Terebellides gentili, Lavesque & Hutchings & Daffe & Nygren & Londoño-Mesa, 2019

Lavesque, Nicolas, Hutchings, Pat, Daffe, Gullemine, Nygren, Arne & Londoño-Mesa, Mario H., 2019, A revision of the French Trichobranchidae (Polychaeta), with descriptions of nine new species, Zootaxa 4664 (2), pp. 151-190 : 165-168

Terebellides gentili n. sp.

Figures 9–10 , Table 2

Type material: Holotype: MNHN-IA-TYPE 1870, complete, gravid, English Channel, Brittany, Morlaix Bay, Pierre Noire , 48°42’30”N, 3°51’58”W, 17 m depth, March 2015 . Paratypes: MNHN-IA-TYPE 1871, one specimen, incomplete, gravid, English Channel, Brittany, Morlaix Bay, Pierre Noire , 48°42’30”N, 3°51’58”W, 17 m depth, March 2015 ; MNHN-IA-TYPE 1872, one specimen, complete, English Channel, Brittany, Morlaix Bay , Château du Taureau, 48°40’26”N, 3°53’02”W, 12 m depth, August 2015 ; MNHN-IA-TYPE 1873, one specimen, complete, gravid, English Channel, Brittany, Morlaix Bay , Pierre Noire, 48°42’30”N, 3°51’58”W, 17 m depth, March 2015 , mounted for SEM; AM W.51395, one specimen, incomplete, English Channel, Brittany, Morlaix Bay, Pierre Noire , 48°42’30”N, 3°51’58”W, 17 m depth, March 2018 .

Additional material examined: AM W.51396, one specimen, complete, Northeast Atlantic Ocean, Brittany, Bay of Brest , MF1, 48°18’05” N, 4°19’26”W, 2 m depth, January 2016 ; SMA _ROS_08, one specimen, complete, gravid, English Channel, Brittany, Morlaix Bay, Pierre Noire , 48°42’30”N, 3°51’58”W, 17 m depth, October 2014 . SMA _BR_08, complete, gravid, Northeast Atlantic Ocean, Brittany, Bay of Brest, Camaret , 48°17’48”N, 4°34’59”W, 15 m depth, March 2015 ; SMA _OUI_02, one specimen, complete, English Channel, Bay of Seine , 49°26’05”N, 0°11’00”W, 30 m depth, April 2018 .

Description. Large species, with holotype 30.4 mm long (15.1–31.9 mm) and 2.8 mm (1.5–2.8 mm). Body tapering posteriorly with segments becoming increasingly shorter and more compacted towards pygidium.

Prostomium compact; eyespots absent; large upper lip surrounding mouth with many buccal tentacles ( Figs 9 C–D & 10A). Buccal tentacles of 2 types, uniformly cylindrical and with expanded tips, spatulate ( Fig. 10A ). Lower lip forming an expanded structure below upper lip ( Figs 9A –D & 10A ). SG 1 and 2 short, only visible ventrally; following segments with lobes as ventral collars ( Figs 9 A–B, D & 10A). Lateral lappets on SG 3–6, ( TC 1–4), continuing ventrally in TC 1–5, largest on TC 1 and declining in size posteriorly. No conspicuous dorsal rounded projection on anterior chaetigers. Elongated glandular lateral region on TC 3, with ventral portion pointed anteriorly ( Fig. 9B, D ).

Branchiae arising as a single structure from TC 1, reaching TC 6 ( TC 5), consisting of a single elongate and an- nulated stalk placed mid-dorsally ( Figs 9 A–D & 10A), two pairs of lobes, fused for about 1/2 of length, lower pair thinner ( Fig. 9C ). Upper lobes with 50 to 70 tightly packed lamellae ( Figs 9 A–D & 10A). Both sides of branchial lamellae provided with several parallel rows of cilia and tufts of cilia on outer edge ( Fig. 10B ). Most of individual lamellae of each branchia with widely spaced elongated small projecting papillae, visible under stereomicroscope ( Fig. 10 A–B). Distal region of both upper and lower lobes with long terminal pointed projections ( Figs 9 B–C & 10A). Anterior branchial projection (5 th lobe) present ( Figs 9 A–C & 10A).

Eighteen pairs of thoracic notopodia ( SG 3–20). First notopodium slightly smaller than subsequent notopodia; notochaetae from TC 1 slightly smaller in length than following notochaetae, and transversally aligned ( Figs 9B, D & 10A ). All notochaetae simple capillaries, arranged in two rows. Neuropodia present as sessile pinnules from TC 6 ( SG 8) to pygidium; uncini arranged in single rows from TC 7. First thoracic neuropodium ( TC 6) provided with four to six sharply bent acute tipped, geniculate chaetae. All subsequent thoracic neuropodia with about 11–15 uncini per torus arranged in one irregular row. Uncini as shafted denticulate hooks provided with long, thin and pointed main fang, straight terminally. Three or four teeth above the main fang, surmounted by a row of five to six short denticles and an upper crest of several smaller denticles ( Fig. 10C ). About 30 abdominal neuropodia as erect pinnules paddleshaped with entire margin provided with about 30 uncini; each with four pointed teeth above main fang, surmounted by a row of three short pointed teeth and an upper crest of minute teeth ( Fig. 10D ).

Two pairs of flattened nephridial papillae, located dorso-posteriorly to each notopodium from TC 4 to TC 5. Pygidium blunt, as a funnel-like depression.

Methyl green staining pattern. Stained with distinct stripes on each notopodial segments, from CH 1 to CH 12, bands becoming narrower and more widely spaced (stripes of first four chaetigers more or less visible depending on contraction of chaetigers); elongated whitish glandular region on TC 3 with central line more intensive stained ( Fig. 9D ).

Etymology. The species is named after Dr. Franck Gentil, for his many contributions to benthic ecology of English Channel. This species name was chosen in agreement with Céline Houbin and Caroline Broudin, from Roscoff laboratory, who were mentored by FG for many years.

Habitat. Coastal fine sands and maerl (rhodolith) beds, from 2 to 35 m depth.

Type locality. Morlaix Bay , English Channel, France .

Distribution. Bay of Biscay (Bay of Brest), English Channel (Morlaix and Bay of Seine), France, NE Atlantic ( Fig. 1 ).

Remarks. Except T. stroemii from Adriatic Sea ( Parapar et al. 2013) (see T. lilasae n. sp. remarks), T erebellides gentili n. sp. differs from other European previously known species by the presence of papillar projections pointing over the edge of the branchial lamellae. This character is similar to that present in T. gentili n. sp. and T. bonifi n. sp., T. europaea n. sp., T. lilasae n. sp. and Terebellides resomari n. sp. Among these species, only T. europaea n. sp., shares the presence of an undulating glandular region on TC 3. However, T. gentili n. sp. differs from T. europaea n. sp. by the presence of papillar projections on most of the branchial lamellae (instead of anterior lamellae only for T. europaea n. sp.), by the shape of papillar projections (small, elongated and widely spaced for T. gentili n. sp., rounded for T. europaea n. sp.), by the degree of fusion of lobes (1/2 of length for T. gentili n. sp., not fused for T. europaea n. sp.), the presence terminal projections of lower lobes (short and pointed for T. gentili n. sp., short filaments for T. europaea n. sp.) and by the MG pattern (striped from TC 1 to TC 12 for T. gentili n. sp., compact from TC 1 to TC 9 for T. europaea n. sp.) ( Table 2 ).

Figures

FIGURE 1. Schematic distribution of the different Trichobranchidae species along the French coasts. Text in italic represents type locality of new species. Abbreviation: WGMP, West Gironde Mud Patch.

FIGURE 9. Terebellides gentili n. sp. holotype MNHN-IA-TYPE 1870 (A–C) and paratype MNHN-IA-TYPE 1871 (D) A. Entire worm, lateral view; B. Anterior part, lateral view; C. Anterior part, dorsal view; D. Anterior part, lateral view, methyl green staining. Abbreviation: glr, glandular lateral region. Scales: A=4 mm, B–D=1 mm.

FIGURE 10. Terebellides gentili n. sp. SEM paratype MNHN-IA-TYPE 1873 A. Anterior part, lateral view; B. Papillar projections on edge of branchial lamellae, lateral view; C. Uncini, thoracic chaetiger; D. Uncini, abdominal chaetiger. Scales: A=400 µm, B=90 µm, C=25 µm, D=15 µm.