Taxonomic and Biogeographical Status of Three Species of the Spider Crabs of the Genus Acanthonyx Latreille, 1828 (Majoidea: Epialtidae) as Determined by DNA Barcoding and Morphological Analyses Along the Western Atlantic.

Ana Francisca Tamburus and Fernando Luis Mantelatto (2016) The genus Acanthonyx Latreille, 1828 contains 17 valid species, including A. dissimulatus Coelho, 1993, A. petiverii H. Milne Edwards, 1834 and A. scutiformis (Dana, 1851), which occur along the Brazilian coast. The high degree of intraspecific variation in the angle of hepatic region, size of the tubercles of the carapace and length of setae on the carapace and pereopods has resulted in difficulties with the taxonomy of this genus. Analysis of more consistent morphological and molecular characters are required to clarify the status of the three species that occurs in Brazil. For the molecular data, we used the barcode region of the mitochondrial gene COI as a marker, and we correlated this with morphological characters of adults and juveniles. The three species of Acanthonyx were morphologically similar and the matrix of genetic distances and maximum likelihood trees showed that A. dissimulatus and A. scutiformis belonged to the same group with A. petiverii. They could not be separated using the diagnosing characters proposed in the original description or genetically (present study), thus indicating that the taxonomic status of the first two species is questionable. The division into two distinct groups corresponding to A (Caribbean, Brazil, Venezuela) and B (USA, Mexico) was well supported and indicated that there are genetic differences between these populations. Present study suggests the existence of a single species in Brazil and Caribbean, assigned to A. petiverii (type locality in Antilles). The existence of a new species restricted to North America confirms the cryptic diversity within Acanthonyx.