Tetralia rubridactyla Garth, 1971

(Fig. 5A–L)

Tetralia glaberrima f. rubridactyla Patton, 1966: 287 [not available].

Tetralia glaberrima rubridactyla Garth, 1971: 185 .

Tetralia rubridactyla . —Galil 1988: 65, figs. 1d, 2g, h.— Castro 1997a: 70, pl. 1E; 1997b: 113; 1999a: 41; 1999b: 102; 2003: 442; 2009: 278.— Castro et al. 2004: 25 (list).—Castro & Titelius 2008: 322.— Ng et al. 2008: 185, fig. 138.— Limviriyakul et al. 2016: 4, fig. 4l (Taiwan Island).— Maenosono 2017: 43, fig. 9(the Ryukyus).

Tetralia innamorata Galil & Clark, 1988: 138, figs. 1B, 2A, 3B, 4B, G, 6B.

Material examined. Nansha Islands: Mischief Reef, 115°32.5’E 9°55.7’N, 11 m, coll. Shaobo Ma, Yuli Sun, Ziming Yuan, 5 May 2022, 1 female (7.31 × 6.48 mm), NS-MJJ-2022-1097; 1 male (6.98 × 6.20 mm), NS-MJJ-2022-1098; 115°29.8’E 9°54.4’N, 13 m, coll. Shaobo Ma, Yuli Sun, Ziming Yuan, 6 May 2022, 1male (6.07 × 5.57 mm), 1 female (6.75 × 6.15 mm), NS-MJJ-2022-1208; 115°31.3’E 9°52.6’N, coll. Shaobo Ma, Yuli Sun, Ziming Yuan, 8 m, 7 May 2022, 1male (7.56 × 7.11 mm), 1 female (8.31 × 7.32 mm), NS-MJJ-2022-1410; 115°33.6’E 9°53.0’N, 10 m, coll. Shaobo Ma, Yuli Sun, Ziming Yuan, 8 May 2022, 1 female (5.30 × 4.87 mm), 1 pre-adult (4.45 × 3.77 mm), NS-MJJ-2022-1517; 115° 34.4’E 9°53.5’N, 10 m, coll. Shaobo Ma, Yuli Sun, Ziming Yuan, 10 May 2022, 1 male (6.87 × 5.59 mm), NS-MJJ-2022-1731, in Acropora tenuis ( Acroporidae) ; 1 female (9.34 × 8.38 mm), NS-MJJ-2022-1735; 115°34.4’E 9°53.5’N, 8 m, coll. Shaobo Ma, Yuli Sun, Ziming Yuan, 11 May 2022, 1 male (6.62 × 6.14 mm), 1 female (7.07 × 6.21 mm), NS-MJJ-2022-1868; 2 pre-adults (4.02 × 3.22 mm; 4.15 × 3.40 mm), NS-MJJ-2022-1871; 1 female (6.70 × 6.11 mm), NS-MJJ-2022-1874. Fiery Cross Reef, 112°58.9’E 9°39.5’N, 3 m, coll. Shaobo Ma, Yuli Sun, Ziming Yuan, 13 May 2022, 1 male (5.54 × 5.21 mm), 1 female (6.01 × 5.45 mm), NS-YS-2022-1093. — Zhongsha Islands: Walker Shoal, 114°29.0’E 15°55.0’N, 15 m, coll. Shaobo Ma, Yuli Sun, Ziming Yuan, 17 May 2022, 1 male (7.74 × 7.39 mm), 1 female (8.17 × 7.49 mm), ZS-MB-2022-1030. — Xisha Islands: The Seven Connected Islets, 112°16.2’E 16°58.0’N, 10 m, coll. Shaobo Ma, Yuli Sun, Ziming Yuan, 19 May 2022, 1 female (7.29 × 6.57 mm), XS-QL-2022-1007 ; 1 male (4.72 × 4.38 mm), 1 female (4.36 × 3.75 mm), 3 juveniles (3.55 × 3.21 mm; 2.29 × 1.98 mm; 3.51 × 3.05 mm), XS-QL-2022-1020; 1 male (4.92 × 4.45 mm), 1 female (5.45 × 4.80 mm), XS-QL-2022-1047; 3 males (5.69 × 4.98 mm; 6.90 × 6.30 mm; 5.68 × 5.01 mm), 3 females (5.54 × 5.17 mm; 5.42 × 4.95 mm; -6.04 × 5.40 mm), XS-QL-2022-1048; 1 male (5.78 × 5.15 mm), 1 female (5.46 × 5.04 mm), XS-QL-2022-1063; 112°19.6’E 16°57.1’N, 10 m, coll. Shaobo Ma, Yuli Sun, Ziming Yuan, 21 May 2022, 1 male (5.22 × 4.55 mm), 1 female (5.45 × 4.80 mm), XS-QL-2022-1074; 1 female (5.82 × 5.21 mm), XS-QL-2022-1126, in partially dead Acropora ( Acroporidae) reef; 1 male (5.25 × 4.90 mm), 1 female (5.60 × 5.43 mm), XS-QL-2022-1138.— Hainan Island: Xiao Dong Hai, 2–3 m, coll. Lecheng Qu, 5 December 2021, 1 female (11.11 × 9.53 mm), SY23. Jia Jing Dao, coll. Dong Dong, 28 March 2018, 1 male (6.38 × 5.75 mm), JJD. Hou Hai, 2–3 m, coll. Yuli Sun, 25 July 2022, 1 female (5.03 × 4.45 mm), SY71. Found in Acropora sp. ( Acroporidae) unless otherwise noted .

Geographical distribution. Across Indo-West Pacific region except Hawaiian Islands (Castro et al. 2004).

Remarks. Tetralia rubridactyla is one of the most common coral symbionts in the South China Sea. We found several different color patterns from the specimens collected. The brown color pattern is the most common (Fig. 5A, B, NS-MJJ-2022-1868), another color pattern, with light brown or orange-brown carapace with purple frontal and anterolateral margins is also common (Fig. 5D, XS-QL-2022-1048; Fig. 5G, XS-QL-2022-1074). In another color pattern, the body is uniform fuchsia with a conspicuous orange-red finger distinct from the carapace color (Fig. 5C, NS-MJJ-2022-1735).An uncommon color pattern is the rainbow pattern, where the specimen exhibits a green-bluepurple iridescence on the frontal area when alive and retains this iridescence in alcohol-preserved specimens, and the background color of chelipeds is almost white (Fig. 5E, F, XS-QL-2022-1047). This phenotype has been recorded on some websites before ( Tetralia sp., Coral crab. Male. Dorsal view, http://decapoda.aquarius-s.ru/tetraliidae/tetr_ nigr_01en.html), and its adult size is the smallest of all color patterns (ovigerous female: CL 4.36 mm, CW 4.83 mm; male: CL 4.45 mm, CW 4.92 mm). In addition, a special color pattern was found on a tiny ovigerous female, which has a wide black band with clear edges followed the frontal and anterolateral margins of carapace, it also has yellow dactylus of all chelipeds and pereiopods (Fig. 5K, L, SY71), only the setae-filled depression on propodus and anterior margin of carpus of chelipeds are dark-brown showing it to be Te. rubridactyla . The juveniles and pre-adults have orange or yellow fingers of white chelipeds and black or brown band in the frontal and anterolateral margins of carapace (Fig. 5H–J, NS-MJJ-2022-1517, XS-QL-2022-1020). Specimens with different color patterns were found at the same location, thus the diversity of color patterns is independent of the region and is suspected to be related to the color of host coral. Even with such striking differences in body coloration, their COI genes show almost no variation. COI sequences differences among samples with different color patterns are shown in the phylogenetic tree (Fig. 11).