Abstract
Long-term monitoring programs are valuable tools in understanding invasion dynamics. We report the detection of a non-native sabellid polychaete in the La Grange Pool of the Illinois River, Illinois, USA, during 2023. Based on morphological and genetic evidence, we identified this species as Laonome xeprovala, a freshwater and brackish water tube-dwelling suspension feeder first described in Europe with unknown native range. Despite extensive benthic and substrate sampler macroinvertebrate surveys conducted in the Midwest, no sabellid polychaetes had been previously observed and this is thus the first confirmed record of L. xeprovala in Midwestern United States. We encountered common L. xeprovala in both main channel and backwater habitats of the river, while individuals were also recovered from a single ponar grab. L. xeprovala were found in 86.4% of all passive gear samples (Hester-Dendy/rock bags) and 7% of all active gear samples (Ponar), suggesting an established and wide distribution of the species in the region. Potential impacts of this species are not known, but continued monitoring of range and abundance will provide insight into future distribution and impact in Midwestern waterways.