In water, no one can hear you scream: a new species of parasitic isopod from the genus Zeuxokoma Grygier, 1993 (Isopoda: Epicaridea, Cryptoniscidae) infesting a snapping-shrimp (Caridea, Alpheidae) from Brazil.

Isopods of the suborder Epicaridea Latreille, 1825 are obligatory parasites of other crustaceans, using them as intermediate and definitive hosts during their life cycles. All species of the family Cryptoniscidae Kossmann, 1880 are endoparasitic or mesoparasitic, and can be found as direct parasites of decapods or as hyperparasites of rhizocephalan barnacles infesting decapod hosts. Females usually lose all body segmentation, lacking antennae, pereopods, oostegites and pleopods, and their bodies have two portions, an anterior portion that is embedded in the host cuticle and a posterior one that is external to the host. Males, on the other hand, are neotenous, and retain the morphology of the cryptoniscus larval stage. The genus Zeuxokoma Grygier, 1993 comprises six valid species, all of which are direct parasites of caridean shrimps in the Atlantic and Pacific Oceans. Here we describe a new species of Zeuxokoma parasitizing the snapping-shrimp host Synalpheus apioceros Coutière from Brazil. The new species is morphologically most similar to Z. setosa (Nierstrasz & Brender à Brandis, 1930), but can be distinguished by the position of the shield and the insertion of the trunk. We also comment on the morphology of the last embryonic stage, provide a map detailing the distribution of all currently valid species of Zeuxokoma, and construct a key based on the females to assist in the identification of species. Finally, we include a table compiling the morphological characters, definitive hosts, and known distribution of the females of each species.