Abstract
A new genus and species within the family Polymorphidae Meyer, 1931 were erected to accommodate cystacanths recovered from the mesentery of individuals from a non-native population of the red swamp crayfish Procambarus clarkii (Girard), collected from South Carolina (USA). Morphological characteristics of the specimens collected included in both sexes a spindle-shaped body with a slender hindtrunk, two fields of markedly different sized spines on the foretrunk, the presence of a middle row of smaller scythe-shaped hooks on a proboscis armed with 19-20 longitudinal rows of 14-16 hooks; and in males, six cement glands, absence of genital spines, and a digitiform and spinose bursa (observed inverted). Sequencing portions of both the mitochondrial cytochrome c oxidase I (COI) and large subunit ribosomal RNA genes was completed, followed by phylogenetic analysis of a concatenated alignment. Sequences from our specimens appeared in a clade with those of Hexaglandula corynosoma (Travassos, 1915) and Ibirhynchus dimorpha (Schmidt, 1973) but were 27% divergent from both using the COI marker. The genetic divergence of this parasite from other polymorphid genera, along with unique morphological features, justified erecting a new genus and new species. Herein we describe Heterospinus mccordi n. gen. n. sp. bringing the total number of genera within the family Polymorphidae to 16, and we emend and update the latest key that was provided for the genera within this family. This is the first record of polymorphids infecting P. clarkii outside of its native range. The definitive host remains unknown.