Chaetocirratulus bathyalis, 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 : 255

Chaetocirratulus bathyalis sp. nov.

urn:lsid:zoobank.org:act:518D66CF-5EEA-4503-8069-A59E1D9BDC8B

Fig. 4

Holotype. Continental slope off eastern Australia, Central Eastern Marine Park, W of Coffs Harbor, NSW, RV Investigator, Sta. 087, coll. 06 June 2017, Brenke sledge, start 30.113°S 153.898°E, 2634 m to 30.116°S 153.867°E, 2324 m ( AM W.52713).

Description.A small species, holotype complete, with about 65 setigers, 13.1 mm long, 1.1 mm wide across anterior setigers and about 1.2 mm wide across middle setigers, narrowing posteriorly. Body elongate, thick, grub-like, but not fusiform; segments short, wide, anterior segments about 4.5 times wider than long ( Fig. 4A ); posterior segments about six times wider than long ( Fig. 4C ). In cross section, body segments dorsoventrally flattened, but with dorsum and venter rounded; with ventral ridge extending from peristomium continuing along entire body; dorsal ridge or groove absent. Individual segments all uniannulate, but middle and posterior segments crossed with numerous thin wrinkles. Colour in alcohol: light tan.

Pre-setiger region about as wide as long, as long first five setigers ( Fig. 4A ). Prostomium wedge-shaped in dorsal and ventral view, narrowing to rounded tip ( Fig. 4A–B ); with rounded, bulbous shape in lateral view; eyespots absent; nuchal organs large, crescent-shaped grooves on posterior lateral margin. Peristomium with lateral and ventral grooves producing three rings ( Fig. 4A ), a narrow anterior ring followed by two more-or-less equal larger rings; surmounted by irregular shaped dorsal crest not crossed by peristomial grooves ( Fig. 4A ). Ventrally, peristomial rings only weakly apparent; mouth opening encompassed by first ring, with upper lip formed by about six lobes ( Fig. 4B ). Dorsal tentacles arise from a narrow groove between third peristomial ring and setiger 1, possibly an achaetous segment ( Fig. 4A ). First pair of branchiae lateral to dorsal tentacles in same groove. Subsequent branchiae arise dorsal to notosetae from setiger 1, continuing on subsequent setigers ( Fig. 4B ). Most branchiae missing or reduced to stubs or scars.

Parapodia reduced to ridge from which noto- and neurosetae arise ( Fig. 4D ); podial lobes entirely absent. Noto- and neurosetae include acicular spines and long, thin capillaries.Acicular spines arise from setiger 1 in both noto- and neuropodia. Notosetae include 3–4 acicular spines and at least one long capillary in anterior setigers ( Fig. 4D ), reduced to 1–2 spines and one long capillary in middle and posterior setigers. Neurosetae include 4–5 acicular spines and at least one long capillary in anterior setigers ( Fig. 4D ), reduced to 2–3 spines and one long capillary posteriorly. Notoacicular setae generally with weakly curved shafts narrowing to rounded tip ( Fig. 4E ); neuroacicular setae with slightly thicker, straight shaft and rounded tips ( Fig. 4F ). Capillaries of anterior setigers narrow, whip-like, becoming thicker and stiff posteriorly. Majority of setae broken off in holotype.

Posterior end narrowing to short pygidium with cap-like rounded lobe ( Fig. 4C ).

Methyl green staining. Individual gland cells staining all along body, producing bands of speckles over individual segments; dense concentrations of speckles on peristomium especially last ring and dorsal crest.

Remarks. Chaetocirratulus bathyalis sp. nov. is similar to Chaetocirratulus pinguis ( Hartman, 1978) from Antarctica in having noto- and neuropodial spines from setiger 1. The two species differ in that C. pinguis has a distinctly fusiform body, three weakly developed peristomial rings with no dorsal crest, a shallow mid-dorsal groove along the body but no ventral ridge, and individual segments that are distinctly biannulate ( Blake, 2018). In contrast, C. bathyalis sp. nov. has a thickened but not fusiform body, at least two well-developed peristomial rings and a prominent dorsal crest, no mid-dorsal groove but a distinct ventral ridge, and uniannulate segments with numerous transverse wrinkles. In addition, the MG staining pattern differs between the two species: in C. pinguis the retained stain is largely limited to the pre-setiger region where the prostomium stains lightly and the peristomium stains heavily, especially laterally. In contrast, C. bathyalis sp. nov. has stain concentrated in individual glands, producing bands of speckles all along the body and dense concentrations of speckles on the last peristomial ring and dorsal crest.

Etymology. The epithet is from the Greek, bathys, for deep, in reference to the deep-water habitat of this species.

Distribution. Australia, lower continental slope off New South Wales, 2324–2634 m.

Figures

Figure 4. Chaetocirratulus bathyalis sp. nov.(A–F), holotype (AM W.52713):(A) anterior end, dorsal view; (B) anterior end ventral view; (C) posterior end, dorsal view; (D) parapodium from an anterior setiger, anterior view; (E) notoacicular spines; (F) neuroacicular spines.