Abstract

Ultrastructural analysis of the cuticle of specimens of Echiniscus rufoviridis Du Bois-Raymond Marcus, 1944, collected in Santa Rosa City (La Pampa Province, Argentina) was carried out to characterize and compare them with those from other species of Echiniscus. The E. rufoviridis cuticle exhibits both specific features and others that are common with other tardigrades taxa of different levels. We propose the existence of two dorsal epicuticular ultrastructural patterns within the genus Echiniscus, i.e. “testudo type” and “viridis type”. Echiniscus rufoviridis shows the “testudo” type of the dorsal epicuticle: lacunar basal layer clearly different from the rest by its greater thickness. E. rufoviridis and E. testudo also share the dorsal intracuticle thickness and the presence of a trilaminar layer between the ventral epicuticle and intracuticle. E. rufoviridis differs from E. testudo by the fewer lacunae layers, by a more abundant interlacunar matrix, and by a more irregular lacunar arrangement in the dorsal epicuticle. On the other hand, the lacunar system in E. rufoviridis communicates with the exterior via wide pores opening in the surface depressions. Also peculiar to E. rufoviridis is the proportion between the basal and apical portions of the striate layer of the ventral epicuticle. Ultrastructural similarities observed between the cuticles of E. rufoviridis and E. testudo agree with similarities in the dorsal sculpture. We suggest that these similarities are related to the ecological parallel of both species.