Chaetozone Malmgren, 1867

Blake, James A., 2023, New Species of Cirratulidae (Annelida) from Continental Slope and Abyssal Depths off Eastern Australia, Records of the Australian Museum (Rec. Aust. Mus.) 75 (3), pp. 249-270 : 257

Genus Chaetozone Malmgren, 1867

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

Diagnosis. (Emended from Blake, 2018). Prostomium blunt to conical, elongate to short, usually lacking eyespots, with a pair of small nuchal slits or depressions at posterior edge. Peristomium 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 peristomium, 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, with long, terminal cirrus, or few short lobes.

Remarks. Chaetozone is the largest of the cirratulid genera with about 75 species ( Blake, 2022). Species of Chaetozone are typically recognized by having acicular spines in both noto- and neuropodia and with those of posterior segments frequently numerous and arranged in conspicuous spreading fascicles that often entirely encircle the body providing a characteristic armature. However, several species have a reduced number of acicular spines that are not superficially conspicuous and as such are peripheral to the above definition ( Blake, 2022). In the present study, two species of Chaetozone were identified, but none of the specimens were complete precluding an exact determination of the number of acicular spines and their arrangement in posterior segments. However, the morphology of the pre-setiger region agrees well with other related species of Chaetozone and makes a comparison of soft morphology feasible.