Fresh-water Shrimps (Crustacea, Decapoda, Natantia) of the Orinoco Basin and the Venezuelan Guayana

Shrimps of the families Sergestidae and Palaemonidae collected in the Orinoco basin, the upper Cuyuni River, and the upper and lower Rio Negro, are dealt with in this paper. New records and comments are given for Acetes paraguayensis, Macrobrachium amazonicum, M. brasiliense, M. jelskii, M. nattereri, M. surinamicum, and Palaemonetes carteri. Two new palaemonids are described: Macrobrachium cortezi, a form related to M. nattereri, from several localities in the Orinoco River and upper Rio Negro, and M. aracamuni, from an altitude of 680 m in the Cerro Aracamuni in the drainage area of the upper Rio Negro. Another previously undescribed species of Macrobrachium is recorded but not named due to the lack of mature males.