Terebellides canopus Schüller & Hutchings, 2013, sp.n.

Terebellides canopus sp.n.

Figs 3, 4, 5

Holotype: ANDEEP III, St. 74-6, EBS (ZMH-26017)

Paratypes: ANDEEP III, St. 121-10, GKG (ZMH-26011); ANDEEP III, St. 121-10, GKG [drawing] (ZMH- 26012); ANDEEP III, St. 150-3, GKG [drawing, MG photo] (AM W39666); ANDEEP III, St. 150-3, GKG [drawing, MG photo, SEM, stub MI583] (AM W38717); ANDEEP III, St. 74-6, EBS (3 specimens, ZMH-26018, ZMH-26019, ZMH-26020); ANDEEP III, St. 150-6, EBS [SEM, stub MI490 & MI491] (AM W38718); ANDEEP III, St. 150-6, EBS (2 specimens, AM W39667, AM W39668); ANDEEP II, St. 46-7, EBS (ZMH-26031).

Description: (Based on both holotype and paratypes).

Holotype: 12 mm in length, 2 mm in width, posteriorly incomplete with 8 abdominal chaetigers. Paratypes range in length from 4–6 mm in length and 1 to 1.5 mm in width, all posteriorly incomplete, some with a few abdominal chaetigers, majority with only thoracic chaetigers.

Head region: Tentacular membrane expanded and folded. Lower lip rectangular, expanded and folded upwards with a smooth rim. Tentacles either only short simple ones present on outer margins of tentacular membrane (Fig. 3 A, B), or numerous long tentacles with expanded tips (Fig. 4 A, D).

Branchiae: Branchial lobes fused to about 50%, lamellae broad, but numerous and compact, without distinct filamentous tips (Figs 3 C, D, 4A, B). Posterior branchial lobes shorter (about 80% of anterior ones). Fifth branchial lobe absent. No evidence of ciliary fields between lamellae (Fig. 4 C). Annulation of branchial stem present, stem rather long and flattened (Fig. 3 C). Possibly juvenile branchial development with drop-shaped branchiae arranged at 120° angle to each other on one specimen (Figs 3 D, 5F).

Anterior chaetigers: Notopodia from segments 3–20, 18 pairs. First notopodia reduced in size compared to subsequent notopodia with chaetae more or less originating from body wall. Notochaetae, capillaries varying in length within fascicle (Fig. 4 D).

Neuropodia present from segment 8, those of TC-6 (chaetiger 6) geniculate hooks, about 7–9 per side, strongly bent with long extended fine tips (Fig. 4 E). Subsequent neuropodia with long shafted denticulate hooks with main fang and several rows of teeth above, not vertically aligned, so providing a dental formulae not possible (Fig. 4 G, H). Uncini arranged in single rows although may be irregular (Fig. 4 F) so as to appear as arranged in double rows. Abdominal uncini with numerous rows of elongate teeth extending to tip of uncinus covering the main fang (Fig. 4 H).

Lateral lappets: Present from TC-1–7, with TC-1=2=3=4>5<6>7 (Figs 3 A, B, 4D).

Ventral pads: Ventrum of thoracic segments strongly glandular with anterior margins of segments elevated, especially marked on chaetigers 1–4.

Nephridial papillae: Present on segments 3, 5, 6, 7, small globular slightly elongate (Fig. 5 E).

MG staining pattern 8 (Figs 2, 5): Solid to about TC-11 or -12, few subsequent segments with distinct stripes. No distinct white bands or pronounced anterior margins present, noto- and neuropodia stain.

Pygidium: Unknown.

Remarks: Terebellides canopus sp.n., is characterised by having a lower lip with smooth margin, branchial lobes at least partially fused along their length with lamellae densely packed, a single row of thoracic geniculate hooks and subsequent uncini arranged in single and sometimes in double rows. This new species resembles T. toliman sp.n., (this paper) as it also lacks the 5th branchial lobe, and branchiae are equipped with numerous branchial lamellae, densely packed, all lobes lacking filamentous tips, but can be easily separated by the shape of the nuchal hooks and by the development of lateral lappets. They are present to the 6th thoracic chaetiger in T. toliman sp.n., (this paper) and the 7th in T. canopus sp.n. The geniculate hooks are strongly bent in T. canopus sp.n., and weakly bent in T. toliman sp.n. Other species with partially fused branchial lobes with numerous lamellae include Terebellides californica Williams, 1984, Terebellides horikoshii Imajima & Williams, 1985, and Terebellides japonica Moore, 1903, but these all have lateral lappets only until the 5th thoracic chaetiger. For further details see the key.

Habitat: Known only from the eastern and western Weddell Sea continental slope to upper abyss and the Drake Passage in 1047–2621 m.

Etymology: The specific name canopus is the brightest star in the constellation Carina.