Terebellides concertina, 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 : 19-23

Terebellides concertina sp. n.

Figs 13–15

Etymology: The name refers to the shape of the anterior thoracic chaetigers that are narrow but laterally expanded similar to a partially compressed accordion.

Diagnosis: The species can be recognized by the first and second segment that are conspicuous laterally, and the lateral lappets which are characterized by distinct lateral extensions rather than by anterior expansions resulting in narrow anterior chaetigers.

Holotype: Diva 3; st 534; EBS; 36°0.61'S, 49°1.54'W, 4607.8 m (start trawl) to 36°0.70'S, 49°1.73'W, 4576.1 m (gear off ground); 16.07.2009; Argentine Basin (ZMH-25952)

Paratypes: Diva 3; st 534; EBS; 36°0.61'S, 49°1.54'W, 4607.8 m (start trawl) to 36°0.70'S, 49°1.73'W, 4576.1 m (gear off ground); 16.07.2009; Argentine Basin (1 specimen, ZMH-25953 [SEM])

Diva 3; st 533; EBS; 36°0.20'S, 49°1.96'W, 4601.8 m (start trawl) to 36°0.27'S, 49°2.13'W, 4604.0 m (gear off ground); 15.07.2009; Argentine Basin (1 specimen, ZMH-25951)

Description: Holotype 20 mm long, 5 mm wide, incomplete, ovigerous. Size of observed specimens varies from 2 mm to about 7 mm, all incomplete. Maximum width up to 2.5 mm.

Prostomium with lower lip with folds in lateral regions and anteriorly expanded median region ( Fig. 13a, c). Tentacular membrane expanded ( Fig. 14a, b), surrounded by buccal tentacles of varying length, simple and with expanded tips ( Figs 13a, b, 15a–c). Upper lip hardly visible, mostly covered by lower lip from ventrum. First segment well visible laterally, second segment well visible in ventral and lateral view, barely covered by expanded third segment ( Fig. 13a, c). Third segment bearing two distinct longitudinal folds midventrally ( Figs 13c, 15a, b). Lateral lappets on segments 3–9 (TC-1 - 7), well developed, size usually TC-1 <TC-2 <TC-3>= TC-4> TC-5 <TC-6> TC-7 ( Figs. 13a, 14a, b).

Ventral glandular bands and glandular areas around parapodia absent. Nephridial papillae inserted dorsally to notopodia of segments 5, 6, 7 and 8 (TC-3 - 6) ( Fig. 13b).

Branchiae consisting of a stout single stem dorsally between TC-1 and TC-2 ( Fig. 13b). Four branchial lobes completely free from each other, bearing broad, oval-elongated lamellae that are tightly packed. Posterior lobes shorter (about 80%) and less in diameter than anterior lobes. Branchial stem annulated, filamentous tips at end of branchial lobes absent.

Notopodia all comparably well developed throughout thorax, that of TC-1 smaller than subsequent ones. Notochaetae all capillaries of 2 lengths arranged in 2 tiers ( Fig. 14c). Chaetal surface almost smooth, only weakly structured by upwards bent ends of chaetal thecae.

First neuropodia from segment 8 (TC-6), as sessile pinnules in thorax. First neuropodium (TC-6) bearing about 2–4 acicular hooks on a slightly elevated ridge. Hooks weakly bent with fine downwards bent tips, part of hooks below bend almost completely embedded in body wall ( Fig. 14d, e). No capitium apparent. Subsequent thoracic neuropodia with long-handled uncini ( Fig. 14f), arranged in single rows per torus, with a stout and distinctly prolonged main fang (MF) and numerous small teeth above MF.

Abdominal neuropodia and pygidium unknown.

MG staining ( Fig. 15a–c) corresponds with staining pattern 4 ( Schüller & Hutchings 2010), with all TCs almost solidly stained. Clearly apparent white bands missing. Noto- and neuropodia bearing green colouration with fresh staining.

Remarks: In comparison to all other Terebellides species found during the expedition Diva 3 this species represents a large species with a very broad and stout appearance. The anterior thorax is compact and less delicate than in the other species, and thus resembling shallow water species of Terebellides . Additional characters which they share with shallow water species of the genus are the lack of a capitium in the acicular hooks and the more or less smooth chaetal surface. Since the holotype is an ovigerous female it is, however, without doubt that the species is a real deep-sea species that also reproduces in the deep, and populations do not consist of recruits from shelf or slope environments.

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.