Oligobregma aristata, 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

Oligobregma aristata sp. nov.

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Figs 5–6

Holotype: abyssal plain off New South Wales, eastern Australia, 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, Sta. 079 ( AM W.53900) . Paratype (1): lower continental slope off Tasmania, eastern Australia, Freycinet Marine Park , RV Investigator, Sta. 11, coll. 19 May 2017, box core, 41.721°S 149.125°E, 2793 m ( AM W.52683) .

Description. Holotype mostly complete, missing pygidial segment, with 23 setigers, 13.6 mm long, 1.3 mm wide across first four anterior setigers, 2.32 mm wide across expanded middle setigers. Paratype smaller but incomplete, with middle segments removed for DNA analysis. Setigers 1–4 narrow ( Fig. 5A, B ), body expanded from setigers 5–10 then narrowing to posterior end. Body with transverse rows of raised pads best observed on setigers 1–4 ( Fig. 5A, B ) and 11–22; pads in 4–5 rows on expanded middle segments, but obscured by stretching, best seen ventrally. Dorsally, setiger 1 with a single enlarged medial dorsal pad; setiger 2 with a row of large pads; setigers 3–4 with three transverse rows of pads ( Fig. 5A ); setigers 11–22 with 3–4 narrow transverse rows of pads. Ventrally with a single transverse pad on setiger 1, setigers 2–3 with three rows of pads; setiger 4 with two rows of pads ( Fig. 5B ); prominent mid-ventral ridge extending from setiger 1 to end; ridge interrupts transverse rows of pads at each segmental boundary ( Fig. 5B ). Branchiae absent; posterior end not present on either specimen. Colour in alcohol, opaque white.

Prostomium broadly curved across anterior margin, weakly expanded laterally, dorsally narrowing posteriorly producing V-shape ( Fig. 5A ); merging with narrow peristomium; with two short, rounded lobes emerging subapically from anterior margin and extending forward forming a pair of short frontal horns ( Fig. 5A, B ), both horns with groove or notch producing weak bilobed appearance ( Fig. 5A, B ); eyes absent; nuchal organs visible as numerous fine cilia between posterior lateral margin of prostomium and narrow peristomial ring. Peristomium a single ring ( Fig. 5A ), dorsally merging with posterior margin of prostomium and ventrally forming lips of mouth with two anterior lobes, two lateral lobes, and about eight short narrow posterior lobes or papillae ( Fig. 5B ).

Parapodia with short, conical-shaped podial lobes from setigers 1–10, from setiger 11 lobes becoming longer, developing prominent dorsal and ventral cirri ( Fig. 6A ); dorsal cirri broad, globular, tapering to nipple-like rounded tip directed dorsally ( Fig. 6B ); ventral cirri asymmetrical with broad basal attachment bearing anteriorly directed nipple-like tip ( Fig. 6C ); both dorsal and ventral cirri with lattice-like glandular cells encompassing entire cirrus and nipple-like tips; rounded button-like interramal papilla present ( Fig. 6A ), cilia not observed.

Heavy curved acicular spines present in both noto- and neuropodia of setigers 1‒3 ( Fig. 5A, B ); notopodia of setigers 1–2 with 4–5 spines in first and second rows and 2–3 long capillaries in second row, setiger 3 with 3–4 spines in first row and all capillaries in second row. Neuropodia of setigers 1–2 with 3‒4 spines in anterior and posterior rows, accompanied by a few capillaries; setiger 3 with 3–4 spines in first row and all capillaries in second row. Setiger 4 with all capillaries in two rows of both noto- and neuropodia. Individual spines curved, narrowing to pointed tip bearing distinct arista ( Figs 5C, D , 6D ). Short spinous setae anterior to heavy spines or capillaries absent. Furcate setae short, first present from setiger 5 anterior to long capillaries; furcate setae of posterior setigers longer, spine-like, more numerous, ten or more per noto- and neuropodium ( Fig. 6A ). Furcate setae with long unequal tynes bearing short bristles tween tynes ( Figs 5A , 6E ).

Remarks. Oligobregma aristata sp. nov. differs from other species off eastern Australia in having anterior acicular spines with an aristate-like tip. In addition, the short frontal horns of the holotype are distinctly notched or weakly bifid and the dorsal and ventral cirri of posterior parapodia are inflated and have nipple-like tips. Such frontal horns and dorsal and ventral cirri have not been observed previously in other scalibregmatids. The only other species of Oligobregma reported with aristate acicular spines is O. mucronata Blake, 2015 from the East Antarctic Peninsula in upper slope or bathyal depths less than 1000 m. However, O. mucronata has triangular-shaped dorsal and ventral cirri that taper to pointed tips instead of swollen asymmetrical cirri with nipple-like tips.

Etymology. The epithet is from arista, Latin for long pointed awn (of grasses) or ear; in reference to the pointed tip of the acicular spines of this species.

Distribution. Off eastern Australia lower continental slope and abyssal depths, 2793–4031 m.

Figures

Figure 5. Oligobregma aristata sp. nov. Holotype (AM W.53990): (A) anterior end, dorsal view; (B) anterior end, ventral view; (C) notopodial acicular spines, setiger 1; (D) notopodial acicular spines, setiger 2; (E) furcate seta, setiger 19.

Figure 6. Oligobregma aristata sp. nov. Holotype (AM W.53990): (A) parapodium, setiger 19, anterior view; (B) dorsal cirrus, setiger 19; (C) ventral cirrus, setiger 19; (D) notopodial acicular spine, setiger 2; (E) furcate seta, setiger 19. A–D, stained with Shirlastain A.