A new species of Ampharete Malmgren, 1866 (Annelida: Ampharetidae) from Washington and redescription of A. cirrata Webster & Benedict, 1887 and A. labrops Hartman, 1961.

Ampharete acutifrons (Grube, 1860), originally described from Greenland, has long been considered a widely distributed arctic-boreal species. However, recent morphological re-assessment of the holotype indicates that most previous records of A. acutifrons were misidentifications, and molecular sequence data also suggest that A. acutifrons is a multispecies complex. This study focuses on specimens of the A. acutifrons species complex from Washington, USA, with publicly available cytochrome c oxidase subunit I (COI) sequence data. Specimens from Washington belonging to the Invertebrate Zoology Collection of the Florida Museum of Natural History were examined. Additional specimens were examined for morphological comparison, including type material of A. cirrata Webster & Benedict, 1887, and A. labrops Hartman, 1961. Detailed morphological descriptions of specimens and photographs of the diagnostic characters were made. The molecular analysis includes 37 published COI sequences of Ampharete and Anobothrus species sourced from public databases. Redescriptions of type material of A. cirrata and A. labrops are provided. Ampharete paulayi n. sp. is described as a new species from Washington, USA, based on morphological and COI sequences data. Photographs of living specimens are presented, a hypothesis on the development of buccal tentacles in Ampharete species is proposed, and the use of Methyl green stain is recommended as a standard practice in future descriptions of ampharetids.