Terebellides diva, 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 : 23-25

Terebellides diva sp. n.

Figs 16–18

Etymology: The name is given in reference to the expedition Diva 3 during which the species was collected.

Diagnosis: The species can be recognized by its slender branchiae with a long stem and a few loose lamellae. In addition, the lower lip and especially the tentacular membrane are greatly expanded resulting in a “chunky” head region.

Holotype: Diva 3; st 604; EBS; 03°57.67'S, 28°05.36'W, 5179.8 m (start trawl) to 03°57.68'S, 28°05.28'W, ~ 5220 m (gear off ground); 05.08.2009; Brazil Basin (ZMH-25955)

Paratypes: 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 (1 specimen, ZMH-25956 [SEM])

Description: Holotype and paratype 1.5 mm long, 0.8 mm wide, incomplete.

Prostomium with lower lip strongly expanded but without apparent folds. Tentacular membrane very thick, fleshy and expanded, with buccal tentacles attached laterally and dorsally on anterior and posterior margins ( Figs 16a, b, 18a–c). Tentacles of varying length, mostly very long, simple or with expanded tips. Upper lip hardly visible, almost completely covered by lower lip from ventrum. First segment hardly visible in lateral view, second segment visible ventrally and expanded, only laterally covered by third segment ( Fig. 16b). Third segment of holotype with similar midventral expansion as segment 2 ( Fig. 16a). Lateral lappets on segments 3–7 (TC-1 - 5), only that of TC-1 and TC-2 well developed, size usually TC-1 = TC-2> TC-3> TC-4 = TC-5 ( Fig. 16a, b).

Ventral glandular bands and glandular areas around parapodia absent. Nephridial papillae visible dorsally to notopodia of segments 3 and 5, further nephridial papillae not observed but possibly present.

Branchiae consisting of a single stem dorsally between TC-1 and TC-2, stem prolonged in paratype, articulation not apparent ( Figs 16a, b, 17a). Four branchial lobes completely free from each other, bearing few, loose lamellae. Posterior lobes thinner than anterior lobes, of similar length, but proximally slightly shorter. Filamentous tips at the end of the branchial lobes present.

Notopodia all comparably well developed throughout thorax, that of TC-1 smaller than subsequent, covered by lateral lappet. Notochaetae all capillaries of similar length, arranged in 2 tiers, with almost smooth surfaces ( Fig. 17b).

First neuropodia from segment 8 (TC-6), as sessile pinnules in thorax. First neuropodium (TC-6) bearing about 3 acicular hooks, sharply bent with fine upwards bent tips. Acicular hooks seemingly without capitium on the outer side of the bend, up to bend almost completely embedded in body wall ( Fig. 17c). Subsequent thoracic neuropodia with series of few long-handled uncini, with stout main fang (MF) and numerous small teeth above MF ( Fig. 17d). Abdominal neuropodia and pygidium unknown.

MG staining ( Fig. 18a–c) corresponds with staining pattern 1 ( Schüller & Hutchings 2010), with all TCs almost solidly in anterior region and distinctly striped in median thorax until TC-11. Clearly apparent white bands missing. Notopodia unstained while neuropodia bear a green colouration under fresh staining.

Remarks: As T. concertina sp. n., this species also lacks the somewhat frayed surface of notochaetae caused by bent capillary thecae, and an apparent capitium of the acicular hooks in TC-6. Also the overall appearance of T. diva sp. n., is most similar to T. concertina sp.n., in that they bear a rather compact head region. However, judging from the length of the anterior thorax, T. diva sp. n. seems to represent a smaller species. In addition, the two species are clearly separated from each other by the extent of anterior segments which are ventrally and laterally broad in T. diva sp. n., and very narrow in T. concertina sp. n., and their lateral lappets ( T. diva sp. n.: TC-1 = TC-2> TC-3> TC-4 = TC-5; T. concertina sp. n.: TC-1 <TC-2 <TC-3>= TC-4> TC-5 <TC-6> TC-7).

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.