A new species of Gaillardiellus Guinot, 1976 (Crustacea, Brachyura, Xanthidae) from the coral reefs of the South China Sea

A new xanthid species of <i>Gaillardiellus</i> Guinot, 1976, is described from the coral reefs of the Xisha and Nansha Islands in the South China Sea. The new species, <i>Gaillardiellusmagiruber</i> <b>sp. nov.</b>, closely resembles <i>G.rueppellii</i> (Krauss, 1843) but can be distinguished mainly by its closer proximity of the outer orbital angle and anterolateral margin, which lacks an accessory lobe, a broader and non-protruding front, and notable differences in live coloration and size. Molecular analysis of mitochondrial cytochrome <i>c</i> oxidase I (COI) sequences further corroborates the validity of this new species. An updated identification key for <i>Gaillardiellus</i> is provided.