Owenia Delle Chiaje, 1844; Nilsen & Holthe, 1985; Blake, 2000.
Ammochares Grube, 1846.
Ops Carrington 1865.
Emended diagnosis: Body thick and rigid. Head with prostomial tentacular crown. Anterior elongate mouth surrounded by membranous lips. Anterior three segments with capillaries only; third notopodia dorsal with respect to other anterior notopodia. Biramous segments with capillaries on notopodia and more than 20 irregular rows of bidentate uncini with teeth always arranged side by side on neuropodial tori. Pygidium as a terminal rim or with a pair of weakly developed lobes. Tube generally tapering towards both ends and covered with foreign objects imbricated like roof tiles.
Type species: Owenia fusiformis Delle Chiaje, 1844, by original designation.
Remarks: Some of the features on the tree (Fig. 1B) that appear as synapomorphies of this genus, such as the presence of a peristomial collar or the presence of eyespots, are actually absent in some species not considered in the present study (see for example Ford & Hutchings, 2005) and therefore they have not been included in this emended diagnosis. The type species was widely reported from around the world from intertidal to deep waters (e.g. Hartman, 1959; Dauvin & Thiébaut, 1994). However, more recently this cosmopolitan pattern has been questioned and a series of cryptic species have been described (e.g. Koh & Bhaud, 2001; Koh et al., 2003; Ford & Hutchings, 2005) or genetic lineages suggested (Jolly et al., 2006). Suites of new characters have been shown to be useful to separate species (e.g. Blake, 2000; Koh & Bhaud, 2003; Ford & Hutchings, 2005).