Chaetocirratulus pinguis Hartman 1978, new combination

Chaetocirratulus pinguis Hartman, 1978, new combination

Figure 36

Chaetozone pinguis Hartman, 1978:166, fig. 18a–c; Usha et al. 2014: 917.

Cirratulus patagonicus: Hartman 1978: 166. Not Kinberg 1866.

Material examined. Weddell Sea, USCG Glacier Sta. 69-1, 24 Feb. 1969, 74°28.1ʹS, 30°31.7ʹW, 513 m, holotype (USNM 46782) and 13 paratypes (USNM 46783); Sta. 68-5, 9 Feb 1968, 76°00ʹS, 55°00ʹW, 400 (1, USNM 46800); Sta. 69-7, coll. 01 March 1969, 77°16ʹS, 42°38ʹW, 512 m, (1, USNM 490733); Weddell Sea, east of former Larsen Ice Shelf A Area, RVIB Nathaniel B. Palmer Cr. 2000-03, coll. J.A. Blake, Sta. 26, 23 May 2000. 64°39.564ʹS, 059°13.226ʹW, SM grab, 564 m (1, MCZ 149836).— East Antarctic Peninsula, Prince Gustav Channel, RVIB Nathaniel B. Palmer Cr. 2000-03, coll. J.A. Blake, SM grab, Sta. 01, 14 May 2000, 64°17.625´S, 058°34.678´W. 768 m (1, JAB); Sta. 34, 24 May 2000, 64°10.995ʹS, 058°34.140ʹW, 865 m (5, MCZ 149837; 1 SEM stub, JAB); N of Larsen Ice Shelf Area A, off Lindenberg Island , RVIB Nathaniel B. Palmer Cr. 2000-03, coll. J.A. Blake, SM grab, Sta. 03, 15 May 2000, 64°53.533ʹS, 059°30.694ʹW, 385m (1, MCZ 149838); former Ice Shelf A Area, Greenpeace Trough, RVIB Nathaniel B. Palmer Cr. 2000-03, coll. J.A. Blake, SM grab, Sta. 22, 20 May 2000, 64°46.632ʹS, 060°21.557ʹW, 868 m (1, LACM-AHF Poly 10214); Sta. 12, 19 May 2000, 64°55.101ʹS, 060°24.459ʹW, 317 m (1, LACM-AHF Poly 10215); former Ice Shelf A Area, border with Larsen B , RVIB Nathaniel B. Palmer Cr. 2000-03, coll. J.A. Blake, SM grab, Sta. 13, 19 May 2000, 64°53.517ʹS, 060°28.836ʹW, 323 m (1, LACM-AHF Poly 10216); Sta. 14, 19 May 2000, 64°51.818ʹS, 060°33.438ʹW, 419 m (4, LACM-AHF Poly 10217).— South Shetland Islands, Clarence Island , USNS Eltanin, Cr. 12, Sta. 1089, 17 Apr 64, 60.78°S, 53.507°W, Blake trawl, 641 m (1, USNM 1013943).— Ross Sea, Pennell Bank, off Ross Ice shelf, ca. 385 km W of McMurdo Station, USNS Eltanin Cr. 32, Sta. 2060, 25 Jan 1968, 77.98°S, 178.18°E, Camera grab, 647 m (1, USNM 1490734).

Description. A small species, specimen from USNS Eltanin Sta. 1089 (USNM 1013943) 6 mm long and 5.2 mm wide for 48 setigerous segments; types smaller, up to 4.2 mm long for 30 segments. Body distinctly fusiform in shape in types (Fig 36A) and some non-types; juveniles more elongate, thick, tapering posteriorly, thickened in middle, but not distinctly fusiform. Individual segments biannulate (Fig. 36B). Shallow mid-dorsal groove apparent in some specimens (Fig. 36A). Color tan, with no additional pigmentation.

Prostomium broadly rounded on anterior margin, subtriangular in shape, wider than long (Fig. 36 A–B). Peristomium well developed, dorsally overlapping first segment somewhat, with deep lateral grooves forming

three weakly developed annular rings, well developed laterally (Fig. 36B); dorsum of peristomium relatively smooth, without dorsal crest (Fig. 36A). Dorsal tentacles medial in location, arising from groove between peristomium and setiger 1 (Fig. 36 A–B) or anterior margin of first setiger; tentacles thick, short in preservation. First pair of branchiae arising lateral to dorsal tentacles in same groove between peristomium and setiger 1 (Fig. 36 A–B); subsequent branchiae arising dorsal to setal fascicles (Fig. 36B), continuing through first half of body.

Capillary setae in noto- and neuropodia throughout; acicular spines in notopodia from middle and posterior setigers and in neuropodia from setiger 1–5. Acicular spines short, straight (Fig. 36 D–E); capillaries sometimes with finely serrated or fringed border (Fig. 36E, inset).

Pygidium terminating a conical lobe ventral to anal opening (Fig. 36A).

Methyl Green stain. The prostomium stains lightly; the peristomium stains heavily, especially on the sides; the body segments are generally unstained.

Remarks. Chaetocirratulus pinguis is similar to C. andersenensis in that most specimens have a robust, fusiform body. The two species differ in that the first has acicular spines present in the neuropodia from anterior setigers 1–5 instead of a far posterior setiger. Chaetocirratulus andersenensis has acicular spines limited to a few posterior neuropodia, rarely in notopodia; whereas in A. pinguis, acicular spines are present in both noto- and neuropodia throughout. In addition, the three peristomial rings are typically prominent and well-defined in C. andersenensis, but only weakly developed in C. pinguis, giving the pre-setigerous region a smooth appearance.

Habitat. Chaetocirratulus pinguis was noticeably abundant in the vicinity of the former Larsen Ice Shelf A where the surficial sediments (0–5 cm) consist of 0–40% sand likely derived from the formerly overlying ice cover (Gilbert & Domack 2003).

Distribution. Weddell Sea and Antarctic Peninsula in shelf and upper slope depths, 317–865 m; East Antarctica, 203 m.