Morphological and molecular evidence for a new species of the genus Milnesium Doyère, 1840 (Tardigrada: Apochela) from south America

Abstract

Tardigrades are aquatic microinvertebrates, that can be found from the poles to the tropical regions. However, knowledge about their diversity and distribution is still limited, especially regarding the Neotropical region. In addition, many species described in the past were considered cosmopolitan but new morphological, morphometric and especially molecular studies have demonstrated the existence of species complexes. The species Milnesium tardigradum Doyère, 1840 is an example that highlights this issue. Many M. tardigradum records made in South America date from the time when this species was considered cosmopolitan and exhibiting large intraspecific variability. However, current revisions of the genus using modern techniques indicate that the M. tardigradum sensu stricto is most likely restricted to the Palaearctic region. In this contribution, we describe a new species, Milnesium iniquum sp. nov. from south-eastern Brazil, with additional records from Argentina and French Guiana, utilising integrative taxonomy framework. The new species is characterised by having smooth cuticle, presence of dorsal pseudoplates, adult claw configuration [3-3]-[3-3] and [2-2]-[2-2] in hatchlings (early positive CC change), with internal and anterior spurs larger than external and posterior spurs and by presence of short cuticular bars on legs IV.