig. 1. Taiwan main island and adjacent islets, with the collection localities shown in gray circles (see Table 1).