Chaetozone biannulata Blake 2018, new species

Chaetozone biannulata new species

Figures 40–41

Tharyx marioni: Hartman, 1967: 118 (in part).

Chaetozone setosa: Hartman, 1978: 166. Not Malmgren, 1867.

Chaetozone sp.: Hartman, 1978: 166 (in part).

Chaetozone sp. 1: Blake & Narayanaswamy 2004: 1806, 1813.

Chaetozone sp. 2: Blake & Narayanaswamy 2004: 1813.

Chaetozone sp. 3: Hilbig 2001: 540 (in part); Hilbig et al. 2006: 715, 717, 719, 724 (in part); Montiel et al. 2005: 197, 2016: Appendix 2 (in part).

Material Examined. Drake Passage, North of South Shetland Islands, R / V Polarstern, ANDEEP I (ANT-XIX/ 3), Sta. PS 61/114-6, 18 Feb 2002, 61°43.55ʹS, 60°43.87ʹW, box corer, 2905 m, holotype (SMF 24915) and 14 paratypes (SMF 24916); Sta. PS 61/114-5, 18 Feb 2002, 61°43.55ʹS, 60°43.87ʹW, MUC, 2917 m, 5 paratypes (SMF 24917); Sta. PS 61/114-8, 18 Feb 2002, 61°43.46ʹS, 60°43.29ʹW, box corer, 2881 m, 3 paratypes (SMF 24918); Sta. PS 61/40-4, 26 Jan 2002, 58°55.27ʹS, 61°0.02ʹW, box corer, 1838 m, 1 paratype (SMF 24919); Sta.

PS61/43-2, 29 Jan 2002, 60°26.95ʹS, 56°4.96ʹW, box corer, 3957 m, (16, SMF 24920); Drake Passage, USNS Eltanin, Cr. 4, Sta. 126, 29 Jul 1962, 57°12ʹS, 62°48ʹW, 3733–3806 m (5, USNM 56004); off King George Island, R / V Polarstern, EASIZ II (ANT-XV/3), coll. B. Hilbig, Sta. 48-334, 19 Mar 1998, 61°26.7ʹS, 58° 06.6ʹW, MG, 1028 m (1, MCZ 149850); Sta. 48-341, 19 Mar 1998, 61°34.5ʹS, 58°07.0ʹW, MG, 429 m (8, MCZ 149851).— Scotia Sea, R / V Polarstern, ANDEEP I (ANT-XIX/3), Sta. PS61/46-3, 01 Jan 2002, 60°37.92ʹS, 53°57.17ʹW, box corer, 2888 m, 6 paratypes (MCZ 24921); Sta. PS61/46-5, 01 Jan 2002, 60°38.13ʹS, 53°57.68ʹW, box corer, 2894 m (1 juvenile, SMF 24922).— Scotia Sea, Powell Basin, R / V Polarstern, ANDEEP III (ANT- XXII/3), Sta. PS67/121-12, 15 Mar 2005, 63°36.19ʹS, 50°37.15ʹW, box corer, 2657 m, (1, SMF 24923); Sta. PS67/ 142-7, 18 Mar 2005, 62°11.61ʹS, 49°29.45ʹW, box corer, 3406 m (3, SMF 24924); Sta. PS67/151-6, 21 Mar 2005, 61°45.55ʹS, 47°7.56ʹW, box corer, 1180 m, 1 paratype (SMF 24925); 1 paratype on SEM Stub (MCZ 149852); Sta. PS 67/153-5, 29 May 2005, 63°19.41ʹS, 64°36.82ʹW, MUC, 2079 m (1, SMF 24926).— Weddell Sea, off East Antarctic Peninsula, R / V Polarstern, ANDEEP II (ANT-XIX/4), Sta. PS61/131-8, 06 Mar 2002, 65°18.65ʹS, 51°30.91ʹW, box corer, 3068 m (1, SMF 24927); Sta. PS61/131-9, 06 Mar 2002, 65°18.55ʹS, 51°31.95ʹW, MUC, 3064 m, (1, SMF 24928); USCG Glacier Sta. 68-5, 09 Feb 1968, 76°00ʹS, 55°00ʹW, VV grab, 400 m, (2 complete, USNM 46784); Sta. 68-40, 03 Mar 1968, 71°47.6ʹS, 40°41.3ʹW, 2949m (1, USNM 46785); Sta. 69-21, 13 Mar 1969, 73°52ʹS, 31°, 18ʹW, 2288 m, (2, USNM 46798); Sta. 69-4, 26 Feb 1969, 77°05.5ʹS, 35°04ʹW, 743 m (1, USNM 46790).— Central Weddell Sea, R / V Polarstern, ANDEEP II (ANT-XIX/4), Sta. PS61/138-7 17 Mar 2002, 62°58.01ʹS, 27°53.87ʹW, MUC, 4541 m (1, SMF 24931).— Weddell Sea, off South Sandwich Islands, R / V Polarstern, ANDEEP II (ANT-XIX/4), Sta. PS61/141-7, 22 Mar 2002, 58°24.91ʹS, 25°1.24ʹW, box corer, 2217 m (2, SMF 24929).— South Sandwich Trench, R / V Polarstern, ANDEEP II (ANT-XIX/4), PS61/142-5, 24 Mar 2002, 58°50.83ʹS, 23°58.61ʹW, MUC, 6337 m (2, SMF 24930).— Weddell Sea, off Coats Land, USCG Glacier, Sta. 69-8, 2 Mar 1969, 77.603°S, 42.500°W, 585 m, (6 USNM 46793); Sta. 69-19, 11 Mar 1969, 74.105°S, 32.605°W, 1622 m (1); Sta. 69-20, 12 Mar 1969, 73.823°S, 31.682°W, 2288 m (1, USNM 46797).— South Shetland Islands, off King George Island, R / V Polarstern, EASIZ II (ANT-XV/3), coll. B. Hilbig, Sta. 48-326, 17 Mar 1998, 62°20.1ʹS, 58°38.8ʹW, MG, 606 m (10, SMF 24932).— West Antarctic Peninsula, Bransfield Strait, USNS Eltanin Cr. 6, Sta. 416, 02 Jan 1963, 63.67°S, 56.22°W, trawl, 494–507 m (1, USNM 1490765).— Ross Sea, E. McMurdo Sound, SW of Tent Island, Deep-Freeze II, USCG Glacier, 77°43.1ʹS, 166°21.5ʹE, OPG Grab, 421 m, coll. W.L. Tressler (1, USNM 1490766).— South Pacific Ocean, East of New Zealand, 180 km east of Antipodes Islands, USNS Eltanin Cr. 32, Sta. 2143, 26 Feb. 1968, 49.85°S, 178.583°E, Blake trawl, 2100 m (3, USNM 1490767).

Description. A moderate-sized species, holotype complete, 9.3 mm long, 0.65 mm wide across mid-body, 55 setigerous segments. Complete paratypes 9.3 to 11.8 mm long for 58–60 setigerous segments. Body with anterior segments short, about four times wider than long (Fig. 40A), becoming widest in middle body at five times wider than long, then narrowing posteriorly to moniliform segments about 1.5 times as wide as long. Wide mid-body with enlarged stomach area apparent through body wall, sometimes enlarged and apparent externally, but not distending body to any extent. Dorsal grooves and ridges absent; venter with low mid-ventral ridge present from anterior to posterior segments. Posterior segments tapered over last 15 segments, with weak groove between elevated parapodia of cinctured segments bearing spines producing prominent armature. Color in alcohol light tan, with brown pigmentation dorsolateral in segmental grooves of some specimens.

Entire pre-setiger region elongate, triangular with three parts: prostomium, peristomium, and achaetous segment merging seamlessly with setiger 1. Prostomium elongate, triangular in dorsal view, 1.5x longer than wide, tapering to narrow tip (Figs. 40A, 41 A–C); eyespots absent; nuchal organs prominent elevated lobes at posterior border with peristomium (Figs. 40A, 41 A–C), each with circular opening bearing cilia (Fig. 41A inset), not pigmented. Peristomium indistinctly separated from prostomium and separately from achaetous segment by prominent transverse groove (Figs. 40A, 41 A–C); peristomium with low dorsal crest and ventrally surrounding mouth; achaetous segment separated from peristomium by distinct dorsal groove, not continuing ventrally (Figs. 40A, 41 A–C); achaetous segment extending posteriorly, merging with setiger 1 with only evidence of separation a weak lateral groove seen in SEM (Fig. 41A); achaetous segment bearing dorsal tentacles followed by first pair of branchiae (Figs. 40A, 41 A–C). Second pair of branchiae dorsal to notosetae on setiger 1; branchiae continuing on subsequent setigers throughout body.

Anterior parapodia reduced to low elevations from which setae emerge; individual segments denoted dorsally by transverse grooves (Figs. 40A, 41C). Middle parapodia reduced to individual setal tori. Posterior setigers becoming moniliform, then transitioning to cinctured segments with elevated membranes from which spines and capillaries emerge (Figs. 40B, 41E). Anterior setae all simple capillaries; sexually mature specimens with long natatory notosetae; 10–12 notosetae and 8–10 neurosetae in thoracic setigers; reduced to 6–8 noto- and neurosetae per fascicle in far abdominal segments; notosetae longer than neurosetae; fascicles of noto- and neurosetae arising close to one another. Notoacicular spines from setigers 34–35; neuroacicular spines from setigers 37–38. In cinctured segments, up to 10–11 spines in notopodia and 10–13 spines in neuropodia, or full cinctures with 20–24 spines on a side. In cinctures, thin capillaries typically alternating with notoacicular spines in lower part of fascicle and with neuroacicular spines in upper part of fascicle (Fig. 41E). Spines curved, tapering to pointed tip (Figs. 40C, 41 D–E).

Last few cinctured segments narrowing to pygidium bearing ventral, disc-like lobe (Fig. 40B).

Methyl Green stain. Body stains more or less uniformly throughout; with a band of stain around the subapical part of the prostomium, tip of prostomium not staining at all; some stain concentrated in intersegmental grooves of mid-body segments.

Etymology: The species name biannulata is from the Latin, bis for two and annulatus for ringed, in reference to the two distinctly separate pre-setal rings consisting of the peristomium and an achaetous segment.

Remarks. Chaetozone biannulata n. sp. and C. australosetosa n. sp. form a species pair, with the first more common in deep-water slope depths and the second more common in shelf depths. Both species are unique among in the manner in which the peristomium is divided into two parts, the second of which is interpreted as an achaetous segment that merges seamlessly with the anterior border of setiger 1. The main differences between the two species are that C. biannulata n. sp. has a long, narrow triangular-shaped prostomium/peristomium whereas in C. australosetosa n. sp. this is short and conical. These differences result in the pre-setigerous region of C. australosetosa n. sp. being shorter and somewhat bulbous compared to the elongate triangular shape of C. biannulata n. sp.

Similarities and differences between C. australosetosa n. sp. and C. biannulata n. sp. with C. reticulata n. sp., another Antarctic species, and C. hystricosa from North America are discussed with C. australosetosa n. sp. (see above).

Habitat & biology. The majority of samples for which surficial sediment data was developed during ANDEEP I and II was predominately silt-clay with lesser amounts of sand or pebbles. The color of the mud was generally dark greenish-grey or brown (Howe et al. 2004, 2007). There was considerable evidence of bioturbation in the sediment profile images (Diaz 2004). The Powell Basin station sampled during ANDEEP III had surficial sediment that was fine-to-medium silt, poorly sorted with sand (3%), silt (66%), and clay (31%) (Howe et al. 2007).

Eggs measuring 60–100 µm observed in several ovigerous females from the Weddell Sea.

Distribution: Drake Passage and Scotia Sea, 421–3957 m; Weddell Sea to South Sandwich Trench, 743–6337 m; off South Shetland Islands, 400–606 m; South Pacific Ocean, E of New Zealand, 2100 m.