Trichobranchus glacialis Malmgren, 1866 by monotypy.

Figures 19–20

Trichobranchus glacialis,— Malmgren, 1866: 395–396, pl. 24 fig. 65.—McIntosh, 1922: 205–209, pl. 115 fig. 5, pl. 127 fig. 4.— Fauvel, 1927: 288–289, fig. 100a–h,— Holthe, 1986 b: 164–165, fig. 77, map 76.— Hutchings & Peart, 2000: table 4.

Material examined: SMA _ Tricho _02, two complete specimens, Northeast Atlantic Ocean, Brittany, Trévignon, MTR1, 47°47’30”N, 3°52’57”W, 11 m depth, February 2015 ; MNHN-IA-PNT 95, one specimen, anterior part, Northeast Atlantic Ocean, Brittany, Bay of Brest, ZC, 48°18’55”N, 4°21’54”W, 1.3 m depth, June 2016 ; MNHN- IA-PNT 96, one specimen, anterior part, Northeast Atlantic Ocean, Brittany, Bay of Brest, BK, 48°21’28”N, 4°26’38”W, 7 m depth, May 2018 ; MNHN-IA-PNT 97, one complete specimen, Northeast Atlantic Ocean, Brittany, Trévignon, MTR1, 47°47’30” N, 3°52’57” W, 11 m depth, February 2015 ; MNHN-IA-PNT 98, two specimens, Northeast Atlantic Ocean, Brittany, Bay of Brest, ZG, 48°17’19”N, 4°24’04”W, 2 m depth, June 2016 , mounted for SEM; SMA _ Tricho _05, one specimen, anterior part, Northeast Atlantic Ocean, Brittany, Bay of Brest, HA4, 48°19’18”N, 4°24’11”W, 2 m depth, June 2016 , mounted for SEM; SMA _ Tricho _14, two specimens, Northeast Atlantic Ocean, Brittany, Bay of Brest, BK, 48°21’28”N, 4°26’38”W, 7 m depth, May 2018 , mounted for SEM; MNHN-IA-PNT 99, complete (posterior part used for molecular analysis), Northeast Atlantic Ocean, Brittany, Bay of Brest, ZC, 48°18’55”N, 4°21’53”W, 5 m depth, May 2018 ; SMA _ Tricho _08, complete (posterior part used for molecular analysis), Northeast Atlantic Ocean, Brittany, Bay of Brest, ZC, 48°18’55”N, 4°21’53”W, 5 m depth, May 2018 .

Comparative material examined: BMNH 1923.3.22.47 (National History Museum, London). NMW. Z.2012.045.0072 and NMW.Z.2000.011.0102 (National Museum Wales, Cardiff). All specimens sampled in Norway.

Description. Medium size species, with length between 9.8 and 13.9 mm and width between 1.2 and 1.7 mm, thorax cylindrical, abdomen tapering (Fig. 19A).

Prostomium well developed, distal part extending transversely across base of upper lip, trilobed, with buccal tentacles originating laterally and mid-dorsally; long buccal tentacles of 2 types, thin and cylindrical, and thick and grooved (Figs 19C & 20 A–B). Two groups of black or brown eyespots, forming two dorsolateral areas, situated dorsally on prostomium. Peristomium with one pair of large ventrolateral flaring lobes (Figs 19A, D & 20A), with ciliary ridges, midventrally fused to lower lip; lower lip short, upper lip hidden by buccal tentacles. SG 1 dorsally inconspicuous, ventrally forming semicircular eversible process (Fig. 19C). SG 2–4 with ventral crests anteriorly raised, larger than following ones (Fig. 19C); following segments with short ventral crests. Dorsum smooth. Ventral groove absent. Three pairs of branchiae, on posterior parts of SG 2–4, each pair with single long and thick filament (extending to TC 3) (Figs 19B, D & 20 A–B); filaments wrinkled, with rounded tips (Figs 19B & 20B); pairs of branchiae progressively inserted mid dorsally (third pair with each filament joined) (Fig. 20B); filaments highly fragile and easily lost.

Notopodia starting from SG 6, extending for 15 segments, trapezoidal shaped, laterally aligned; first two pairs shorter than subsequent ones; narrowly-winged long bilimbate notochaetae, narrowly bilimbate. Neuropodia starting from SG 6, first thoracic neuropodia with few uncini, following ones with about 15 uncini per torus arranged in one irregular row; uncini with strong, distally blunt main fang and many rows of secondary teeth, presence of a sheath below main fang (Fig. 20C). About 45 abdominal neuropodia as erect pinnules paddle-shaped with distal margin provided with about 35 uncini; each with 2 rows of pointed secondary teeth above and laterally to main fang, surmounted by an upper crest of minute teeth (hardly visible) (Fig. 20D).

Nephridial papillae not seen. Pygidium bulbous and slightly crenulated (Fig. 19A).

Remarks. As pointed out by Garraffoni et al. (2005), the holotype of T. glacialis is not stored in any Swedish museum and is probably lost. In the absence of type material, we have compared our specimens with specimens from Norway: BMNH 1923.3.22.47, NMW.Z.2012.045.0072 and NMW.Z.2000.011.0102. The characteristics of French specimens correspond to those of Norwegian specimens but also to distinguishing characters summarized in Hutchings & Peart (2000, Table 4). Indeed, French specimens show three pairs of branchiae with 3 rd inserted middorsally, presence of eyespots, peristomium with a pair of large rounded thin and flexible lobes, presence of lateral lobes on segments 2 and 3, narrow double winged notochaetae, about 45 abdominal chaetigers, short abdominal neuropodia. To our knowledge, this study provides for the first time SEM plates for this species. SEM permitted to confirm the presence of a tuft of bristles along the lower surface of the main fang of thoracic uncini, as shown for Trichobranchus bunnabus Hutchings & Peart, 2000 . SEM also permitted us to distinguish an upper crest of minute teeth above the two rows of pointed secondary teeth of abdominal uncini.

Habitat. On mud, sand and mixed bottoms, uppermost sublittoral to depths exceeding 2500 m (Holthe 1986), maerl (rhodolith) beds, from 2 to 15 m depth (this study).

Distribution. Reported widely from Northern Europe; Mediterranean, Adriatic and Aegean Seas; Western North Atlantic, North Pacific, South, West and East Africa; South America, Arctic and Antarctica (Hutchings & Peart, 2000; Gil, 2011); Northern part of the Bay of Biscay (Bay of Brest, Trévignon, Belle-Ile) (this study). How- ever, molecular studies should be carried out to confirm this wide distribution and depth range.