Primer registro del poliqueto dulceacuícola <i>Stratiodrilus brevicirrus</i> Amato <i>et al., </i>2004 (Histriobdellidae, Polychaeta) en Argentina

A total of 600 polychaete species are known in Argentina, mostly marine. Freshwater representatives are poorly documented, with only 22 species reported for the Neotropical region. This study presents the first record of Stratiodrilus brevicirrus (Histriobdellidae, Polychaeta) in Entre Ríos Province, Argentina, extending its known distribution from southern Brazil into the Pampean region. Specimens were collected during seasonal macroinvertebrate surveys in 2021 across streams of the Lower Uruguay River Basin. A total of 42 individuals were found in rocky and vegetated substrates and identified using updated taxonomic keys. Voucher specimens were deposited in the Museo Ciencias Naturales de La Plata. This is the second record of the genus Stratiodrilus in the country and the first for this species. Although collected free-living, known host families (Aeglidae and Trichodactylidae) were also present. This record highlights the importance of surveying underexplored freshwater systems, provides new data for national species checklists, and supports future conservation planning in fluvial environments.