Octobranchus lingulatus ( Grube, 1863 )

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 : 155-157

Octobranchus lingulatus ( Grube, 1863)

Figure 2

Terebella lingulata Grube, 1863: 56–57 , pl. 6 fig. 1.— Fauvel, 1927: 290, fig. 101 a–g.— Sardá, 1984: 129, fig. 3.— Hutchings & Peart, 2000: Table 2 .

Octobranchus giardi Marion & Bobretzky, 1875: 87–90 , pl. 10 fig. 21, pl. 11 fig. 21.

Material examined: MNHN-IA-PNT 91, one specimen, incomplete specimen, gravid, Northeast Atlantic Ocean, Brittany, Bay of Brest, station ZC, 48°18’55”N, 4°21’53”W, 5 m depth, May 2018. MNHN-IA-PNT 92, one specimen, complete, Northeast Atlantic Ocean, Brittany, Bay of Brest , station BK, 48°21’28”N, 4°26’38”W, 7 m depth, May 2018 . MNHN-IA-PNT 93, one specimen, complete, Northeast Atlantic Ocean, Brittany, Bay of Brest , station ZC, 48°18’55”N, 4°21’54”W, 1.3 m, October 2016 . MNHN-IA-PNT 94, 3 specimens (2 complete), Northeast Atlantic Ocean, Brittany, Bay of Brest , station ZC, 48°18’55”N, 4°21’54”W, 1.3 m, October 2016 , mounted for SEM. AM W.50785, 3 incomplete specimens, Northeast Atlantic Ocean, Brittany, Bay of Brest , ZC, 48°18’55”N, 4°21’54”W, 1.3 m depth, June 2016 .

Comparative material examined: ZMB Verm Q-5048, Terebella lingulata Grube 1863 , holotype, described from Lussin Piccolo , Croatia, Adriatic Sea .

Description. Specimens very small. Complete specimens ranging from 3.59 to 6.32 mm in length, and 0.39 to 0.88 mm in maximum width in thoracic region. Complete specimens with 19 thoracic segments (16 TC) and between 23 and 24 abdominal neurochaetigers.

Thorax uniformly tapered, narrowing posteriorly, without clear boundary between thorax and abdomen ( Fig. 2A ). Buccal tentacles of two types: longer with ciliated depression on distal end, and shorter bulbous ( Fig. 2 C–D). Prostomium compact; tentacular membrane semicircular, projecting anteriorly ( Fig. 2 A–B). Eyespots present, arranged in two dorsal and two lateral patches, with 8–10 brown eyespots in each patch. Upper lip long, well developed, semicircular; lower lip poorly developed. Peristomium projecting as a bifurcated process, below the lower lip ( Fig. 2A ).

Four similar pairs of branchiae ( SG 2–5), basally thick, terminating in a filiform annulated process ( Fig. 2 B–C). First and fourth pairs inserted more dorsally, second and third pairs inserted more laterally (second pair more lateral than third one) ( Fig. 2C ). Lateral sides of branchiae basally with dense tufts of cilia between rings of the filiform process ( Fig. 2C ).

Lateral lobes present on SG 2–5, as membranous collars. Second segment reduced ventrally, with two small lateroventral lobes ( Fig. 2B ). SG 3 with large lateroventral lobes (auricular shape), connected ventrally by a collar, largely obscure those on second segment; inner surface slightly ridged. SG 4 with a similar, though less well-developed lateroventral lappet, with a well-developed ventral collar. Segment 5 with a small dorsolateral lappet ( Fig. 2B ).

Sixteen pairs of notopodia, on SG 4–19, elongate and well developed, first one always smaller than subsequent ones ( Fig. 2 A–C). Notochaetae of two sizes (n = 9–12), arranged in two rows, bilimbate with small limbus.

Neuropodia present as sessile pinnules from TC 4 ( SG 7) to pygidium, with uncini arranged in a single row along body. Thoracic neuropodia with 6–10 uncini per torus. Uncini acicular with large main fang surmounted by five crests of denticles and beard below main fang ( Fig. 2E ). Abdominal neuropodia, as erect pinnules paddle—shaped, with 10–15 uncini per torus. Abdominal uncini with three rows of teeth above main fang, each row with numerous teeth ( Fig. 2F ).

Nephridial papillae not visible. Pygidium lobulated with two short anal cirri ( Fig. 2A ).

Remarks. We have compared our specimens with the holotype of Terebella lingulata Grube 1863 ( ZMB Verm Q-5048, Zoologisches Museum, Museum für Naturkunde der Humbolt-Universität, Berlin) described from Lussin Piccolo, Croatia, Adriatic Sea. Holotype is in two parts and damaged. There are neither branchiae nor buccal tentacles remaining, and shape of lateral lobes is difficult to observe. Nevertheless, the main characteristics of French material matches with holotype. Our specimens differ only by the size (6.3 mm max instead of 7–10 mm for O. lingulatus ( Hutchings & Peart, 2000) and shape of thoracic uncini and buccal tentacles. Thoracic uncini show beard below main fang which is reported here for the first time for the species. Moreover, a third row of teeth above the main fang of abdominal uncini is present, but visible only under SEM. This denticulation of thoracic uncini has an important taxonomic value and this character should be checked on new material of O. lingulatus from the type locality. Following Fauvel (1927) and Gil (2011), buccal tentacles are of one type, long grooved and spatulate. In French specimens, they are of two types: longer ones with ciliated depression situated on distal end, followed by an array of short bulbous ones (but latter could just be retracted long ones or not fully developed ones). Finally, Hutchings & Peart (2000) based on original figure of Grube (1863), reported that all described species of the genus, except Octobranchus myunnus Hutchings & Peart 2000 , have “all pairs of notopodia of similar size”. This is not the case in either the French specimens of O. lingulatus , or on holotype, on which the first notopodia is always smaller than subsequent ones.

Habitat. In Asparagopsis armata and Posidonia spp. ( Sardá 1984); in Laminaria ochroleuca ( Parapar et al.,1993) , coastal maerl (rhodolith) beds (this study).

Type locality. Lussin Piccolo , Croatia, Adriatic Sea .

Distribution. Northeastern Atlantic Ocean (Madeira, Spain, France) ( Kingston & Mackie, 1980; Parapar et al., 1993; and this study); Mediterranean and Adriatic seas ( Kingston & Mackie, 1980). These new records from Brittany represent a northerly expansion for this species and the first records for French Atlantic waters ( Fig. 1 ).

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 2. Octobranchus lingulatus (Grube, 1863) SEM, MNHN-IA-PNT 94A. Entire worm, lateral view B. Anterior region, lateral view; C. Anterior region, dorsal view; D. Buccal tentacles; E. Uncini, thoracic chaetiger; F. Uncini, abdominal chaetiger. Scales: A=500 µm, B=250 µm, C=125 µm, D=50 µm, E–F=10 µm.