Phenotypically exceptional Echiniscus species (Heterotardigrada: Echiniscidae) from Argentina (Neotropics)

One of the most extensive species radiations in tardigrade evolution took place Echiniscus phylogenetic line, which contains genus with over 120 described to date. The internal classification is historically based on two major sources variability: chaetotaxy, that arrangement and shape trunk appendages, sculpturing dorsal plates. These criteria allowed for delineation complexes, such as blumi-canadensis or spinulosus group. Recent analyses confirmed they represent monophyletic lineages. However, affinities some have not been sequenced are straightforward given their uncommon morphologies. In this paper, we present five found Argentina, constitute exemplary cases. aonikenk sp. nov. exhibits extraordinarily elongated cirri A , exceeding 50% body length, dorsoventrally flattened spines, including particularly wide spines E . a probable sister group complex. Furthermore, evelinae de Barros, 1942, reported here only third time ever, characterised by an extreme elongation often autapomorphic comprising epicuticular granules, pseudopores, distinct endocuticular reticulum pillars. Analogously E. apparently constitutes separate evolutionary lineage. Finally, pellucidus (the merokensis complex), peruvianus Binda & Pilato, 1994 syn. testudo complex) manuelae da Cunha do Nascimento Ribeiro, 1962 analysed. Morphological peculiarities revealed study discussed light taxonomy.