Cryptic diversity in endoparasitic isopods (Bopyroidea: Entoniscidae) from mud crabs (Panopeidae) along the Atlantic coast of North America, with the description of a new genus and new species as revealed by molecular and larval characters: the long and the short of it

Abstract Although intertidal crabs from the western Atlantic coast are relatively well studied for some parasite fauna, their parasitic isopods are poorly known. We document two endoparasitic entoniscids (Cancrion carolinusPearse & Walker, 1939 and Cryptocancrion brevibrachiumn. gen., n. sp.) from mud (Brachyura: Panopeidae) and stone (Brachyura: Menippidae) crabs based on molecular and morphological data, including descriptions of their epicaridium larvae. Although these species cannot be distinguished based on adult female characters, molecular data and larval and male morphologies show that two species are present, sometimes sympatrically. The only other species of CancrionGiard & Bonnier, 1887 from the Atlantic coast of North America is Cancrion needleriPearse & Walker, 1939, described from adult specimens parasitizing Dyspanopeus sayi (Smith, 1869) from Prince Edward Island, Canada. Larvae of this species were never described and we consider it a species inquirenda. Cryptocancrion brevibrachiumn. gen., n. sp. is documented to have epicaridium larvae with a “short-armed” morphology (sixth pereopod subequal in length to pereopods 1–5), and the adults parasitize at least three mud crabs: D. sayi, Panopeus herbstiiH. Milne Edwards, 1834, and Rhithropanopeus harrisii (Gould, 1841). By contrast, Cancrion carolinus (originally described from P. herbstii collected in Beaufort, NC, USA) has epicaridium larvae with a “long-armed” morphology (sixth pereopod approximately twice the length of pereopods 1–5) and is found in at least four host species: Eurypanopeus depressus (Smith, 1869), P. herbstii, and R. harrisii and the stone crab Menippe mercenaria (Say, 1818). We describe C. brevibrachiumn. gen., n. sp. and redescribe C. carolinus based on type material and fresh specimens. The cryptic nature of these entoniscids indicates that examination of epicaridium larvae and/or molecular data are needed to properly identify species.