Use of morphological characters for species separation within the genus Artemia (Crustacea, Branchiopoda)

Abstract

Doubts have been raised about the use of morphological characters as criteria for species separation within the genus Artemia because of their relative validity. The characters considered to date, i.e. morphology of the frontal knobs of the male and the presence/absence of a spine-like projection on the basal part of the penis, are only partly efficacious, since they allow us to reliably distinguish only the Mediterranean species, Artemia salina, from the other bisexual species. While A. salina is characterized by subconical frontal knobs and the absence of the spine-like projection, the other species present subspherical frontal knobs and the spine-like projections. There is no information about the aspect of the frontal knobs in the Asian bisexual species. The aim of the present study is to clarify the situation by means of SEM observations of characters not considered in detail (ornamentation of the apical part of the spine-like projections) and by examination of the frontal knobs in the Asian species, which were not described at the time of the first studies.