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

This article focuses on the taxonomy, morphology, molecular phylogeny, and host associations of two endoparasitic entoniscid isopods from mud and stone crabs along the western Atlantic coast: Cancrion carolinus and a newly described genus and species, Cryptocancrion brevibrachium. Both species are cryptic and cannot be reliably distinguished by adult female morphology alone, but differ in larval morphology—C. carolinus has "long-armed" epicaridium larvae, while C. brevibrachium has "short-armed" larvae—and molecular data confirm their distinctiveness. These parasites infest multiple brachyuran hosts, including Dyspanopeus sayi, Panopeus herbstii, Rhithropanopeus harrisii, Eurypanopeus depressus, and Menippe mercenaria, with overlapping geographic distributions along the U.S. Atlantic coast and Gulf of Mexico. The study also clarifies the uncertain status of Cancrion needleri, considering it a species inquirendum due to lack of larval and molecular data, and highlights the need for larval and genetic analyses to accurately identify entoniscid species given their cryptic nature.