Chaetozone abyssalis, 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 : 260-262

Chaetozone abyssalis sp. nov.

urn:lsid:zoobank.org:act:E94E1862-60B5-476E-801C-49D11C514756

Figs 7–8

Holotype: Abyssal plain off New South Wales, eastern Australia, Hunter Marine Park, RV Investigator, Sta. 079, coll. 4 June 2017, Brenke sledge, 32.527°S 153.898°E to 30.163°S 153.524°E, 4031 m ( AM W.52712) . Paratypes (5): same data as holotype (1, W.53526);— Abyssal plain off eastern Australia, between Victoria and Tasmania , Bass Strait Marine Park, Sta. 031, coll. 23 May 2017, Brenke sledge , 39.422°S 149.604°E to 39.391°S 149.597°E, 4170 m (4, W.53528). All in Australian Museum .

Description. A small species, all specimens incomplete. Holotype a gravid female, with 24 setigers, 3.1 mm long and 0.22 mm wide across anterior setigers; paratype (AM W.53526) of a similar size, but coiled, lacking gametes ( Fig. 8C ), with 24 setigers. Body elongate, narrow, holotype with anterior 5–10 setigers narrow, c. 4.5 times wider than long ( Fig. 7A ), followed by swollen “stomach” area of about six setigers containing numerous eggs and an enlarged loop of the intestine filled with fine sediment ( Fig. 8A–B ); abdominal segments becoming moniliform, with partial cinctures developing on posterior segments of fragment. Paratype without enlarged “stomach” area but with some thickening of posterior thoracic segments filled with fine sediment particles. Dorsal and ventral crests and ridges absent. Eggs of holotype numerous, tightly packed, from about setiger 10 to 22, each egg 100–120 µm in longest diameter with conspicuous germinal vesicle. Colour in alcohol: opaque white, with no body pigment.

Pre-setiger region elongate, thick, about as long as first four setigers ( Figs 7A–B , 8A ); with expanded anterior peristomial ring surrounding narrow prostomium and mouth. Prostomium conical, tapering to rounded tip ( Figs 7A , 8A ); eyespots absent; nuchal organs present as rounded lobes on posterior lateral margins ( Fig. 7B ); ventrally prostomium forming anterior lip of mouth. Peristomium with two rings; anterior ring swollen, dorsally merging gradually with second peristomial ring ( Fig. 7A ); ventrally thickened forming posterior lip of mouth ( Fig. 7B ). Second peristomial ring relatively smooth dorsally, with low swelling mid-ventrally ( Fig. 7A–B ). Dorsal tentacles arising about two-thirds along second peristomial ring with first branchiae arising directly posterior to tentacles on posterior border ( Fig. 7A ). Second pair of branchiae on posterior border of first setiger; subsequent branchiae in similar position; most branchiae missing, represented by scars or stubs.

Parapodia reduced to low ridges or mounds from which setae arise; posterior parapodia becoming moniliform with cinctured segments developing on posteriormost segments of both specimens.Anterior setae all long capillaries numbering about 10–12 per fascicle, including long natatory-like setae in most notopodia of anterior and middle segments ( Fig. 8A–C ). Neuropodial acicular spines from setiger 22 and notopodial spines from setiger 24 on holotype. Spines numbering six in neuropodia and two in notopodia in setiger 24, or last setiger of incomplete holotype. Spines accompanied by 1–2 capillaries in neuropodia and 2–3 in notopodia. Individual spines with basal manubrium at emergence from podial lobes; spines only weakly curved, tapering to narrow pointed tip ( Fig. 7C ).

Pygidium unknown; specimens incomplete.

Methyl Green staining. Stain retained on lateral sides of peristomium, otherwise no pattern.

Remarks. Chaetozone abyssalis sp. nov. belongs to a group of deep-sea species that includes Chaetozone australosetosa Blake, 2018 and Chaetozone biannulata Blake, 2018 , both from Antarctic seas, and Chaetozone profunda Blake, 2022 from deep water in the western North Atlantic. Each of these species has two peristomial rings with the large second ring bearing dorsal tentacles well anterior to the first pair of branchiae and setiger 1, suggesting that an achaetous segment is incorporated into the peristomium. Chaetozone abyssalis sp. nov. is most similar to C. australosetosa in having a relatively thick pre-setiger region instead of one that is long, narrow, and tapering anteriorly to a pointed prostomium.

Chaetozone abyssalis sp. nov. differs from C. australosetosa in having the first peristomial ring expanded and separated from the prostomium instead of narrow and conical tapering to a prostomium that is mostly merged with it. The number of posterior spines between the two species cannot be compared due to the absence of complete specimens of C. abyssalis sp. nov.

Etymology. The epithet is from abyss, Latin for a bottomless pit or the deep sea, in reference to this species being collected from abyssal depths.

Distribution. Abyssal plain off New South Wales, eastern Australia, 4031 m.

Figures

Figure 7. Chaetozone abyssalis sp. nov. (A–C) holotype (AM W.52712): (A) anterior end, dorsal view; (B) anterior end, ventral view; (C) neuroacicular spines.

Figure 8. Chaetozone abyssalis sp. nov. Photomicrographs converted to grayscale. (A–B), holotype (AM W.52712): entire worm, dorsal view; (B) detail of enlarged “stomach” and eggs. (C) paratype (AM W.53526): entire worm, twisted in lateral view.All originally stained with Shirlastain A.