ABSTRACT
High-level classifications of Anomura typically recognize three major clades: Galatheoidea (squat lobsters and porcelain crabs), Paguroidea (hermit and king crabs), and Hippoidea (mole crabs). The general stability of this classification, however, has masked the vigorous debate over internal relationships. Phylogenetic relationships of the Anomura are analyzed based on sequences from three molecular loci (mitochondrial 16S; nuclear 18S and 28S), with multiple exemplars representing 16 of 17 extant families. The dataset assembled is the largest analyzed to date for Anomura. Analyses under maximum parsimony and Bayesian inference recognize a basal position for Hippoidea, corroborating several recent studies, but point to significant polyphyly in the two largest superfamilies, Galatheoidea and Paguroidea. Three independent carcinization events are identified (in Lithodidae, Porcellanidae, and Lomisidae). The polyphyletic origin of asymmetrical hermit crabs is a radical departure from previous studies and suggests independent derivations of asymmetry in three separate clades: Paguridae, Coenobitidae + Diogenidae, and Parapaguridae. Such a scenario may seem unlikely owing to the complex characters involved, but if carcinization has multiple, independent origins, then adaptation to dextral shell habitation may also be plausible. Polyphyly of Galatheoidea, however, while unexpected, is morphologically tenable-characters traditionally used to unify Galatheoidea are plesiomorphies. Chirostylid squat lobsters are more closely related to an assemblage including aegloids, lomisoids, and parapagurids than to other galatheoids. Galatheidae may be paraphyletic on the basis of an internally nested Porcellanidae, and a similar situation may obtain for Chirostylidae with respect to Kiwaidae. Present topologies are not sufficiently robust to justify significant changes to the classification, but they point to fruitful lines for further research.
