Aphelochaeta jubata, 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 : 251

Aphelochaeta jubata sp. nov.

urn:lsid:zoobank.org:act:E7FF22A4-2129-488B-8015-DD316AF3B99F

Fig. 1

Holotype: Abyssal plain off eastern Australia, between Victoria and Tasmania , Flinders Marine Park , RV Investigator, Sta. 016, coll. 21 May 2017, Brenke sledge, 40.463°S 149.415°E to 40.461°S 149.364°E, 4131 m (Australian Museum W.52706 ) . Paratypes (3): 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 (1, AM W.53523; 1, W.52716 ; 1, W.52328 ) .

Description. All specimens incomplete: holotype (AM W.52706) with 61 setigers, 8.9 mm long, 0.61 mm wide across peristomium, 0.72 mm wide across setiger 8; paratype (AM W.52716) a mature female, with 39 setigers, 5.8 mm long, 0.3 mm wide across anterior setigers; with eggs measuring 120–200 µm in longest diameter. Ventral ridge present from setiger 1 ( Fig. 1B ), continuing along anterior and middle segments; in middle segments ridge becomes expanded medially at each segmental junction. Dorsal grooves and ridges absent. Colour in alcohol, light tan with no additional pigment.

Pre-setiger region elongate, thickened, about as long as first eight setigers ( Fig. 1A–B ). Prostomium triangular, tapering to narrow rounded tip ( Fig. 1A–C ); eyespots absent; nuchal organs narrow slits on posterior lateral margins ( Fig. 1C ). Peristomium elongate, with three annular rings interrupted dorsally by prominent dorsal crest ( Fig. 1A ); ventrally only first ring apparent, rest of venter relatively smooth, with a low ridge transitioning to a distinct ventral ridge from setiger 1 continuing along body ( Fig 1B ). Mouth with several rounded lobes inside posterior lip ( Fig. 1B ). Dorsal tentacles arise from posterior margin of third peristomial ring; first pair of branchiae lateral to dorsal tentacles ( Fig. 1A, C ); second pair of branchiae on setiger 1 dorsal to notosetae; subsequent branchiae in a similar position. Most branchiae missing or broken, represented by scars or stubs.

Parapodia of first 7–8 setigers slightly elevated producing shoulders; noto- and neuropodia rounded lateral lobes from which fascicles of capillary setae arise ( Fig. 1C ); thereafter podial lobes reduced, but still visible until about setiger 30 ( Fig. 1D ) after which setae appear to arise directly from body wall. Post- and pre-setal lobes or lamellae entirely absent. Setae all smooth capillaries, non-limbate or granulated; fimbriated borders not observed at 1000 ×. Anterior setigers with 6–9 capillaries in anterior notopodia and 5–6 in neuropodia; middle body setigers with about five notosetae and 3–4 neurosetae.

Nature of posterior end and pygidium unknown.

Methyl Green staining. Stain concentrates in the ventral intersegmental grooves on anterior and middle setigers producing a distinct band that extends from the base of each parapodium down and around each segment being interrupted mid-ventrally by the longitudinal groove. There are no other areas of the body that retain stain. The stain is very evident on the specimens from Sta. 016 (including holotype), but weaker on the specimens from Sta. 31.

Remarks. Among species of Aphelochaeta described from abyssal depths, A. jubata sp. nov. is most similar to Aphelochaeta clarionensis Blake, 2019 from the abyssal depths of the Clarion-Clipperton Fracture Zone in the Pacific Ocean, in having the peristomial rings interrupted by a dorsal crest. However, A. clarionensis has only two peristomial rings instead of three in A. jubata sp. nov. In addition, the MG staining patterns of the two species differ in that A. clarionensis has a distinct pattern on the pre-setiger region and no pattern on the body segments. In contrast, A. jubata sp. nov. has no pre-setiger staining pattern, but stain is retained as intersegmental bands on anterior and middle segments.

Another abyssal species of Aphelochaeta with a distinct dorsal peristomial crest is Aphelochaeta brandtae Blake, 2018 from the Southern Ocean and Weddell Sea, Antarctica. However, in contrast to A. jubata sp. nov., A. brandtae has two peristomial rings instead of three, and a prominent MG pattern on the pre-setiger region and broad bands across the venter of anterior segments instead of no pre-setiger pattern and the stain retained on anterior and middle segments is concentrated in the narrow intersegmental grooves.

Etymology. The epithet is from the Latin, juba for mane or crest, in reference to the distinctive dorsal crest found on the peristomium of this species.

Distribution. Abyssal plain between Victoria and Tasmania, eastern Australia, 4031–4170 m.

Figures

Figure 1. Aphelochaeta jubata sp. nov. (A–B) holotype (AM W.52706): (A) anterior end, dorsal view; (B) anterior end, ventral view. (C–D) paratype (AM W.53523): anterior end, left lateral view; (D) abdominal parapodium, anterior view.