Evolutionary relationships among American mud crabs (Crustacea: Decapoda: Brachyura: Xanthoidea) inferred from nuclear and mitochondrial markers, with comments on adult morphology

Abstract

Members of the brachyuran crab superfamily Xanthoidea sensu Ng, Guinot & Davie (2008) are a morphologically and ecologically diverse assemblage encompassing more than 780 nominal species. On the basis of morphology, Xanthoidea is presently regarded to represent three families: Xanthidae, Pseudorhombilidae, and Panopeidae. However, few studies have examined this superfamily using modern phylogenetic methods, despite the ecological and economic importance of this large, poorly understood group. In this study we examine phylogenetic relationships within the superfamily Xanthoidea using three mitochondrial markers, 12S rRNA, 16S rRNA, and cytochrome oxidase I (COI), and three nuclear markers, 18S rRNA, enolase (ENO) and histone H3 (H3). Bayesian and maximum-likelihood analyses indicate that the superfamily Xanthoidea is monophyletic; however, the families Xanthidae, Panopeidae, and Pseudorhombilidae, as defined by Ng et al., are not, and their representative memberships must be redefined. To this end, some relevant morphological characters are discussed.

A new genus and species of xanthoid crab (Decapoda: Brachyura) from offshore hard bank habitats in the Gulf of Mexico

“…The present study builds upon previous efforts to clarify species composition and evolutionary relationships of American xanthoid crabs (Thoma et al 2009(Thoma et al , 2014Felder & Thoma 2010;Thoma & Felder 2012;Lasley et al 2013). It augments previously reported molecular genetic inferences with morphological findings to justify a family assignment and provides taxonomic descriptions at the generic and species level.…”

“…Where shown, meters (m) indicate collection depths. GenBank accession numbers are as previously published by Thoma et al (2009Thoma et al ( , 2014, with the addition of equivalent USNM catalog numbers shown for the archived source specimens of extracted tissues.…”

“…Being one of several small, similarly shaped, sympatric xanthoid species in such habitats, all varying with maturity and poorly illustrated in taxonomic literature, it is not unexpected that an undescribed species could be overlooked. However, where previous reports are based upon archived materials, as in the case of Thoma et al 2009Thoma et al , 2014Felder & Thoma 2010;and Lai et al 2011, we herewith provided characters for correction of at least some previous misidentifications.…”

Phylogenetic relationships of the ubiquitous coral reef crab subfamily Chlorodiellinae (Decapoda, Brachyura, Xanthidae)

“…; Thoma et al . ). Cyclodius paumotensis is also a much smaller species than S. flava or S. melanospinis .…”

“…() and Thoma et al . () showed that many eastern American xanthid genera now classified in the Euxanthinae, Actaeinae and Zosiminae actually form natural groups and likewise for Ratha . This ‘east American clade’ will also require revision.…”