Terebellides marionensis, Lavesque & Hutchings, 2025

Terebellides marionensis sp. nov.

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Figures 4 View FIGURE 4 and 5 View FIGURE 5

Material examined. Holotype. SAMC-A021296 , Sub-Antarctic Indian Ocean , Prince Edward Islands , Marion Island, off Marion Base , 46.89°S, 37.89°E, August 1984 GoogleMaps . Paratypes. Two paratypes from the same collection site as the holotype, SAMC-A097163 GoogleMaps .

Description. Probably large-size species with incomplete holotype 2.5 mm wide (holotype in several pieces, with abdominal parts). Preserved specimens whitish.

Prostomium compact; eyespots absent; large upper lip surrounding mouth; most of buccal tentacles lost, only remaining few short uniformly cylindrical ones ( Figs 4B View FIGURE 4 ; 5A–B View FIGURE 5 ). Lower lip expanded below upper lip ( Figs 4A– B View FIGURE 4 ; 5A–C View FIGURE 5 ). SG I only visible ventrally (and laterally on SEM paratype) ( Fig. 5A View FIGURE 5 ), SG II ventrally and laterally; following segments with lobes as ventral collars, with elevated anterior margins ( Figs 4B, D View FIGURE 4 ; 5A, C View FIGURE 5 ); lateral lappets on SG III–VIII (TC 1–6) continuing ventrally; absence of dorsal rounded projections on first chaetigers; presence of glandular lateral region on SG V (TC 3), oval shape (not easy to observe depending constriction of segments) ( Fig. 4A–B View FIGURE 4 ).

Branchiae arising as a single structure from SG III, reaching SG VII, as single elongate and annulated mid-dorsal stalk, with two pairs of lobes, almost free from each other, lower pair thinner; anterior branchial projection (5 th lobe) present ( Figs 4A–C View FIGURE 4 ; 5A–B View FIGURE 5 ). Dorsal lobes with about 50 packed lamellae; papillar projections on margins absent and ciliated tufts present; lobes terminating with short pointed tips ( Figs 4A–C View FIGURE 4 ; 5B View FIGURE 5 ).

Thoracic notopodia from SG III (thorax incomplete), first pair reduced, notochaetae from TC1 (SG III) about same size as those from subsequent notopodia. All notochaetae simple capillaries, arranged in two rows, anterior row shorter. Neuropodia as sessile pinnules from TC6 (SG VIII) to pygidium. First thoracic pair of neuropodia (TC 6) with 8–9 sharply bent geniculate chaetae, with rounded tips ( Fig. 5D View FIGURE 5 ), subsequent thoracic neuropodia (from TC 7) with about 10–15 uncini per torus arranged in irregular row, rostrum vs. capitium length ratio RvC =1/0.4, four mid-sized teeth above main fang surmounted by three rows of short denticles and upper crest of several minute denticles ( Fig. 5E View FIGURE 5 ); few abdominal neuropodia remaining, as erect paddle-shaped pinnules, each with about 40 uncini present at margin; rostrum vs. capitium length ratio RvC =1/0.8, four teeth above main fang, surmounted by row of about eight short teeth and two rows of shorter denticles ( Fig. 5F View FIGURE 5 ).

Two pairs of globular nephridial papillae posterior to base of notopodia of SG VI–VII (TC 4–TC 5). Pygidium unknown.

Methyl Green staining pattern: the first 10 segments stain solid; GLR light blue ( Fig. 4A–B, D View FIGURE 4 ).

Etymology. This species name refers to the type locality of this species.

Habitat. Mud to fine sands, coastal, depth unknown.

Type locality. Prince Edward Islands , Marion Island, Sub-Antarctic Indian Ocean.

Distribution. Known from type locality only.

Remarks. Many species of Terebellides have been described from the Sub-Antarctic region (e.g. Schüller & Hutchings 2013) but most of these species were sampled from the deep-sea. Only three coastal species have been described: Terebellides kerguelensis McIntosh, 1885 from Kerguelen Islands and redescribed by Parapar & Moreira (2008), T. longicaudatus Hessle, 1917 from South Georgia and T. paulina ( Grube, 1871) from St Paul and Amsterdam Islands. Terebellides paulina , initially described as Terebella , has been synonymized with Terebellides by Hartman (1959). However, even if the original description is very sparse and without any figures, this species seems to have 44 notopodia (bundles of bristles) and should be referred back to the genus Terebella .

Terebellides marionensis sp. nov. differs mainly from T. longicaudatus and T. kerguelensis by the presence of free branchial lobes, which are fused for about 50 % of their length in the other two other species, and by the absence of dorsal projections on the first chaetigers, which are present on TC1 and TC2 for T. longicaudatus and on TC1–TC5 for T. kerguelensis .

Among the other West African species of Terebellides , T. marionensis sp. nov. is similar with T. kirkegaardi Parapar, Martin & Moreira, 2020 by the absence of dorsal rounded projections on the first chaetigers and by the presence of both a glandular lateral region and a fifth branchial lobe. However, the two species differ by the presence of posterior pointed tips on branchial lobes in T. marionensis sp. nov. and filamentous terminal tips in T. kirkegaardi , and by the first thoracic chaetiger and notochaetae being shorter than the subsequent ones in T. kirkegaardi instead of normal ones in T. marionensis sp. nov.