A partial revision of the spionid polychaete genera
Spio and
Microspio is presented. The genus
Spio is defined as having branchiae from setiger 1 and the genus
Microspio from setiger 2. Of 74 species originally described in, or transferred to, these genera, 25 species of
Spio and 15 species of
Microspio are accepted as valid, based on the examination of type specimens of 18 species, description of three new species, and the recognition or general acceptance of other species by published systematists. Detailed descriptions are given for
S. filicornis Müller,
S. setosa Verrill,
S. limicola Verrill,
S. pettiboneae Foster,
M. pigmentata (Reish), and
M. microcera (Dorsey). Three new species are described:
S. thulini from Georges Bank, and
M. profunda and
M. tetrabranchia from deep water. A new name,
S. blakei, is proposed for
S. pacifica Blake and Kudenov because the species name is preoccupied by
S. martinensis pacifica Berkeley. Based on the examination of type specimens, the following revisions are made:
M. maculata (Hartman) and
M. theeli Söderström are transferred to the genus
Spio;
S. punctata Hartman is transferred to the genus
Malacoceros; Holmquist's synonymy of
S. arctica (Söderström) with
S. limicola Verrill is confirmed;
S. martinensis pacifica Berkeley is synonymized with
S. filicornis; and
S. armata (Thulin) and
M. gracilis (Hartmann-Schröder) are considered incertae sedis.
