Chaetocirratulus glebalis, Blake, 2023

Blake, James A., 2023, New Species of Cirratulidae (Annelida) from Continental Slope and Abyssal Depths off Eastern Australia, Records of the Australian Museum (Rec. Aust. Mus.) 75 (3), pp. 249-270 : 257

Chaetocirratulus glebalis sp. nov.

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Figs 5–6

Holotype: Abyssal plain off eastern Australia, 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, 4170 m ( AM W.53524) . Paratypes (3): same data as holotype (3, AM W.53525) .

Description. All specimens incomplete, including four anterior fragments and one posterior fragment. Holotype largest specimen, with 60 setigers, 10.6 mm long, 0.9 mm wide across anterior setigers; largest paratype with 25 setigers, 3.0 mm long, 1.0 wide. Body with thick, crowded segments along entire body ( Figs 5A–B , 6C–E ); individual segments up to ten times wider than long.Anterior segments with transverse lumpy dorsal ridge ( Fig. 5A ), but without longitudinal grooves or ridges; venter with prominent mid-ventral ridge along entire body composed of broad medial bulge on each segment ( Figs 5B , 6B ), connected mid-ventrally at intersegmental groove. One paratype a mature female with large eggs in two swollen posteriormost setigers of fragment ( Fig. 6C–D ). Eggs 160–200 µm in longest diameter. Colour in alcohol tan without any obvious pigment.

Pre-setiger region broad, thickened, with prostomium curved ventrally, not visible in dorsal view ( Fig. 5A–B ). Prostomium a short, pear-shaped lobe, broadly rounded across anterior margin ( Figs 5B , 6B ); eyespots absent; nuchal organs curved grooves on lateral margins ( Fig. 5B ). Peristomium with two irregularly-shaped rings, each with unique morphology: (1) anteriormost ring bulbous, encircling prostomium and mouth ( Fig. 5B ), bearing fan-shaped dorsal crest ( Figs 5A , 6A, C ); (2) second ring consisting of an irregular series of lobes that overall merge with setiger 1; mid-dorsal lobe swollen, with a pair of grooves on anterior margin with notch containing scar representing origin of dorsal tentacles ( Fig. 5A ); ventral side with broad semi-circular crest extending posteriorly over setigers 1–2 ( Fig. 5B ).

Parapodia of anterior setigers elongate rounded lateral lobes from which setae emerge; reduced to narrow ridge in middle and posterior setigers ( Fig. 5C ); pre- and post-setal lobes entirely absent. Branchiae from setiger 1, dorsal to notosetae, continuing to at least mid-body; branchiae mostly missing, but represented by scars and stubs. Noto- and neurosetae include long thin capillaries throughout, including a few long natatory-like setae ( Fig. 6C ) and few narrow acicular spines in far posterior setigers ( Fig. 5C ). Capillaries of anterior setigers numbering 6–8 in notopodia and 9–10 in neuropodia; middle setigers with 7–9 capillaries in notopodia and 8–10 in neuropodia. Acicular spines not present in short paratypes, but present from about setiger 55 in holotype, with 2–3 spines in neuropodia and 0–1 in notopodia. Posterior fragment with pre-pygidial segments with up to six spines in neuropodia and 2–3 in notopodia ( Fig. 5C ). Individual spines narrow, weakly curved, tapering to narrow rounded tip ( Fig. 5D ).

Posterior fragment narrowing to short conical pygidial lobe.

Methyl Green staining. No general pattern, however intersegmental grooves retain stain to varying degrees ( Fig. 6D–E, arrows), with dorsal surface of some middle and posterior segments staining lightly.

Remarks. Chaetocirratulus glebalis sp. nov. is an entirely unique cirratulid in the nature of the numerous lobes and lumps on the pre-setiger region and on the body segments. The species is referred to Chaetocirratulus because of the relatively thickened body, short anteriorly rounded pre-setiger region and hidden nature of the prostomium. I know of no other cirratulids from deep water or shallower depths with a similar appearance. The morphology and arrangement of the acicular spines is, however, similar to some species of Chaetozone , except that posterior segments do not have cinctures and the spines are not large nor sigmoid in shape.

Biology. The large protruding eggs (160–200 µm) on the paratype suggest direct or lecithotrophic development, which would be expected for an abyssal species. However, long natatory-like capillaries might suggest a mechanism for movement at the sediment-water interface at the time of spawning. The short, blunted pre-setiger region suggests that the species burrows by pushing particles out the way and opening cracks in the sediment rather than moving between particles.

Etymology. The epithet is from the Latin, gleba for lump, in reference to the lumpy segmental appearance of the body of this species.

Distribution. Abyssal plain between Victoria and Tasmania, eastern Australia, 4170 m.

Figures

Figure 5. Chaetocirratulus glebalis sp. nov. (A–B) holotype (AM W.53524): (A) anterior end, dorsal view; (B) anterior end, ventral view. (C–D) paratype (AM W.53525): (C) posterior setiger, anterior view; (D) posterior neuroacicular spines.

Figure 6. Chaetocirratulus glebalis sp. nov. Photomicrographs (A, C–D) paratype (AM W.53525); (B, E) holotype (AM W.53524). (A) anterior end, right lateral view; (B) anterior end, ventral view; (C) entire fragment, dorsal view; (D) same, left lateral view; (E) posterior segments, dorsal view. A–C, stained with Shirlastain A; D–E, stained with Methyl Green.