Identity uncertain? Invalid as a homonym but the taxon was questionably referred to be a synonym of Spio filicornis (Müller, 1776) by Soderstrom (1920). However, 1) McIntosh erected this name for Spio filicornis sensu Malmgren, and 2) there are multiple Spio species similar to S. filicornis in Europe.
McIntosh, William Carmichel. (1915). Polychaeta, Opheliidae to Ammocharidae. A Monograph of the British Marine Annelids. The Ray Society, London, 3 (1): i-viii, 1-368 (text). available online athttps://biodiversitylibrary.org/page/38532650