Taxonomic status of the species of Pinnixinae Stevcic, 2005 (Brachyura: Pinnotheridae) from the Brazilian coast: an integrativa analysis with morphology and genetics

Abstract

The family Pinnotheridae is composed of small marine crabs that possess commensal relationships with other animals such as annelids, mollusks, echinoderms, and even other decapods. Due to the small size and great morphological similarity between the species of the group, which causes conflicts when it comes to identification and species delimitation, the family still possesses several taxonomic problems and uncertainties. The subfamily Pinnixinae, which includes crabs with a carapace much wider than long that are commensal with other decapods, stomatopods or annelids that inhabit tubes or burrows, involves some of these problems and uncertainties. Among the 12 valid species found on the Brazilian coast, the majority still has a problematic taxonomic status. Some species remain with an uncertain generic position after the division of the genus Pinnixa into Austinixa, Rathbunixa, Tubicolixa, Scleroplax e Sayixa, like Pinnixa gracilipes. Furthermore, there is still conflict regarding the validity of some species of the group, like Austinixa bragantina and Tubicolixa rapax. In addition, due to the great intraspecific morphological variability of the species belonging this subfamily, there are doubts regarding the presence of cryptic species or species complexes in some taxa, such as Austinixa aidae, A. patagoniensis and Tubicolixa chaetopterana. There is also some uncertainty when it comes to the position of the genus Alarconia, which is now classified as a genus within the Pinnixinae subfamily, but possesses great morphological similarity with members of the Pinnixulalinae subfamily. Due to this large amount of uncertainties and problems in this group's taxonomy, an integrative analysis including morphological and molecular evidence will be performed, with the objective being to understand the relationships among the species of the subfamily Pinnixinae found on the Brazilian coastline, to search for cryptic species and to verify the validity of these taxa. The morphology of these specimens will be analyzed under a stereomicroscope, with the main focus being to find morphological characters with taxonomic relevance, especially those that have not been mentioned in previous literature that can be used as diagnostic or those that have some degree of variation. The molecular data will be acquired through a process of DNA extraction of the different species from several localities along the Brazilian coast, amplification through PCR, purification and sequencing to obtain partial sequences of the mitochondrial genes 16S and 12S and the nuclear gene H3, all of which possess great relevance in phylogenetic analysis of the group. Phylogenetic trees with molecular evidence will be constructed using the Maximum Likelihood and Bayesian Inference methods, with the objective of contextualizing the different taxa within Pinnixinae.