Riggia acuticaudata sp. nov. is described on the basis of 10 female specimens recovered from the body cavity of the freshwater catfish, Ancistrus sp. The fish were caught in a stream called the Corrego Piraputanga, a tributary of the Paraguai River. The new species differs from the others in the genus by being smaller and less convex and by having a pleotelson that tapers abruptly rather than being the same width throughout. Also, the pereopods and dactyls are much smaller, the maxillule has two terminal and three subterminal spines and the first two pleopods are elongate and acute. Additionally, R. acuticaudata sp. nov. is from a different Order of fish host and a new geographic area.
Isopod parasite; cymothoid; fish parasite; Brazil