Aphelochaeta Blake, 1991

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 : 152-153

Genus Aphelochaeta Blake, 1991

Type-species: Tharyx monilaris Hartman, 1960 . Original designation by Blake (1991).

Diagnosis. (after Blake 2018). Prostomium conical to rounded; peristomium elongate with pair of grooved dorsal tentacles arising either on or anterior to setiger 1. Anterior segments often expanded, crowded or uncrowded; abdominal segments sometimes beaded or moniliform in appearance; setae simple capillaries lacking distinct serrations using light microscopy but distinct fibrils may be visible using SEM; posterior end frequently expanded, tapering to a simple pygidial lobe.

Remarks. As part of a revision of the genus Tharyx, Blake (1991) assigned bitentaculate cirratulid species having only simple, non-serrated capillary setae to a new genus, Aphelochaeta . The absence of setae other than simple capillaries means that systematists are required to use body shape, details of the pre-setiger region, origin of the dorsal tentacles and anterior branchiae, presence or absence of dorsal and ventral grooves and ridges, form of the posterior end, nature of the pygidium, and Methyl Green staining patterns to identify species. Blake (2018) reviewed a wide range of morphological details that are available within the genus, but species of Aphelochaeta are the most difficult of the bitentaculate cirratulids to identify.

In the present study, six species of Aphelochaeta have been identified. Most specimens are long and threadlike, but, fortunately, each species has a distinct set of characters that makes identifications possible if the specimens are in good condition. There are differences in the size and configuration of the pre-setiger region including presence or absence of annular rings on the peristomium, differences in the placement of the dorsal tentacles and first branchiae, development of parapodia, and MG staining patterns.