Axiokebuita Pocklington & Fournier, 1987

Blake, James A., 2023, New Species of Scalibregmatidae (Annelida) from Slope and Abyssal Depths off Eastern Australia, Records of the Australian Museum (Rec. Aust. Mus.) 75 (3), pp. 271-298 : 277

Genus Axiokebuita Pocklington & Fournier, 1987

Type species: Axiokebuita millsi Pocklington & Fournier, 1987 , by monotypy.

Diagnosis. (Emended after Blake, 2020): Body elongate, with segments similar throughout, but some species with a fusiform shape; segments with one to four annulated rings composed of small, inconspicuous elevated pads, best developed on middle and posterior segments; venter with weakly developed median ridge. Prostomium triangular to pentagonal, truncate on anterior margin with long, subterminal ciliated lateral horns; eyes absent, nuchal organs in narrow grooves on posterior part. Peristomium a single, complete ring, weakly incised dorsally, divided into upper and lower lips of mouth ventrally; formed from large expanded lobes; unique paired ciliated “neck organs” present posterior to lower lip of mouth. Parapodia narrow ventral postsetal cirrus. Branchiae absent. Setae all capillaries, furcate and spinous setae absent; long, natatory-like setae present or absent. Pygidium reduced, short anal cirri present or absent; or with two pad-like lobes covered with papillae or papillae absent. Numerous cilia and ciliary patterns, present on lateral horns, prostomium, and interramal papillae; unique paired ciliated patches on ventral side of body.

Remarks. The genus Axiokebuita and type species, A. millsi were originally described from upper slope depths off Nova Scotia ( Pocklington & Fournier, 1987). In the same paper, the authors referred Kebuita minuta Hartman (1967) from Antarctica to their new genus while at the same time referred some of the Antarctic specimens to A. millsi implying that the species was bipolar in distribution. Records of Axiokebuita are few; the literature was reviewed by Blake (2020).

Parapar et al. (2011) examined specimens of A. minuta from Antarctica and among other things, referred the type-species, A. millsi to synonymy with A. minuta thus establishing the species as more or less cosmopolitan and bipolar in distribution. Unfortunately, these authors did not examine any specimens of A. millsi as part of their review. Martinez et al. (2013) recently described a new species, A. cavernicola from marine caves in the Canary Islands.

Several features of Axiokebuita species are reported as characteristic for the genus and differ from most Scalibregmatidae including (1) long thickened subterminal lateral prostomial horns (termed palps by Parapar et al., 2011 and Martinez et al., 2013) that are ciliated and likely assist in feeding and burrowing); (2) the presence of paired sensory “neck” organs on the peristomium ventral to the mouth and separate from the prostomial nuchal organs; (3) a unique pygidium present on some species, that bears a pair of lobes covered with minute papillae; (4) absence of furcate and acicular spines; (5) the presence of ciliary bands on the prostomial horns and elsewhere on the prostomium and body; (6) displacement of the interramal sense organ from a position between the parapodia to a location closer to the notosetae.

Among these characters, the long thickened lateral prostomial horns, neck organs, and absence of furcate setae and acicular spines appear to be more or less consistent among species. However, the pygidial morphology is not consistent and slender spinous setae are known from some specimens ( Blake & Hilbig, 1990).

As part of a larger study of deep-water scalibregmatids, new collections of Axiokebuita millsi and other species are being re-evaluated and compared based on the new characters identified by Parapar et al. (2011). That study when published will serve to update the systematics of this genus and status of the closely related genera Scalibregmides Hartmann-Schröder, 1965 and Speleobregma Bertelsen, 1986 (Blake, in preparation). In the meantime, Axiokebuita australis sp. nov. has been discovered in the deep-water samples collected as part of the RV Investigator IN2017 _V03 survey off Southeastern Australia. That species is here described and compared with other known species.