Juxtaxanthias lividus

Juxtaxanthias lividus (Latreille, in Milbert, 1812)

[Jn: Murasaki-hime-ougigani]

(Fig. 2E)

Material examined. Chichi-jima Is. — Chichi-jima I., Futami Bay, 1 ♂ (NSMT-Cr 31527; cb 46.6×cl 31.0 mm), date unknown, Ogasawara Fisheries Center leg.

Remarks. Juxtaxanthias lividus (Latreille, in Milbert, 1812), one of three representatives of the genus Juxtaxanthias Ward, 1942, is close to J. tetraodon (Heller, 1861) in the general appearance of the carapace, chelipeds and ambulatory legs. Forest and Guinot (1961) extensively studied and distinguished these two species known as the Xanthias species, but did not approve of the generic validity of Juxtaxanthias. Sakai (1976) and Sèrene (1984) followed this synonymization in their monographic works, but the validity of Juxtaxanthias is at present generally accepted (Ng et al., 2008), with the three species attaining to much larger size than all the Xanthias species.

According to the precedent studies, the important characters to distinguish J. lividus from J. tetrodon is the proportional difference of the carapace (carapace broader, with breadth ca. 1.65 times length, in J. lividus; carapace narrower, with ca. 1.55, in J. tetraodon), and the difference of the first two anterolateral teeth (rounded lobular first tooth followed by the angular second tooth, in J. lividus; angular first lobe, with the pointed second tooth, in J. tetraodon). The present specimen is closer to J. tetraodon in the carapace proportion and the anterolateral teeth are also closer to J. tetraodon, but finally identified as J. lividus, agreeing well with the photograph given by Balss (1938, pl. 2 fig. 1) and the colored figure by Sakai (1976). These characters seem to be not always strong enough to distinguish the two species with individual and developmental variations.

Distribution. In Japanese waters, the known localities are Kagoshima Bay and Northern Daito-jima Island (Sakai, 1939, as Xanthias tetraodon), Yoron-to Island (Sakai, 1976, as Xanthias lividus). Nagai and Nomura (1988) published the colored photograph of a dried specimen from the Ryukyu Islands without exact locality. This species is otherwise known from Mauritius, the Chagos Islands, the Lakshadweep Islands and Sumatra in the Indian Ocean, and the Marshall Islands in the West Pacific (Forest and Guinot, 1961; Suvarna Devi et al., 2019).