Type species: Opisthodonta pterochaeta Southern, 1914, designated by San Martín & Hutchings (2006).
Diagnosis. Relatively long body, with numerous segments. Palps foliaceous, approximately triangular in shape, basally fused. Prostomium ovate to pentagonal with three antennae, two pairs of eyes and one pair of anterior eyespots. Peristomium with two pairs of cirri. Long and slender antennae and cirri throughout, smooth, distally tapering; ventral cirri usually triangular. Compound chaetae as falcigers and, frequently, also spiniger-like chaetae. Aciculae, at least of anteriormost chaetigers, distinctly expanded distally, with rounded tip. Pharynx long, with tooth away from anterior margin; trepan absent; proventricle massive but shorter than pharynx. Reproduction by epigamy (cf. Ramos et al. 2010).
Remarks. The genus currently includes two known species, the type-species S. pterochaeta, from the Northeastern Atlantic (San Martín 2003), also reported from Australia (San Martín & Hutchings 2006), and S. exsulis Ramos, San Martín & Sikorski, 2010, from the Sub-Arctic and North Atlantic Ocean (Ramos et al. 2010), recently also found off Canary Islands (Jorge Núñez, personal communication).
This is the first occurrence of the genus for the Brazilian coast.