Molecular phylogenetic analysis of the Paguristes tortugae Schmitt, 1933 complex and selected other Paguroidea (Crustacea: Decapoda: Anomura)

Phylogenetic synthesis of morphological and molecular data reveals insights on the classification of diogenid hermit crabs (Crustacea: Decapoda: Anomura)

The family Diogenidae Ortmann, 1892 is a diverse and abundance group of hermit crabs, but their systematics and phylogenetic relationships are highly complex and unresolved. Herein, we gathered nucleotide sequence data from two mitochondrial (16S rRNA and COI) and two nuclear (NaK and PEPCK) genes for a total of 2,308 bp in length across 38 species from six extant diogenid genera. Molecular data were combined with 41 morphological characters to estimate the largest phylogeny of diogenid hermit crabs to date with the aim of testing the proposed taxonomic scheme of Diogenidae and addressing intergeneric relationships within this family. Despite conflicts between mitochondrial and nuclear DNA trees, the combined-data tree reflects the contributions of each dataset, and improves tree resolution and support for internal nodes. Contrary to traditional classification, our total evidence revealed a paraphyletic Diogenidae based on internally nested representatives of Coenobitidae Dana, 1851. Within Diogenidae, the studied diogenid hermit crabs were split between two clades with high support, which contradicts recent morphological classification scheme for Diogenidae sensu lato based on fossil records. The genus Diogenes Dana, 1851 was found nested inside Paguristes Dana, 1851, which formed a clade being separated from the remainder, pointing towards paraphyly in Paguristes. In another clade, Dardanus Paulson, 1875 occupied a basal position relative to the other diogenids, while Calcinus Dana, 1851 and Clibanarius Dana, 1852 showed sister relationships and formed a cluster with Ciliopagurus Forest, 1995. Among the morphological characters examined, carapace shield and telson were identified as phylogenetically significant for grouping diogenid genera, while phylogenetic insignificance of gill number was evidenced by its mosaic pattern in diogenid phylogeny. The present study sheds light on the controversial generic phylogeny of Diogenidae and highlights the necessity for thorough taxonomic revisions of this family as well as some genera (e.g., Paguristes) to reconcile current classifications with phylogenetic relationships.

A new species of the diogenid hermit crab genus Pseudopaguristes McLaughlin, 2002 from the Northern Mariana Islands, Micronesia

The diogenid hermit crab genus Pseudopaguristes McLaughlin, 2002 is currently represented by 15 species worldwide. In this study, we describe a new species of the genus, P. flavioculus, based on a unique male holotype from off Sarigan, Northern Mariana Islands, Micronesia, at depth of 131–133 m. The new species appears similar to the type species of the genus, P. janetkae McLaughlin, 2002, but the lack of conspicuous spines on the dorsal face of the right cheliped carpus, the possession of a median row of tiny spines on the dorsal face of the left cheliped carpus, and different colour pattern of the cephalic appendages and the ambulatory legs distinguish P. flavioculus n. sp. from P. janetkae. Pseudopaguristes has been differentiated from the two allied genera, Paguristes Dana, 1851 and Areopaguristes Rahayu, 2012, by the possession of eight functional pairs of gills (versus 13 pairs in Paguristes and 12 pairs in Areopaguristes), but our examination of the new species and three other congeneric species available for study clarifies that the development of arthrobranchs on the maxillipeds 3 and chelipeds is rather variable in species currently assigned to Pseudopaguristes. Careful observation of the anterior arthrobranchs is recommended to avoid misinterpretation in the counts of gill numbers.