Chaetozone Malmgren 1867

Genus Chaetozone Malmgren, 1867

Type species: Chaetozone setosa Malmgren, 1867, by monotypy.

Diagnosis. (Emended, after Blake 2015). Prostomium blunt to conical, peristomium elongate to short, usually lacking eyespots, with a pair of small nuchal slits or depressions at posterior edge; with a single pair of grooved dorsal tentacles arising from posterior edge of peristomium, or sometimes more posterior on an asetigerous anterior segment, or rarely on an anterior setiger. First pair of branchiae arising from an achaetous segment or first setiger; sometimes with first two pairs of branchiae on a single anterior segment. Body usually expanded anteriorly and narrowed posteriorly, rarely with middle or posterior body segments beaded or moniliform; posterior end often expanded. Setae include capillaries on most setigers and sigmoid acicular spines in neuropodia and notopodia, with spines typically concentrated in posterior segments forming distinct cinctures with spines carried on elevated membranes; cinctures with few to many spines sometimes encircling entire posterior end, accompanied with none to many alternating capillaries; bidentate spines sometimes present in juveniles or occasionally in ventral-most position of far posterior setigers of adults, accompanying unidentate spines in cinctures; some species with long, natatory-like capillary notosetae, sometimes limited to gravid individuals. Pygidium a simple lobe, disk-like, or with long, terminal cirrus.

Remarks. Blake (2015) emended the genus Chaetozone, described the lectotype of C. setosa, added eight new species, and reviewed more than 20 species from North America. He effectively limited the genus to species having numerous elongate acicular spines in both noto- and neuropodia that form a prominent and conspicuous armature in modified parapodia of posterior segments. A few other species having few or inconspicuous spines, or spines limited to the neuropodia, are here referred to the genus Chaetocirratulus n. gen. (see above).

Species of Chaetozone from Antarctica that agree with the definition presented here have historically been referred to the type-species, C. setosa by Hartman (1967, 1978) and Hartmann-Schröder & Rosenfeldt (1989, 1990). With the recent redescription and restriction of the range of C. setosa to the Arctic (Chambers 2000; Blake 2015) and description of numerous new species from worldwide locations, many of which were formerly referred to C. setosa (Blake 1996, 2006, 2015; Doner & Blake 2006; Dean & Blake 2007; Magalhães & Bailey Brock 2013; Elías et al. 2017, and others) it is apparent that the Antarctic species of Chaetozone remain poorly known.

In the present study, five species of Chaetozone are reported from western South America, two new and seven species are reported from Antarctica, five new. Two species of Caulleriella, C. bransfieldensis, and C. homosetosus described by Hartmann-Schröder & Rosenfeldt (1989) from the Antarctic Peninsula are here referred to Chaetozone.