Diagnosis. Prostomium frontally entire. Buccal lips paired globular structures on prostomial postero-ventral surface. Antennae absent in most genera (few taxa with onethree antennae). Peristomium two rings, separation between rings distinct dorsally and laterally; first ring ventrally incomplete, second ring projected forward ventrally as muscular lip. Nuchal organs dorsolateral. Parapodia subbiramous; notopodia small knobs, with notoaciculae (few taxa with well-developed dorsal cirri); neuropodia well-developed in all taxa. Without ventral cirri. Branchiae absent in most genera (when present, associated to parapodial lobes of anterior chatigers or over dorsum in posterior chaetigers). All taxa with limbate chaetae; other chaetae variously present in genera: simple and composite multidentate hooded hooks, compound spinigers, simple bidentate hooded hooks, and limbate simple multidentate hooded hooks. Maxillary apparatus symmetric, labidognath-type, with up to six pairs of maxillae.
Apomorphies: Peristomium two rings, separation between rings distinct dorsally and laterally; first ring ventrally incomplete, second ring projected forward ventrally as muscular lip.. Maxillary apparatus symmetric, labidognath-type.