Systematics and description of a new species of Faxonius Ortmann, 1905 (Decapoda: Astacidea: Cambaridae) from the Red River system of Kentucky and Tennessee, USA

Abstract

Faxonius barrenensis (Rhoades, 1944) is endemic to the Green River system of Kentucky and Tennessee, USA and closely related to Faxonius mirus (Ortmann, 1931), which is restricted to Tennessee River tributaries in Tennessee and Alabama. A crayfish with morphological affinities to these species (Faxonius sp.) occurs in the Red River system (Cumberland River Drainage) of Kentucky and Tennessee. Whether the latter represents a disjunct population of F. barrenensis, F. mirus, or a distinct species, has not been tested. Whether the shared morphological traits reflect shared ancestry or convergence is unknown. We used molecular and morphological data, including two mitochondrial (COI and 16S) and two nuclear (28S and GAPDH) genes and a standard suite of phenotypic measurements to examine the phylogenetic relationships and the taxonomic status of Faxonius sp., relative to F. barrenensis, F. mirus, and other species of Faxonius Ortmann, 1905. All gene datasets recovered focal taxa as a clade, implying their morphological similarities likely reflect shared ancestry. In all mitochondrial and combined gene trees, Faxonius sp. was recovered as genetically divergent from F. barrenensis and F. mirus. Faxonius sp. is phenotypically distinguished from F. barrenensis and F. mirus based on several characteristics including shorter rostrum, longer abdomen, wider areola, and straight margins on both mandibles (toothed in F. mirus; toothed and straight in F. barrenensis); Form I males have a strong angular shoulder on the gonopod, in comparison to F. barrenensis. Given these findings, we describe Faxonius sp. as Faxonius bellator n. sp. Faxonius bellator n. sp. has been collected at only four localities, suggesting it has a small range and warrants conservation concern.