Axiokebuita australis, Blake, 2023

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 : 277-279

Axiokebuita australis sp. nov.

urn:lsid:zoobank.org:act:C93CC779-84C1-4FC0-8252-FEE01BBA2968

Figs 3–4

Holotype: eastern Australia, continental slope off Tasmania, Freycinet Marine Park , RV Investigator, Sta. 011, coll. 19 May 2017, box core, 41.721°S 149.125°E, 2793 m ( AM W.52681) . Paratypes (2): same data as holotype (1, AM W.53989); abyssal plain off southeastern Victoria, East Gippsland Marine Park , RV Investigator, Sta. 033, coll. 24 May 2017, Brenke Sled, distance 2.6 km, 38.521°S 153.213°E 4107 m to 38.498°S 150.207°E 4064 m, dissected in part for DNA (1, AM W.52695 ) .

Description. All three specimens complete: holotype (AM W.52681) with 22 setigers, 10. 55 mm long and about 1.8 mm wide; paratype from Sta. 011 (AM W.53989) with 19 setigers, 8 mm long and 2 mm wide; paratype (AM W.52695) from Sta. 033 complete, but damaged and in two parts, with 19 setigers, about 6 mm long, about 1.2 mm wide (posterior section removed for DNA). Body thick, sausage-shaped; more or less rectangular in cross section ( Fig. 3A, C ), without dorsal or ventral grooves or ridges along body. Segments with one or two rows of elevated pads across dorsum; setigers 1–4 with a biannulate pattern ( Fig. 4A ); most of body with uniannulate segments; ventrally, each anterior and middle segment with one to four annulated rows, these narrow, with separate raised pads indistinct, appearing more or less as single elevated ridge; posteriorly ventral surfaces with a single row of raised pads more or less continuous with dorsal rows ( Fig. 3C, D ). Colour in alcohol light tan with no pigmentation.

Prostomium pentagonal in shape ( Figs 3A, B , 4A ), straight across anterior end with two thick lateral horns arising from narrow subterminal sides ( Figs 3A, B , 4A ), followed by long curving borders meeting mid-dorsally; eyes absent, nuchal organs not observed. Peristomium irregularly encompassing prostomium dorsolaterally ( Figs 3A, B , 4A ) and surrounding mouth ventrally; proboscis emergent, with numerous elongate lobes surrounding oral opening ( Figs 3B , 4A ); neck organs observed on paratype (AM W.52695) as a pair of swellings ventrolateral on enlarged oral area; these obscured on holotype and other paratype due to ventral curvature and compression of entire pre-setiger area.

Parapodia reduced to blister-like swellings throughout, with noto- and neurosetae arising from notch on posterior sides. Notopodia with single short, oval to rounded postsetal lamella, this less conspicuous in posterior setigers; neuropodia with an elongate, fingerlike lamella; both lamellae from setiger 2 or 3 continuing to posterior end ( Fig. 4B ). Setae all thin capillaries in spreading fascicles throughout; furcate setae not observed. Notosetae long, with up to 35–45 per fascicle.

Pygidium a simple plate composed of 6–8 thickened lobes surrounded anal opening ( Fig. 3D ).

Remarks. Axiokebuita australis sp. nov. is most similar to A. millsi , the type-species, in lacking papillated pygidial lobes. Specimens of A. millsi from off New England in bathyal depths were observed as part of a separate study (Blake in preparation) to have a fusiform-shaped body, two large non-papillated lobes around the anal opening, and 2–3 rows of annulated pads along the body; these observations agree with the published observations of Pocklington and Fournier (1987) from off Nova Scotia. In contrast, A. australis sp. nov. has a sausage or grub-shaped body, 6–8 small lobes around the anus, and two annulated rows of pads on setigers 1–4 but only a single row along the rest of the body.

Etymology. The epithet is from the Latin australis , in reference to the Australian and Southern Hemisphere location of this species.

Biology. Holotype (AM W.52681) and paratype (AM W.53989) with numerous oocytes in coelom measuring 80–100 µm in diameter.

Distribution. Continental slope and abyssal plain off SE Australia, Tasmania and Victoria, 2793–4064 m.

Figures

Figure 3. Axiokebuita australis sp. nov. (A) Anterior two thirds of holotype, lateral view; (B) detail of pre-setiger region of same; (C) entire paratype in dorsolateral view; (D) posterior end, right lateral view. A, B, holotype (AM W.52681); C, D, paratype (AM W.53989). All stained with Shirlastain A.

Figure 4. Axiokebuita australis sp.nov.(A) anterior end, dorsal view; (B) setiger 9, anterior view.A, paratype (AM W.53989); B, holotype (AM W.52681).