Terebellides gralli, 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 : 168-170

Terebellides gralli n. sp.

Figures 11–12 , Table 2

Type material. Holotype: MNHN-IA-TYPE 1874, complete, Northeast Atlantic Ocean, Brittany, Bay of Brest , ME2, 48°18’31”N, 4°21’56”W, 1 m depth, June 2016 . Paratypes: MNHN-IA-TYPE 1875, complete, Northeast Atlantic Ocean, Brittany, Bay of Brest , ZC, 48°18’55”N, 4°21’54”W, 1.3 m depth, January 2016 ; MNHN-IA-TYPE 1876, two complete specimens, Northeast Atlantic Ocean, Brittany, Bay of Brest , HA, 48°19’18”N, 4°24’11”W, 2 m depth, June 2016 , mounted for SEM; MNHN-IA-TYPE 1877, complete, Northeast Atlantic Ocean, Brittany, Bay of Brest , LC3, 48°18’39”N, 4°21’22”W, 1.4 m depth, January 2016 ; AM W.52079, complete, Northeast Atlantic Ocean, Brittany, Bay of Brest , VC, 48°18’59”N, 4°23’28”W, 2.2 m depth, October 2015 ; MNHN-IA-TYPE 1878, 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 .

Additional material: SMA _ROS_02, one specimen, incomplete, gravid, English Channel, Brittany, Morlaix Bay, Pierre Noire , 48°42’30”N, 3°51’58”W, 17 m depth, March 2018 .

Description. Small size species, with holotype 18.9 mm long (8.3–19.8 mm) and 1.2 mm (0.8–1.4 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 ( Fig. 11 A–D). Buccal tentacles of 2 types, uniformly cylindrical and with expanded tips, spatulate ( Figs 11 B–D & 12A– B). Lower lip forming an expanded structure below upper lip ( Fig. 11 A–C). S1 and S2 short, only visible ventrally; following segments with lobes as ventral collars ( Fig. 11 A–C). Lateral lappets on SG 3–6 ( TC 1–5), continuing ventrally in TC 1–5, largest on TC 1 and 2 and declining in size posteriorly. No conspicuous dorsal rounded projection on anterior chaetigers. Postero-lateral crescent moon-shaped glandular region on TC 3 ( Fig. 11 B–C).

Branchiae arising as a single structure from TC 1 and reaching TC 4 ( TC 6), consisting of a single elongate and annulated stalk situated mid-dorsally, made up of two pairs of lobes fused on less than1/2 of length, lower pair thinner ( Figs 11B, D & 12B ). Posterior region of upper lobes with long pointed projections and lower lobes with short terminal pointed projections ( Figs 11B, D & 12B ). Upper lobes provided with about 40 well packed to loosely fused lamellae, lamellae of different width and size ( Figs 11 A–D & 12A–B). Both sides of branchial lamellae provided with five to six well-marked parallel rows of cilia, no tufts of cilia on outer edge. Absence of papillar projections over the margins of the branchial lamellae ( Fig. 11 A–B). Anterior branchial projection (5 th lobe) present ( Fig. 11 A–C).

Eighteen pairs of thoracic notopodia ( SG 3–20; TC 1–18). Notopodia present from TC 1 well–developed; notochaetae of TC 1 slightly shorter in size than following notochaetae. All notochaetae simple capillaries, arranged in two rows. Neuropodia present as sessile pinnules from TC 6 ( SG 8) to pygidium, with uncini arranged in a single row from TC 7. First thoracic neuropodia ( TC 6) with three or four (6) sharply bent acute tipped, geniculate chaetae. All subsequent thoracic neuropodia with about 8–12 uncini per torus arranged in one irregular row. Uncini as shafted denticulate hooks with long, thin and pointed main fang, straight terminally. Three or four teeth above the main fang, surmounted by a row of four to five short teeth and an upper crest of several smaller denticles ( Fig. 12C ). Abdomen with 25–30 neuropodia as erect pinnules paddle-shaped with entire margin with about 25 uncini; each with four pointed teeth above main fang, surmounted by a row of three to five pointed teeth and an upper crest of minute teeth ( Fig. 12D ).

Three pairs of globular nephridial papillae, located latero-posteriorly to base of each notopodium of TC 1, TC 4 and TC 5 ( Fig. 11D ). Pygidium crenulated, as a funnel-like depression ( Fig. 11A ).

Methyl green staining pattern. Solid to TC 4, with distinct stripes from TC 5 to about TC 11, distinct white antero-ventral lines from TC 5 to TC 9; white glandular region on TC 3 ( Fig. 11 C–D).

Etymology. The species is named after Dr. Jacques Grall, for his many contributions to benthic ecology of maerl beds, for his friendship and his role of mentor for the young generation of French benthic ecologists. Indeed, this species name was chosen in agreement with Vincent Le Garrec and Gabin Droual, from Brest laboratory, who collected many specimens for us and who are supervised by Jacques Grall.

Habitat. Coastal maerl (rhodolith) beds, 1–5 m depth.

Type locality. Bay of Brest , Brittany, France .

Distribution. Bay of Biscay (Bay of Brest), English Channel (Morlaix Bay) ( Fig. 1 ).

Remarks. Terebellides gralli n. sp. is similar to T. parapari n. sp. in having a small size (<20 mm), the presence of a glandular region on TC 3 and the absence of projecting papillae on lamellae of the branchiae. However, these two species can be differentiated by the presence of pointed terminal projections on branchial lobes for T. gralli n. sp. (presence of filaments for T. parapari n. sp.), by the size of notochaetae (longer on the first chaetiger for T. parapari n. sp., slightly shorter for T. gralli n. sp.), the shape of the glandular region (J-shaped for T. parapari n. sp. vs crescent moon-shaped for T. gralli n. sp.) and the presence of a 5 th lobe for T. gralli n. sp. (absence for T. parapari n. sp.). Terebellides gralli n. sp. is also very similar to T. atlantis in having a small size (<20 mm), two pairs of lobes not fused and provided with pointed projections and in lacking projecting papillae on lamellae of branchiae. However, T. gralli n. sp. differs from T. atlantis by the presence of glandular regions both on TC 3 and 5 th branchial lobe ( Table 2 ).

For now, and based on molecular results from Nygren et al. (2018), T. gralli n. sp. seems to be absent from Northern waters.

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 11. Terebellides gralli n. sp. holotype MNHN-IA-TYPE 1874 (A, C–D), paratype MNHN-IA-TYPE 1875 (B) A. Entire worm, lateral view; B. Anterior part, lateral view; C. Anterior part, lateral view, methyl green staining; D. Anterior part, dorsal view, methyl green staining. Abbreviation: glr, glandular lateral region; np, nephridial papillae. Arrow indicates anteroventral band. Scales: A, C=1 mm, B, D=500 µm.

FIGURE 12. Terebellides gralli n. sp. SEM paratype MNHN-IA-TYPE 1876 A. Anterior part, lateral view; B. Anterior part, dorsal view; C. Uncini, thoracic chaetiger; D. Uncini, abdominal chaetiger. Abbreviation: np, nephridial papillae. Scales: A=1 mm, B=500 µm, C–D=0.15 µm.