A new species of
Sphaerosyllis (Polychaeta: Syllidae) has been discovered on shallow sandy bottoms of Balearic Islands. The description of
Sphaerosyllis adelae n.sp. is given. A revision based in the bibliography, with keys of the species is included in the paper, and the division of the genus in two subgenera,
Prosphaerosyllis and
Sphaerosyllis is proposed.
