Allogalathea (Decapoda: Galatheidae): a monospecific genus of squat lobster?

Abstract

The genus Allogalathea was established by Baba in 1969 to include the well-known species Galathea elegans. This species is widely distributed across the Indo-West Pacific Ocean, and is characterized by living in close association with crinoids, and by its conspicuous coloration. Although the genus is considered monospecific, different colour patterns and discrete morphological variations mainly associated with the rostrum and chelipeds have been reported. These differences could point to cryptic species, thereby questioning Allogalathea as a monotypic taxon. To address this issue, we sequenced the mitochondrial cytochrome oxidase I (COI; 658 bp) and 16S rRNA (882 bp) genes and the nuclear gene phosphoenolpyruvate carboxykinase (PEPCK; 598 bp) in numerous specimens from eight different localities, and also examined their morphological characters. DNA sequences were analysed using maximum-parsimony, maximum-likelihood, and Bayesian approaches of phylogenetic inference. The resulting trees were combined with morphological evidence to test species boundaries. Our molecular data revealed four deeply divergent clades, which can be distinguished by subtle morphological differences in the spinulation and length : breadth ratio of the P1 carpus, spinulation of the walking legs, and shape of the rostrum. Our findings indicated that Allogalathea elegans is in fact a species complex comprising four different species, which, although genetically very distinct, are morphologically very similar. We provide morphological descriptions and a key to these four species of the genus.