Chaetozone Malmgren, 1867

Blake, James A., 2019, New species of Cirratulidae (Annelida, Polychaeta) from abyssal depths of the Clarion-Clipperton Fracture Zone, North Equatorial Pacific Ocean, Zootaxa 4629 (2), pp. 151-187 : 170-171

Genus Chaetozone Malmgren, 1867

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

Diagnosis. (after Blake 2018). Prostomium blunt to conical, peristomium short to elongate, 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 asetigerous 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 usually expanded anteriorly, rarely with middle or posterior body segments beaded or moniliform; narrowing posteriorly or posterior end often expanded. Setae include capillaries on most setigers and sigmoid acicular spines in neuropodia and notopodia; spines typically concen- trated in posterior segments, forming distinct cinctures with spines carried on elevated membranes; cinctures with few to many spines sometimes encircling entire individual posterior segments, accompanied with none to many alternating capillaries; bidentate spines sometimes present in juveniles or occasionally accompanying unidentate spines in ventral most position of far posterior setigers of adults; some species with long, natatory-like capillaries, sometimes limited to gravid individuals. Pygidium a simple lobe, disk like, or with long, terminal cirrus.

Remarks. Chaetozone is the largest genus of Cirratulidae with 54 species ( Blake 2018). Species of Chaetozone are characterized by having prominent acicular spines in noto- and neuropodia that in posterior segments arise from elevated podial lobes or membranes that carry the spines and produce a distinctive armature. In some species, the noto- and neuroacicular spines together nearly encircle the posterior segments.

Although widely distributed globally in shelf and slope depths, species of Chaetozone are rare in abyssal depths below 3000 m. To date, only six species have been reported from lower continental slope or abyssal depths greater than 3000 m ( Blake 2006, 2018). These species are mainly in the eastern Pacific and Southern Oceans where upwelling and primary production is high in surface waters, providing a rich nutrient supply to the seafloor. To date, no species have been reported from oligotrophic habitats such as those found at the CCFZ.

In the present study, three species of Chaetozone were identified from the CCFZ samples. All are small and have elongate threadlike bodies that differ from the more robust bodies of typical species of Chaetozone including those from deep water. However, the distinctive posterior spines are present and prominent.