Generic diagnosis (modified from Borowski 1994). Four or more rows of dorsal and sessile macrotubercles without terminal papillae. Anterior end with a median antennae and a pair of lateral antennae. A pair of ventral palps, similar to antennae is present. A pair of papillae similar in length to antennae and palps may also be present. Chaetae compound. Type species Sphaerodoropsis sphaerulifer (Moore, 1909).
Remarks: Borowski (1994) made no differentiation between palps and antennae in sphaerodorids and indeed they are very similar. However, Rouse & Fauchald (1997) and Pleijel (2001) distinguished them to facilitate comparison with other Phyllodocida. Borowski (1994) stated that Sphaerodoropsis could have an additional pair of antennae but this would make them unique among Phyllodocida so it seems more reasonable to interpret them as elongate papillae (see Discussion). The interpretation of the prostomium, peristomium and anterior segments in the description below follows Pleijel (2001).