Terebellides kirkegaardi Parapar & Martin & Moreira 2020, sp. nov.

Terebellides kirkegaardi sp. nov.

Figures 11B, 21A, 22–24, 37; Tables 1, 2

urn:lsid:zoobank.org:act: 82974B42- 2924-48 A8-BD1A-254FED0F881B

Material examined. Type material. Holotype (NHMD-231439); paratypes: 37 specimens (NHMD-636923 to NHMD-636925), all from the same original vial as the holotype (Table 1).

Diagnosis. Body of medium/large size (15–30 mm in length). Branchiae with a long and thick stalk; anterior lobe large; posterior ventral lobes about as long as dorsal ones, with short terminal filaments, emerging directly from branchial stem. TC1 notopodia and notochaetae shorter than following thoracic ones. Thoracic neurochaetae with rostrum / capitium length about 2/1, and capitium with a first row of 2–5 medium-sized teeth followed by progressively smaller ones.

Description based on holotype

Measurements and general body features. Complete specimen, 28.0 mm long and 2.5 mm wide (Fig. 21A, 22 A−B); body tapering posteriorly with segments increasingly shorter and crowded towards pygidium. Prostomium compact; large tentacular membrane surrounding mouth, with typical buccal tentacles with expanded tips (Fig. 22 A−Β). SG1 as an expanded structure below tentacular membrane (Fig. 22A, 24A). Lateral lappets and ovalshaped glandular region in TC3 not present.

Branchiae. Branchiae arising as single structure from SG3, consisting of a single very long (about same length as dorsal posterior lobes) stalked mid-dorsal branch (Fig. 21A, 22 A−D, 24A), with one pair of dorsal (upper) un- fused lobes reaching TC4 or TC6 (if branchial stalk bent backwards); a pair of ventral (lower) lobes about as long as dorsal ones but thinner, not fused together and arising directly from stalk (Fig. 21A, 22 A−D, 23A, 24A). Ante- rior projection of dorsal lobes (lobe 5) very well developed, about half length of posterior dorsal lobes (Fig. 21A, 22 A−D, 23A, 24A). Pointed projection of posterior region of both upper and lower lobes much longer in ventral ones, becoming a terminal filament (Fig. 23A). Both sides of branchial lamellae ciliated, arrangement in rows and/ or tufts or papillae not seen.

Thorax. Eighteen pairs of notopodia (SG3−20); that of TC1 shorter than subsequent ones (Fig. 24 A−B), with notochaetae as simple capillaries, shorter in number and length than following ones. Neuropodia as sessile pinnules, from TC6 (SG8) to pygidium, with uncini in single rows starting from TC7 (SG9) throughout. First neuropodia (TC6) with 4–5 sharply bent, acute-tipped, geniculate chaetae (Fig. 23B, 24 C−D) having minute teeth forming a very low marked capitium (Fig. 24D). From TC7, neuropodia with 11–17 uncini per torus in one row (Fig. 24E) with long shafted denticulate hooks, rostrum about two times longer than capitium, with 2−5 big teeth above main fang, and surmounted by a crest of smaller denticles (Fig. 24 F−G).

Abdomen. About 40% of body length, with 31 pairs of neuropodia as erect pinnules with about 20–25 uncini per torus having four teeth above main fang surmounted by a crest of several teeth of same and/or smaller length (Fig. 23D).

Other features. Papilla on first thoracic notopodia not seen; button-hole-like pairs of dorsal nephridial openings on, at least, each SG7 (TC5) notopodium (Fig. 23 B−C); second pair not seen. Pygidium blunt, as funnel-like depression.

Methyl green staining pattern. Anterior CH 1 to CH 3 solid; CH 4 to CH 9 striped; fading from CH 10 to CH 12; J-shaped glandular region marked lateral to CH 3; pattern 5 of Schüller & Hutchings (2010) (Fig. 37).

Variations. Terebellides kirkegaardi sp. nov. is a medium-sized species (15−30 mm long). Eggs were visible in body cavity of females across all length range. Most specimens are in good conditions, with bodies and branchiae complete.

Type locality. Cameroon; 8–9 m depth (Table 1).

Distribution and bathymetry. Victoria (aka Limbé, Cameroon); 8−9 m depth (Fig. 11B; Table 1).

Etymology. This species is named in honour of Danish researcher Jørgen Bagger Kirkegaard (1920−2006), who participated in the Galathea and Atlantide Deep Sea Expeditions. His 1958 publication on West African sedentary polychaetes included most of the specimens studied in the present work.

Remarks. Terebellides kirkegaardi sp. nov. is mostly characterised by its long branchial stalk and well-developed anterior triangular lobe, coupled with a TC1 notopodia shorter than following, and very low marked capitium teeth in TC6 thoracic uncini (only detected with SEM). The branchial appearance is similar across most specimens studied (cfr. Fig. 21A, 22 A–D, 24A)—but see Fig. 22 E–F, 23A—giving rise to a characteristic body profile that differs from any other known species of the genus.

Terebellides kirkegaardi sp. nov. most closely resembles Terebellides canopus Schüller & Hutchings, 2013, Terebellides mira Schüller & Hutchings, 2013 (both from deep waters off South Western Atlantic Ocean), and Terebellides sepultura Garraffoni & Lana, 2003 (from Brazilian coasts). However, they lack the anterior projection of branchial lobes and posterior lobes are free from each other. Terebellides mira also bears a branchial stem that is much longer than the proper branchial lobes. Two specimens from Myanmar, identified as Terebellides cf. woolawa Hutchings & Peart, 2000 by Parapar et al. (2016a), also show long branchial stems, but differ from T. kirkegaardi sp. nov. in having an even more developed, non-triangular anterior lobe, as well as smaller postero-ventral lobes. Furthermore, T. woolawa as described by Hutchings & Peart (2000) bears a similar anterior lobe, but the branchial stem is much shorter.