Abstract The present paper describes a new species of freshwater crayfish of the genus Parastacus Huxley, 1879 from the municipality of Amaral Ferrador in the state of Rio Grande do Sul, southern Brazil, evaluates its conservation status according to the IUCN Red List Criteria (sub-criterion B1), and updates the identification key for the genus. Parastacus longidactylus sp. n. differs from all analyzed species by the large eyes, the prominent and wide rostral carinae, surpassing the rostral basis and extending to the proximal third of the postorbital carinae, postorbital carinae and rostral carinae prominent and with similar lengths, chelipeds carpus dorsomedial surface not divided longitudinally by groove and long dactylus, surpassing the fixed finger. The possible extent of occurrence was estimated to be 6,968 km² and the species was recorded in only one location in the Camaquã River basin. The main threats to the region are the replacement of native vegetation by crops and livestock, water pollution and soil erosion. However, because there is only one known location where Parastacus longidactylus sp. n. occurs we suggest classifying the species as Data Deficient.

Balloniscus glaber sp.n., is described from Rio Grande do Sul, Brazil.