Oligobregma profunda, 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 : 287-290

Oligobregma profunda sp. nov.

urn:lsid:zoobank.org:act:B9DFDE17-E4E4-4D49-AFEC-6F859216F187

Figs 9–10

Holotype: abyssal plain off eastern Australia, New South Wales, Hunter Marine Park, RV Investigator, Sta. 079, coll. 04 June 2017, Brenke sledge, 32.527°S 153.898°E to 30.163°S 153.524°E, 4031 m ( AM W.53992). Paratypes (131): same data as holotype (40, W.52698);—off Tasmania, Freycinet Marine Park, Sta. 009, coll. 19 May 2017, Brenke Sledge, distance 4.2 km, 41.626°S 149.560°E, to 41.662°S 149.149°E, 4021–4035 m (1, W.52678; 4, W.52680);— between Victoria and Tasmania, Flinders Marine Park, Sta. 016, coll. 21 May 2017, Brenke Sledge, distance 4.3 km, 40.463°S 149.415°E, to 40.461°S 149.364°E, 4129–4131 m (13 W. 52685);—between Victoria and Tasmania, Bass Strait Marine Park, RV Investigator, Sta. 031, coll. 23 May 2017, Brenke sledge, 39.422°S 149.604°E to 39.391°S 149.597°E, 4150–4170 m (3, W.52690; 57, W.56291; 3, W.56292; 2, W.56293);—off SE Victoria, East Gippsland Marine Park, RV Investigator, Sta. 33, coll. 24 May 2017, Brenke sledge, 38.521°S 150.213°E to 38.498°S 150.207°E, 4107– 4064 m (1, W.52694);—off SE New South Wales, Jervis Marine Park, RV Investigator, Sta. 54, 28 May 7 2017, Brenke Sledge, 38.117°S 151.473°E to 35.099°S 151.455°E, 4026– 3881 m (7, W.53993). All in the Australian Museum.

Description. Holotype complete with 27 setigerous segments, 10.5 mm long, 0.35 mm wide across prostomium, 0.6 mm wide across setiger 1, and 1.45 mm wide across expanded setigers; complete paratype with 29 setigers (AM W.53992), 11.9 mm long, 1.0 mm wide across anterior setigers and 2 mm wide across expanded middle setigers. Body narrow over first four setigers ( Figs 9A , 10A ), then expanded through next 6–8 setigers, thereafter abruptly narrowing to posterior end ( Fig. 10A ), but sometimes with a few far posterior setigers again becoming expanded. Colour in alcohol opaque white, without body pigment.

Body segments with transverse annular rows of weakly raised pads; all setigers from 2–5 with 3–4 annular rings, best observed in middle and posterior segments ( Fig. 10B ); setigers 1–3 and swollen segments with annular rings and raised pads not readily apparent. Venter with prominent ventral raised midline from setiger 1 continuing along entire body; this ridge appearing lumpy where it crosses over annular rings. Branchiae absent. Pygidium of holotype elongate with four short anal cirri and six short lobes surrounding anal opening ( Fig. 9C ).

Prostomium broadly curved across anterior margin, weakly expanded laterally, V-shaped dorsally, narrowing posteriorly, interrupting peristomial rings and extending onto dorsal surface of setiger 1 ( Fig. 9A ); with two short, rounded lobes emerging subapically from anterior margin and extending forward forming short frontal horns ( Figs 9A , 10B ); horns sometimes merged with lateral anterior prostomial margins; eyes absent; nuchal organs narrow slits along posterior margins anterior to peristomium. Peristomium a double-lobed ring surrounding prostomium dorsally and laterally, ventrally surrounding mouth with circle of raised lobes ( Fig. 9B ). Short proboscis everted on some specimens, each with numerous papillae on anterior end.

Parapodia with short, conical-shaped podial lobes in anterior third of body, becoming longer posteriorly; dorsal and ventral cirri present from setiger 14 on holotype, these podial lobes inconspicuous anteriorly, becoming longer and more prominent posteriorly ( Fig. 10A, B ); dorsal cirri triangular, broad, basally tapering to narrow pointed tip ( Fig. 10C ); ventral cirri asymmetrical, with broad basal attachment narrowing to rounded tip ( Fig. 10C ); dorsal cirri more erect than ventral cirri; both dorsal and ventral cirri with a few internal tubular-shaped glands extending toward nipple-like tips; button-like interramal papilla present ( Fig. 10C ), cilia not observed.

Heavy curved acicular spines present in both noto- and neuropodia of setigers 1‒3 ( Fig. 9A ); notopodia of setigers 1–2 with 6–8 spines in first row and long capillaries in second row, setiger 3 with 3–4 spines in first row and capillaries in second row; largest specimens sometimes with 1–2 spines also in second row of setiger 1. Neuropodia with 3‒5 spines in anterior row in setigers 1‒2, accompanied by posterior row of capillaries; setiger 3 with 0–3 spines in first row and capillaries in second row. Individual spines curved, narrowing to pointed tip ( Figs 9D–E , 10D ). Notopodial spines more robust than those of neuropodia. Short spinous setae anterior to heavy spines or capillaries present or absent, if present only on neuropodia of setigers 3–4. Furcate setae short, first present from setiger 5 or 6 anterior to long capillaries in both noto- and neuropodia; furcate setae of posterior setigers longer, spine-like. Both short and long furcate setae with long unequal tynes bearing short bristles between tynes ( Figs 9F , 10E ); these numbering 3‒4 per noto- and neuropodium in anterior segments and 8‒10 or more in posterior most segments.

Remarks. Oligobregma profunda sp. nov., with anterior acicular spines in both rami of setigers 1–3, is most similar to O. aristata sp. nov., O. mucronata , and O. tasmania n. comb. All are from the southern hemisphere and most from deep water. Of these, O. aristata sp. nov. and O. mucronata have acicular spines with aristate tips, whereas O. profunda sp. nov. and O. tasmania n. comb. have spines with blunt or pointed, not aristate, tips. Oligobregma tasmania n. comb. is an abyssal species known only from its original account ( Kirkegaard, 1996) and several important characters were not mentioned or well-illustrated. However, Kirkegaard (1996: fig. 6a) suggests that the posterior dorsal cirri are low, not erect or prominent and the prostomium as figured suggests that two short lateral horns arise from a narrow prostomial lobe ( Kirkegaard, 1996: fig. 6b). In contrast, the dorsal and ventral cirri of O. profunda sp. nov. are prominent triangular-shaped cirri that taper to a pointed tip and the prostomium has two short, rounded frontal horns arising from a broadly curved anterior margin.

Little molecular data is available for species of Oligobregma . However, COI sequences were successful for O. profunda sp. nov. and diverged about 9% from O. brasierae and O. tanai , two abyssal species from the CCZ. As presented in Table 2 , species of Oligobregma may be divided into three groups based on the number of anterior setigers having acicular spines. The two CCZ species have acicular spines on setigers 1–4, whereas O. profunda sp. nov. has acicular spines on setigers 1–3.

GenBank Accession Number. COI: OP572114.

Etymology. The epithet is from profundus, Latin for deep in reference to the deep-sea habitat of this species.

Distribution. Abyssal depths off easternAustralia, Tasmania to New South Wales, 3881‒4170 m.

Figures

Figure 9. Oligobregma profunda sp. nov. (A) anterior end, dorsal view; (B) anterior end, ventral view; (C) posterior end, dorsal view; (D–E) notopodial acicular spines, setiger 2; (F) furcate seta. A, C holotype (AM W.53992); B, paratype (AM W.52691); D–F, paratype (AM W.52698).

Figure 10. Oligobregma profunda sp. nov. (A) Entire worm, dorsal view (from life); (B) anterior half, dorsal view; (C) posterior parapodium, setiger 21, anterior view; (D) acicular spines, setiger 2; (E) furcate setae.A, C, E, holotype (AM W.53992); B–D, paratype (AM W.52698). B, C, stained with Shirlastain A; A, in life photo taken at sea by Ms Karen Gowlett-Holmes.