Tharyx coloris Blake 2018, new species

Tharyx coloris new species

Figures 54–55

Chaetozone sp. 1: Hilbig 2001: 540 (in part); Hilbig et al. 2006: 715, 717–719, 724 (in part).

Material examined. East Antarctic Peninsula, Prince Gustav Channel, RVIB Nathaniel B. Palmer Cr. 2000-3, coll. J.A. Blake, SM Grab, Sta. 01, 14 May 2000, 64°17.625ʹS, 058°34.678ʹW, 768 m, holotype (LACM-AHF Poly 10225) and 50 paratypes (LACM-AHF Poly 10226); Sta. 27, 23 May 2000, 64°22.934ʹS, 58°36.976ʹW, 684 m, 11 paratypes (LACM-AHF Poly 10227); Sta. 28, 23 May 2000, 64°22.018ʹS, 058°30.942ʹW, 794 m, 37 paratypes (LACM-AHF Poly 10228); Sta. 29, 24 May 2000, 64°21.361ʹS, 058°26.637ʹW, 690 m, 29 paratypes (USNM 1490746); Sta. 30, 24 May 2000, 64°16.875ʹS, 058°26.985ʹW, 843 m, 8 paratypes (USNM 1490747); Sta. 33, 24 May 2000, 64°11.959ʹS, 058°41.857ʹW, 587 m, 11 paratypes (USNM 1490748); Sta. 34, 24 May 2000, 64°10.995ʹS, 058°34.140ʹW, 865 m, 15 paratypes (MCZ 149854); Sta. 35, 25 May 2000, 64°10.471ʹS, 058°28.505ʹW, 651 m, 14 paratypes (MCZ 149855.— East Antarctic Peninsula, Former Larsen Ice Shelf A area, Greenpeace Trough, RVIB Nathaniel B. Palmer Cr. 2000-3, coll. J.A. Blake, SM grab, Sta. 7B, 18 May 2000, 64°43.523ʹS, 060°04.771ʹW, 839 m (1, JAB); border with Larsen B , RVIB Nathaniel B. Palmer Cr. 2000-3, coll. J.A. Blake, SM grab, Sta. 12, 19 May 2000, 64°55.101ʹS, 060°24.459ʹW, 317 m (2, JAB); Sta. 13, 19 May 2000, 64°53.517ʹS, 060°28.836ʹW, 323 m (3, JAB); Sta. 14, 19 May 2000, 64°51.818ʹS, 060°33.438ʹW, 419 m (3, JAB); Greenpeace Trough, Sta. 18, 20 May 2000, 64°39.381ʹS, 059°59.498ʹW, 665 m (1, JAB).— Weddell Sea, east of former Larsen Ice Shelf A area, RVIB Nathaniel B. Palmer Cr. 2000-3, coll. J.A. Blake, SM grab, Sta. 26, 23 May 2000, 64°39.564ʹS, 059°13.226ʹW, 564 m (26, MCZ 149856); Weddell Sea, SW of Vestkapp, EASIZ II, R / V Polarstern, ANT-XV/3, coll. B. Hilbig, Sta. MG 48-093, 4 Feb 1998, 73°28.3ʹS, 22°54.5ʹW, 1988 m, 994 m, (4, SMF 24937); Weddell Sea, off Coats Land, USCG Glacier, Sta. 69-8, 02 Mar 1969, 77°36.2ʹS, 42°30ʹW, 585 m (1, USNM 1490749).

Description. A moderately sized species, holotype complete, 9.3 mm long, 0.65 mm wide across gravid middle body segments, with 85 setigerous segments. Largest paratypes similar, 9–9.5 mm long with 75–90 segments. Body elongate, generally widest in gravid middle body segments, narrowing in far posterior segments. Anterior segments narrow, about ten times wider than long (Fig. 54A); posterior segments narrower, about three times wider than long (Fig. 54C); moniliform or oblong segments absent. Dorsal groove or ridge absent, dorsum broad, relatively smooth anteriorly; with shallow ventral groove present from anterior segments to near posterior end (Fig. 55C); this groove typically with a mid-ventral bulge in each segment where two sides join resulting in low ridge. Color in alcohol overall light tan, but with distinctive brownish-red pigment scattered over peristomium, anterior parapodia, and branchial stubs (Fig. 55B); ventrally pigment on each segment follows contours across mid-ventral groove and central ridge (Fig. 55C). This pigment very dark and intense on some specimens, faded in others; highly diagnostic for this species.

Prostomium broad, triangular, narrowing to rounded tip (Figs. 54 A–B, 55B–D); eyespots absent; nuchal organs shallow grooves on posterior lateral margin of prostomium (Figs. 54B, 55D). Peristomium broad, wider than long, with three annular rings, best seen dorsally (Fig. 54 A–B); middle ring largest, dorsally expanded, extending anteriorly over first ring and posteriorly over third ring, forming rounded dorsal crest (Fig. 54 A–B). Third ring narrow, similar in shape to setiger 1 and may be an achaetous segment; dorsal tentacles and first pair of branchiae arising on third ring with branchiae located lateral and slightly posterior to tentacles (Fig. 54 A–B). Second pair of branchiae on setiger 1 dorsal to notosetae (Fig. 54 A–B); branchiae of following segments in similar location; branchiae observed on segments in middle body segments but not in posterior segments.

Parapodia reduced to simple setal tori; postsetal lamellae absent. Setal fascicles of noto- and neuropodia close together throughout body. Notosetae long capillaries including long natatory-like setae throughout most of body, absent in smaller specimens; notosetae of anterior segments 6–10 per fascicle, reduced to 3–5 posteriorly; notoacicular spines entirely absent. Neuroacicular spines relatively simple, first present from about setiger 60 or later; individual spines geniculate to sickle-shaped, tapering to narrow sub-bidentate or knobbed tip (Fig. 54 D–F), detail of tips difficult to observe in some views, with some appearing to have angled tips (Fig. 55E); some posterior fascicles with up to 5–6 spines per neuropodium with some having geniculate shaft with capillary tips (Fig. 54G) and transitioning to blunt-tipped spines (Fig. 54 D–F); spines curved toward notopodia.

Last few segments narrowing to short pygidium bearing single rounded lobe ventral to anal opening (Fig. 54C).

Methyl Green stain. No distinct staining pattern anywhere along body; stain retained only in intersegmental furrows.

Etymology. Coloris is Latin for hue or tint, referring to the reddish colored pigment prominent on the anterior body segments of this species.

Remarks. Tharyx coloris n. sp. is superficially similar to Chaetozone homosetosa with which it may co-occur. A careful comparison of pigment, Methyl Green staining reactions, and the morphology of both soft and hard body parts confirmed that two different species were present. Tharyx coloris n. sp. differs from other species of Tharyx globally by having distinctive reddish-brown pigment over much of the body and from Antarctic species by the entire absence of notoacicular spines.

Habitat & biology. Specimens from the East Antarctic Peninsula were collected in May 2000. Mature females were present with numerous eggs in individual parapodia from about setiger 15 and continuing to about 20 setigers from the pygidium. The largest eggs ranged from 170–180 µm in the longest dimension.

Tharyx coloris n. sp. is one of several bitentaculate cirratulids common in the vicinity of the Prince Gustav Channel and the former Larsen Ice Shelf A collected in May 2000. The surficial sediments at these locations consisted of 20–40% sand in the upper 0–5 cm (Gilbert & Domack 2003).

Distribution. East Antarctic Peninsula, 317–794 m; Weddell Sea, 564–1988 m.