Oligobregma bathyala, 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 : 282-287

Oligobregma bathyala sp. nov.

urn:lsid:zoobank.org:act:443CCA0A-F368-4BC0-AA42-CE42A5FF4046

Figs 7–8

Holotype: off eastern Australia, between Victoria and Tasmania, near Bass Strait Marine Park, RV Investigator, Sta. 023, coll. 22 May 2017, Brenke sledge, distance, 2.7 km, 39.462°S 149.277°E, to 39.465°S 149.246°E, 2774– 2694 m ( AM W.52686) . Paratypes (2): same data as holotype ( AM W.52687 and W.52688). Juveniles (2): off Tasmania, Freycinet Marine Park, Sta. 005, coll. 18 May 2017, Brenke Sledge, distance 2.8 km, 41.730°S 149.135°E, to 41.753°S 149.147°E, 2789– 2779 m (2, AM W.53991) .

Description. Three type specimens from Sta. 023 all complete: holotype (AM W.52686) with 28 setigers, 12.2 mm long, 2.8 mm wide across expanded anterior section; 0.6 mm wide across narrow posterior section, and 1.4 mm wide across far posterior pre-pygidial expanded section; paratype (AM W.52687) with 28 setigers, 12 mm long, 2.8 mm wide across expanded anterior section and 0.8 mm wide across narrow posterior section; paratype (AM W.52688) with 26 setigers, 12 mm long, 2.2 mm wide across expanded anterior section and 0.4 mm wide across narrow posterior section.

Setigers 1–4 narrow, with prominent parapodia and setal fascicles ( Fig. 7A ); setigers 5–14 expanded, parapodia reduced to short lobes ( Fig. 8A ); dorsal and ventral cirri developed by setiger 14; setigers 15–28 narrow with prominent parapodia and cirri, five pre-pygidial segments of holotype also expanded ( Fig. 8A ), but not on paratypes. Body with transverse rows of raised pads ( Fig. 7A ): setiger 1 with one row, setigers 2–3 with two rows, setiger 4 with one row, setigers 5–13 with three rows, but mostly obscured in expanded segments; setigers 14–28 with four transverse rows of pads. Venter with similar transverse pad pattern, but interrupted by mid-ventral ridge from about setiger 2, ridge initially a low, rounded elevation, becoming narrow and conspicuous in posterior setigers after expanded section; this ridge with breaks or creases where transverse rows of pads occur. Branchiae absent. Colour in alcohol, light tan.

Prostomium broadly curved across anterior margin, expanded laterally, merging posteriorly with narrow peristomium; with two short, rounded frontal horns emerging subapically from anterior margin ( Fig. 7A ); eyes absent; nuchal organs as grooves between posterior lateral margin of prostomium and peristomium, cilia not observed. Peristomium a lobed ring surrounding prostomium dorsally and laterally ( Fig. 7A ), ventrally surrounding mouth as single anterior ridge and about eight elongate ventral and lateral lobes; proboscis a relatively smooth sac everted on both paratypes ( Fig. 7A ).

Parapodia with short conical lobes on setigers 1–13, from setiger 14 lobes becoming longer, developing prominent dorsal and ventral cirri ( Fig. 8B ); dorsal cirri directed dorsolateral, asymmetrical, triangular-shaped, terminating with short rounded tip ( Fig. 8C ); ventral cirri directed ventrolateral, asymmetrical with broad basal attachment and short nipple-like tip ( Fig. 8D ); both dorsal and ventral cirri with darkly pigmented tubular glands directed towards tips ( Fig. 8C, D ); ciliated rounded button-like interramal papilla present ( Fig. 8E ).

Heavy curved acicular spines present in both noto- and neuropodia of setigers 1‒3 and a few in notopodia of setiger 4; notopodia of setigers 1–2 with 8–9 spines in first and second rows and 2–3 long capillaries in second row, setiger 3 with 5–7 spines in first row and all capillaries in second row, setiger 4 with a few narrow spines with capillaries in first row and all capillaries in second row. Neuropodia of setigers 1–2 with 5‒7 spines in anterior and posterior rows, accompanied by a few capillaries in second row; setiger 3 with 3–4 spines in first row and all capillaries in second row. Setiger 4 with all capillaries in two rows. Individual spines curved, narrowing to pointed tip or more elongated capillary tip; shaft of spines hirsute with numerous fibrils present along shaft ( Fig. 7C, D ). Short spinous setae anterior to heavy spines present on notopodia of setigers 2–3. Furcate setae short, first present on setiger 4 or 5 anterior to long capillaries; furcate setae of posterior setigers longer, spine-like, more numerous with ten or more per noto- and neuropodia. Furcate setae with long unequal tynes bearing short bristles between tynes ( Figs 7E , 8F ).

Pygidium with terminal anus surrounded by about 12 lobes; four short anal cirri present ( Fig. 7B ).

Remarks. By having a few anterior acicular spines on setiger 4, and all spines of setigers 1–4 hirsute, Oligobregma bathyala sp. nov. has some similarity to O. brasierae Wiklund et al., 2019 from the Clarion Clipperton Zone (CCZ), which also has acicular spines on setigers 1–4. The two species while both occurring in deep-water Pacific habitats, differ in the following respects. Oligobregma bathyala sp. nov. has short, rounded frontal horns that are subterminal and directed anteriorly, the posterior noto- and neuropodial cirri are broad basally, asymmetrical, and bear internal tubular glands, and the peristomium consists of a single ring with several dorsal and lateral lobes. In contrast, O. brasierae has large rounded frontal horns that are located anterolateral on the prostomium, the posterior noto- and neuropodial cirri are more erect and not asymmetrical and bear internal glands that are not tubular, and the peristomium is a single smooth ring without lobes.

The only previously described species of Oligobregma reported with tubular-shaped glands in the noto- and neuropodial cirri is O. mucronata Blake, 2015 from the east Antarctic Peninsula. However, O. mucronata has acicular spines limited to setigers 1–3 instead of 1–4; the posterior cirri are more erect, not as asymmetrical, and have more of the tubular glands than O. bathyala sp. nov. In addition, the acicular spines of O. mucronata are distinctly aristate instead of a mix of spines having pointed to long, capillary tips.

Biology. A few isolated eggs measuring 95–100 µm in diameter are present in the holotype and one paratype ( AM W.52699) .

Etymology. The epithet is from the Greek, bathys for deep.

Distribution. Lower continental slope off SE Australia, 2694–2774 m.

Figures

Figure 7. Oligobregma bathyala sp. nov. (A) anterior end, dorsal view; (B) posterior end, dorsal view; (C) notopodial acicular spines, setiger 2; (D) neuropodial acicular spines, setiger 2; (E) furcate seta. A, C, D, paratype (AM W.52688); B, E, paratype (AM W.52687).

Figure 8. Oligobregma bathyala sp. nov. (A) entire worm, dorsal view (from life); (B) parapodium setiger 17, anterior view; (C) dorsal cirrus, setiger 17; (D) ventral cirrus, setiger 17; (E) interramal papilla from setiger 17; (F) furcate seta, setiger 17. A, holotype (AM W.52686); B–F, paratype (AM W.52687). A, in life photo taken at sea by Ms Karen Gowlett-Holmes.