Chaetozone Malmgren 1867

Genus Chaetozone Malmgren, 1867

Type species: Chaetozone setosa Malmgren, by monotypy.

Diagnosis. Prostomium blunt to conical, peristomium elongate to short, usually lacking eye spots, 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 achaetous anterior segment, or rarely an anterior setiger. First pair of branchiae arising from an achaetous segment or first setiger; or sometimes with first two pairs of branchiae on a single anterior segment. Body basically thick and fusiform over many segments, rarely with middle or posterior body segments beaded or moniliform. Setae include capillaries on most setigers and acicular spines in neuropodia and/or notopodia, spines typically concentrated in posterior segments, forming distinct cinctures with spines emerging from elevated membranes; cinctures with few to many spines and with none to many alternating capillaries; some species with posterior noto- and neuropodial sigmoid acicular spines numerous, encircling entire posterior parapodia; 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 capillaries, sometimes limited to gravid individuals. Pygidium a simple lobe, disk like, or with long, terminal cirrus.

Remarks. With an increasing number of species of Chaetozone being described, further details of the peristomium, anterior segmentation, position of the dorsal tentacles and branchiae, nature of the posterior cinctures and associated noto- and neuropodial acicular spines, and pygidium are changing the manner in which species of this genus are viewed. Distinct groups of species that share contrasting suites of characters are now evident. The generic diagnosis presented here is slightly altered from that of Blake (1996, 2006) but does not entirely reflect the diverse morphology now evident in this genus. Some aspects of this morphology are reviewed in the discussion at the end of this paper. The following description of the lectotype of C. setosa selected by Petersen (1999) is intended to better define the type-species of the genus to allow for comparison with the numerous global records referred to the species.