The genus Milnesium doyère, 1840 (Tardigrada) in south America with descriptions of two new species from Argentina and discussion of the feeding behaviour in the family milnesiidae

Abstract

Background: The diversity and distribution of the tardigrades in South America are rather poor and selective, as is information about their feeding behaviour and diet. To date, only ca. 210 tardigrade taxa have been reported from the region of South America. In the present paper, we provide an update of the distribution of the genus Milnesium in South America and discuss some aspects of the feeding behaviour in the family Milnesiidae. Results: In seven moss samples collected in the Argentinean province of Río Negro, 31 specimens, 4 exuviae and 32 eggs belonging to the genus Milnesium were found. Among them, four species were identified: Milnesium argentinum sp. nov, Milnesium beatae sp. nov, Milnesium brachyungue and Milnesium granulatum. By its dorsal sculpture, M. argentinum sp. nov. is most similar to M. beatae sp. nov, Milnesium beasleyi and Milnesium berladnicorum, but it differs from M. beasleyi and M. berladnicorum mainly by having a different claw configuration and from M. beatae and M. beasleyi by having stylet supports inserted in a more caudal position and by some other morphometric characters. In the width of its buccal tube and the claw configuration [3-3]-[3-3], M. beatae sp. nov. is most similar to Milnesium bohleberi, M. brachyungue and Milnesium eurystomum, but it differs from themmainly by having a sculptured dorsal cuticle and by some other morphometric characters. Conclusions: The study discusses distribution and taxonomic problems of the Milnesium species known from South America. As of now, nine Milnesium taxa are known from this region (including two new species reported in this paper). Additionally, the study broadens our knowledge of tardigrades' feeding behaviour, provides some details about their diet and suggests that the type of prey chosen by some species belonging to the family Milnesiidae may be associated with the width of their buccal tube.