On two allied species of the genus Diastylis from southern South America: D. granulata Zimmer, 1921 and D. argentata Calman, 1912 (Crustacea: Cumacea: Diastylidae)

Abstract

The adult male and female of Diastylis granulata Zimmer, 1921 are herein described on the basis of specimens collected near its type locality. This species was previously known from a single subadult male collected south of the Río de la Plata mouth (Argentina) during the Swedish Eugenie Expedition (1851–53), and has not been reported again since its original description. An allied species, Diastylis argentata Calman, 1912, is briefly redescribed and its northern limit of distribution extended to Puerto Montt (Chile). These two species can be easily distinguished by the arrangement of their carapace sculptures: D. granulata bears an arched row of teeth that ends on each anterolateral horn, whereas in D. argentata this row of teeth extends backwards without reaching the anterolateral horn. SEM photographs showing the carapace sculpturing of these two species are provided.