Cladocères de quelques corps d'eaux du bassin moyen de l'Orénoque (Vénézuéla)

Abstract

The examination of 110 pelagic samples and 16 littoral samples from several water bodies in the middle basin of the Orinoco river (lakes formed by barrage or inundation of the Orinoco and Caroni river systems) revealed 58 taxa of Clado­ cera, of which 24 are new to the Venezuelan launa. Two species, Alona ovata and Bosminopsis macaguensis, are new to science. Alona karelica, a palaearctic species, has never been recorded before on the continent of America. 35 % of the fauna studied are represented by neotropical forms, of which eight are endemic to South America. An illustrated taxonomic section deals with 13 species that are rare or little known. The distribution of species was studied in the environment examined and in the two categories of white and black waters. The richest cladoceran fauna was found in the lakes formed by inundation of the Orinoco, the species diversity being due to littoral forms, chiefly in the Family Chydoridae. In the pelagic environment, white-water bodies were characterised by the species association Moina minuta, Ceriodaphnia cornuta, Bosmina tubicen, and Bosminopsis deitersi, and black-water bodies by the dominance of Bosminidae : Bosmina hagmanni, Bosminopsis macaguensis, Bosminopsis deitersi, Ceriodaphnia cornuta. The case of Daphnia gessneri, generally considered endemic to the Amazon-Orinoco system and present in a single survey, is discussed.