The first record of an Eastern Pacific invasive crab in Taiwanese waters: Amphithrax armatus (Saussure, 1853) (Brachyura: Majoidea: Mithracidae), with notes on the taxonomy of the genus.
The tropical Eastern Pacific mithracid spider crab Amphithrax armatus (Saussure, 1853), known thus far only from Mexico, Nicaragua, and Panama, is here reported for the first time from southern Taiwan in the Indo-West Pacific region. The invasive species probably entered via ballast water or as fouling fauna on large ships that ply the Pacific shipping routes. This is only the second record of an American majoid entering Asian seas, the first being the inachoidid Pyromaia tuberculata (Lockington, 1877) from the American Pacific to Japan. The genetic data, using three mitochondrial genes (12S rRNA, 16S rRNA and COI) and two nuclear genes (18S rRNA and H3), indicates that A. armatus does not belong to the genus AmphithraxWindsor & Felder, 2017, as currently defined, with the species genetically closer instead to taxa in NonalaWindsor & Felder, 2014 and AlaLockington, 1877. This is also supported by a number of morphological characters. Amphithrax thus needs to be revised.