| Summary: | Chaetocirratulus new genus Type species: Heterocirrus andersenensis Augener, 1932. Original designation. Diagnosis. Prostomium broadly rounded anteriorly or wedge-shaped; eyespots absent; with a pair of small nuchal slits or depressions at posterior edge. Peristomium with a single pair of grooved dorsal tentacles arising from posterior margin or interface with setiger 1. First pair of branchiae arising from posterior margin of peristomium, an achaetous segment, or setiger 1. Body typically thick and fusiform over many segments, rarely with middle or posterior body segments beaded or moniliform; individual segments short, numerous. Setae include capillaries on most setigers and thick, pointed acicular spines in neuropodia and a few in notopodia or spines in neuropodia only; spines few, often small and inconspicuous, not forming cinctures. Individual spines straight to weakly sigmoid. Pygidium with a simple ventral lobe. Etymology . The name Chaetocirratulus is derived from the Greek chaeto for hair or bristle and the Latin cirrus for curl or tendril and is a combination of the generic names Chaetozone and Cirratulus emphasizing the close similarity of these bitentaculate cirratulids with their multitentaculate relatives. Remarks. Chaetocirratulus n. gen. is established to accommodate several bitentaculate cirratulids having few acicular spines that do not produce the distinct posterior armature formed of cinctures of numerous sigmoid spines typical of species of Chaetozone . As will be seen, in some Antarctic species, the spines are so inconspicuous that some species were originally described as lacking them and as such, have been misidentified in recent studies when only the characteristics from the original descriptions or those restated by Hartman (1966) were cited. In addition, species of Chaetocirratulus n. gen. typically have a prostomium that is enlarged, broad, or wedge-shaped and an enlarged thickened body, where segments are short and often swollen, producing a fusiform shape that is not divided into ...
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