Remarks. Pseudopotamilla is represented by some boring species in rocks and dead coral, and characterized by the presence of unpaired proximal compound radiolar eyes on the outer margins of radioles. The type species, Pseudopotamilla reniformis (Bruguière, 1789), was originally described from Iceland and has been subsequently reported from the Caribbean Sea, European waters, American coasts of North and South Atlantic, Arctic, and North Pacific (Kolbasova et al. 2013 and references therein).
As shown in her poster presented during the 8th International Polychaeta Conference in Madrid, Knight-Jones, Darbyshire and Petersen were working on the designation of a neotype for Pseudopotamilla reniformis and the resurrection of two species previously synonymized with P. reniformis (Knight-Jones et al. 2004); however, Knight-Jones and Petersen died before this work was completed, but the designation of a neotype is now under revision (Knight-Jones et al. 2017). In addition, records of P. reniformis from the Caribbean area were corrected as P. fitzhughi (Tovar-Hernández & Salazar-Vallejo, 2006), and those from Australia were reassigned as Pseudopotamilla sp. A and sp. B by Capa (2007), showing that some misidentifications of Pseudopotamilla species have occurred. A full revision of Pseudopotamilla is needed in order to confirm the distribution of P. reniformis.
Pseudopotamilla was emended by Capa (2007). The genus includes 16 species (Capa et al. 2014), but only one was described from South America: P. polyophthalma Hartmann-Schröder, 1965 from Punta Lavapie (Central Chile) to 58 m depth. In the present paper, a new species of Pseudopotamilla is described from Argentina, and Potamilla platensis Hartman, 1953, is transferred to Pseudopotamilla and redescribed. Pseudopotamilla platensis is commonly found in translucent, chitinous tubes with an external layer of sand grains, from intertidal to 200 m depth, whereas P. knightjonesae sp. nov., was collected intertidally in hard sediment matrix.