Not stated. The specific epithet elegantula is a Latin adjective meaning 'small and elegant'.
Blake, James A. (1984). Four new species of Spionidae (Polychaeta) from New Zealand, with comments on a syntype of Spio aequalis Ehlers from Chatham Island. Proceedings of the Biological Society of Washington. 97(1): 148-159. available online athttps://biodiversitylibrary.org/page/34553466