Crosnierocaris athanasoides gen. et sp. nov., a new deep-water alpheid shrimp from the Mozambique Channel (Malacostraca: Decapoda: Caridea).

A new alpheid shrimp genus, Crosnierocaris gen. nov., is established for Crosnierocaris athanasoides sp. nov., a very peculiar shrimp possibly associated with decomposing sea grass accumulations in deeper water. The type series of C. athanasoides sp. nov. was collected in the Mozambique Channel, north of Grande Glorieuse Island, at a depth of 240255 m. The new genus presents a unique combination of morphological features, including the very long, slender rostrum armed with a subdistal ventral tooth; the pterygostomial angle projecting as a strong sharp tooth; the third to fifth pleura with their distoventral margins armed with two to four small teeth, a unique feature within the Alpheidae; the sixth pleuron with an articulated plate; the eyes largely exposed dorsally and laterally; the first pereiopods (chelipeds) feebly enlarged in both sexes, stouter but shorter than walking legs; the first pereiopod carpus with rows of short serrulate setae on its mesial surface; the second pereiopod carpus with five subdivisions; the third to fifth pereiopods with meri armed with stout cuspidate setae; the uropodal diaeresis with a strongly dentate lateral portion; and the complete gill-exopod formula, with mastigobranchs on coxae of the third maxilliped and first to fourth pereiopods. Within alpheid shrimps, the rostrum of C. athanasoides sp. nov. is one of the longest relative to the total body length, often reaching half of the carapace length. The phylogenetic position of Crosnierocaris gen. nov. within the Alpheidae remains to be determined, but based on its morphological characters, the new genus appears to be closest to Athanas Leach, 1814, especially in the configuration of the frontal area of the carapace, and Potamalpheops Powell, 1979, for instance, in the armature of the uropodal diaeresis and walking legs, as well as the presence of setal rows on the cheliped carpus. The new genus also shares several morphological features with Yagerocaris Kensley, 1988, which represents one of the least derived lineages within the family Alpheidae.