Abstract
For nearly a century the species concept used for the Crustacea Leptostraca has been very wide, particularly in the case of the cosmopolitan genus Nebalia. It is shown that the characters upon which this concept rests are unsatisfactory. On the whole chaetotaxonomic characters in the Leptostraca are, with exceptions, variable and growth-related and thus not well suited for identification of species. On the other hand the shape and proportions of parts provide constant and reliable characters. Against this background the principles for working on leptostracan taxonomy are laid down and a model for description of species is presented. It is shown that species decriptions should always be based on females.
The model is applied in a revision of the leptostracan species of the European shelf. Five species of Nebalia are recognized, two of them new to science, and a new genus, Sarsinebalia, is introduced with {Nebalia typhlops G.O. Sars as genotype. It is demonstrated that in their geographical distribution leptostracan species, far from being more or less cosmopolitan, conform to patterns found in other benthic invertebrate species.
