Terebellides bulbosa, Schüller & Hutchings, 2012

Schüller, M. & Hutchings, P. A., 2012, New species of Terebellides (Polychaeta: Trichobranchidae) indicate long-distance dispersal between western South Atlantic deep-sea basins, Zootaxa 3254, pp. 1-31 : 15-19

Terebellides bulbosa sp. n.

Figs 10–12

Etymology: The name refers to the characteristic expansion of the anterior segments of the species.

Diagnosis: The species can be distinguished by its first four chaetigers with their large lateral lappets, followed by a series of laterally expanded segments before the typical Terebellides -shaped posterior thorax begins, giving the species the appearance of consisting of three parts.

Holotype: Diva 3; st 605; EBS; 3°57.49'S, 28°4.67'W, 5188.5 m (start trawl) to 3°57.54'S, 28°4.51'W, 5184.8 m (gear off ground); 06.08.2009; Brazil Basin (ZMH-25950)

Paratypes: Diva 3; st 561; EBS; 26°34.78'S, 35°13.90'W, 4484.4 m (start trawl) to 26°34.96'S, 35°13.89'W, 4493.0 m (gear off ground); 23.07.2009; NW off Rio Grande Rise (1 specimen, ZMH 25949 [SEM])

Description: Length of holotype 1.6 mm with part of abdomen missing, width about 0.8 mm. 18 thoracic chaetigers (TCs), starting from segment 3, neuropodia bearing uncini first present in segment 8 (TC-6); 17 abdominal segments still present. Pygidium absent. Paratype 5 mm long and 0.3 mm wide for 21 abdominal uncinigers, complete.

Thorax appears to consist of three sectors: (1) first three to four chaetigers largely expanded laterally, (2) median chaetigers with lateral part below notopodia somewhat bulbous, inflated, segments clearly separated from each other, and (3) posterior chaetigers with no such expansions, parapodia further apart from each other, segmental borders not apparent ( Fig. 10).

Lower lip simple, rectangular, widely expanded ( Figs 11a, 12c, d). Tentacular membrane consisting of two transverse folds with short tentacles on its outer margin ( Fig. 10). First segment and second segment hardly visible, mostly covered by segment 3 (TC-1) ( Fig. 11b). Segments 3 to 5 (TC-1 - 3) with very large lateral lappets reaching from the dorsum to the ventrum. Lateral lappet on segment 6 (TC-4) also large, but not as wide and expanded dorsally. Lateral lappets on segments 5–6 (TC-3 - 5) present but distinctly smaller than previous ones ( Figs 10, 11a, 12a, d).

Ventral glandular bands and glandular areas around parapodia absent. Nephridial papillae present in TC-5, further nephridial papillae not apparent in observed specimens ( Fig. 10).

Branchiae consisting of a stout single stem dorsally between TC-1 and TC-2, branchial lobes lost ( Fig. 10).

Notopodia of TC-1 reduced in size, that of TC-2 still smaller than subsequent ones, all following comparably well developed throughout thorax. All chaetae simple capillaries, arranged in two tiers, proximal parts of capillaries strongly bent resulting in a frayed chaetal surface ( Fig. 11c).

First neuropodia from segment 8 (TC-6), as sessile pinnules in thorax. First neuropodium (TC-6) bearing strongly protruding sharply bent acicular hooks. Subsequent thoracic neuropodia bearing a series of few (about 5) long-handled uncini. Main fang of uncini stout, about as long as width of uncini and sharply bent. Head of uncini covered by numerous smaller teeth ( Fig. 11d). Abdominal neuropodia present as erect pinnules with few uncini (about 3–5) each. Abdominal uncini with a main fang, two rows of teeth arranged in semi-circles of 3 (inner row) and 6 (outer row) plus outer rows of numerous small teeth.

MG staining ( Fig. 12a–d) with TC-1 - 10 solidly stained, striped in TC-11, subsequent segments without staining. Distinct white bands on anterior ventrum of segments missing. Notopodia and dorsum between notopodia remain unstained, thoracic neuropodia stained in TC-6 - 11.

Remarks: The characteristic three-parted development of the species’ thorax is present in all specimens found to various extent and thus represents a true character that differentiates the species from all other species of Terebellides . Another characteristic of the species is the widely expanded lower lip that is reminiscent of a saucer when viewed ventrally and reaches as far as the branchial stem on the dorsum forming a collar between the head region and the first TC.

For comments as to how this species varies from other formerly described species in the western South Atlantic see the Discussion, but it should be noted that no other species of Terebellides have been described from such deep water in the South Atlantic to date.