Ophryotrocha scutellus Wiklund, Glover & Dahlgren, 2009

Ravara, Ascensão, Wiklund, Helena & Cunha, Marina R., 2021, Four new species and further records of Dorvilleidae (Annelida, Polychaeta) from deep-sea organic substrata, NE Atlantic, European Journal of Taxonomy 736, pp. 44-81 : 67-70

Ophryotrocha scutellus Wiklund, Glover & Dahlgren, 2009

Figs 11–12

Material examined

MOROCCO • 11specs (plus2cf.)(formalin), 2specs (slide preparation);GoC,Mercator MV; 35°17.916′N, 06°38.709′ W; 354 m; 2 Mar. 2008; Stn 64PE284_12750W; wood substrata; DBUA0002288.01 • 1 spec. cf. (formalin); same locality as for preceding; 3 Mar. 2008; Stn 64PE284_12752A; alfalfa substratum; DBUA0002288.02 • 1 spec. (ethanol); same collection data as for preceding; 19 May 2009; Stn B09- 14b_01W; wood substratum; DBUA0002287.05 • 1 spec. (ethanol), 7 specs (formalin), 3 specs (slide preparation); GoC, Meknès MV; 34°59.091′ N, 07°04.424′ W; 698 m; 20 May 2009; Stn B09-14b_03W; wood substrata; DBUA0002287.03 • 3 specs (ethanol), 1 spec. (formalin); same locality and date as for preceding; Stn B09-14b_03A; alfalfa substrata; DBUA0002287.04 • 4 specs (ethanol), 1 spec. (formalin), 1 spec. (slide preparation, hologenophore); GoC, Darwin MV; 35°23.523′ N, 07°11.513′ W; 1100 m; 19 May 2009; Stn B09-14b_02A; alfalfa substrata; DBUA0002287.01 • 1 spec. (ethanol); same locality and date as for preceding; Stn B09-14b_02C; carbonate substratum; DBUA0002287.02 .

Additional material

PORTUGAL • 6 specs (ethanol); WIM, Setúbal Canyon ; 38°16.856′ N, 09°06.734′ W; 1000 m depth; 22 Aug. 2012; on bone material from a cow carcass; DBUA0001557.01-02 .

SWEDEN • 12 specs (ethanol); coastal Skagerrak ; 58°53.1′ N, 11°06.4′ E; 125 m depth; on bone material from a minke whale carcass; DBUA0002348 .

Description (amended)

Size of WIM and GoC specimens varies within 1.55–2.70 mm long and 0.24–0.39 mm wide for 18–24 chaetigers. Skagerrak specimens are larger, up to 3.60 mm long and 0.75 mm wide for 31 chaetigers ( Fig. 3 ). Body dorso-ventrally flattened, with similar width throughout the body, abruptly ending with pygidium in smaller specimens ( Fig. 11A ) or tapering slightly at posterior end in larger ones. Prostomium broadly rounded, dorso-ventrally flattened, with a transverse ridge between the antennae, without eyes ( Fig. 11A ). Antennae and palps long, digitiform; antennae inserted mid-dorsally on the prostomium; palps inserted laterally. Peristomium achaetous, with two rings slightly narrower and shorter than the following segments. Jaw apparatus heavily sclerotized, well visible through the specimen body, usually with an apparent rhombus shape ( Fig. 11 A–B).The morphology of mandibles and maxillary forceps varies with the specimen size ( Fig. 12 A–J). Mandibles rod-like; smaller specimens with straight and clearly dentate anterior end and long apophyse, well surpassing the cutting edge, with a diagonal connection to the shaft ( Fig. 12A ); with growth, the teeth wear out ( Fig. 12B ) and the cutting edge becomes short and more curved forward, without teeth, the apophyse becomes thicker with an almost vertical connection to the shaft ( Fig. 12 D–E). Maxillae of P-type; forceps falcate, comb-like, slightly wider with up to 20 large teeth on the right side, and narrower with up to 26 thinner teeth on the left side ( Fig. 12 F–G); with growth, the teeth of the left forcep become irregular ( Fig. 12H ) resulting in a clear alternation in size in larger specimens ( Figs 11D , 12 I–J); eleven free denticles (D1–11), D1 similar to forceps (always with even teeth), D2 to D11 shovel-like, D4 to D11 usually directed inwards ( Fig. 11 H–I); carrierlike structure with a toothed ridge on each side near the forceps (see details in Fig. 11D ) and with a posteriorly fimbriate handle ( Fig. 11D ). Parapodia uniramous ( Fig. 11C ); pre-chaetal lamellae of median parapodia very long, cirriform; dorsal and ventral cirri digitiform, long (dorsal longer than ventral); sub-acicular lobes conical, about two-thirds the length of pre-chaetal lamellae in smaller specimens, becoming shorter in larger specimens ( Fig. 12 K–N), with a needle-like acicula ( Fig. 11E ). Chaetae long and stiff; supra-acicular chaetae simple, slightly flattening and tapering distally to a fine tip, very lightly serrated, 7 per fascicle ( Fig. 11G ); sub-acicular chaetae compound with bifurcate, sub-distally serrated shafts, and falcate, very lightly serrated blades ( Fig. 11F ), 7–9 per fascicle. Pygidium with terminal anus, a pair of cirriform anal cirri and a very short (almost imperceptible) median stylet.

Remarks

This species was originally described from a minke whale carcass deployed at a depth of 125 m off Sweden and organically enriched sediments beneath a fish farm in Norway, at a depth of 104 m ( Wiklund et al. 2009). Later, seven specimens of the same species were retrieved from an experimentally implanted cow carcass at the Setúbal Canyon (WIM), 1000 m depth ( Ravara et al. 2015). The present study extends the distribution of O. scutellus to GoC where it occurred associated with experimentally deployed alfalfa and wood substrata and control samples (carbonate cubes), at a depth of 354–1100 m. The specimens from the GoC and WIM are overall smaller than the ones originally described from Sweden and Norway ( Fig. 3 ) and exhibit some variation in the mandibular and maxillary morphology, apparently associated with growth ( Fig. 12 ). However, the larger specimens of the southern locations entirely match the morphology of the northern ones. The morphological identification was furthermore confirmed with molecular analyses for both the larger and the smaller specimens. The specimen from GoC (DBUA0002287.01) sequenced here falls among previously published O. scutellus sequences (Genbank accession numbers GQ415506 and KP731544 -48) with within-species K2P values from the H3 alignment of 0.009–0.01, and a K2P value of 0.10 to the nearest species in the tree, O. chemecoli sp. nov. A similar variability in length and corresponding variation in the mandible morphology has earlier been described for other species, such as O. sadina and O. lusa ( Ravara et al. 2015: figs 15, 25, respectively). Differing from what was stated in the original description, the specimens of O. scutellus studied here have eleven pairs of free denticles (instead of seven) in the maxillary apparatus, and the left forcep of the larger specimens have uneven teeth. These characters were also found in the specimens from off Sweden examined here ( Figs 11–12 ). Thus, the original description is here amended accordingly.

Ecology and distribution

NE Atlantic: from Norway to the Gulf of Cadiz (Moroccan Margin). Found in mammal carcasses, organically enriched sediment beneath fish farms, wood, alfalfa and carbonate substrata, at a depth of 104–1100 m ( Wiklund et al. 2009; Ravara et al. 2015; present study).

Figures

Fig. 11. Ophryotrocha scutellus Wiklund, Glover & Dahlgren, 2009. Stereo (A, C) and compound (B, D–I) microscope images.A–C: DBUA0002288.01; D–G: DBUA0002287.03(L1); H: DBUA0002287.03 (L3); I: DBUA0002348. A. Entire specimen, dorsal view. B. Maxillary apparatus through body tissue, dorsal view. C. Mid-body parapodium, posterior view. D. Maxillae, dorsal view (left forcep and first denticles broken), arrows show details of the teeth ridges at the base of the maxillary carriers. E. Needlelike chaeta of sub-acicular lobe. F. Compound sub-acicular chaetae, mid-body parapodium. G. Supraacicular chaeta, mid-body parapodium. H. Maxillae of a specimen from GoC, dorsal view. I. Maxillae of a specimen from off Sweden, dorsal view. The maxillae in H and I are in the process of moulting, thus including functional and replacement sets. Numbers refer to free denticles.

Fig. 12. Ophryotrocha scutellus Wiklund, Glover & Dahlgren, 2009. Mandibulae, maxillae and parapodial development from smaller to larger specimens. Compound microscope images. A, F, K: DBUA0002288.01 (L5); B, G: DBUA0002287.03 (L3); C, H, L: DBUA0002288.01 (L6); D, I, M: DBUA0002287.03 (L2); E, J, N: DBUA0002348. A–E. Mandibulae, ventral view. F–J. Maxillae, dorsal view. K–N. Mid-body parapodia. The maxillae in G, I–J are in the process of moulting, thus including functional and replacement sets.

Fig. 3. Relationships between the number of segments, body length and body width.