Ophryotrocha cf. lipscombae Lu & Fauchald, 2000

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 : 61-63

Ophryotrocha cf. lipscombae Lu & Fauchald, 2000

Fig. 9

Ophryotrocha lipscombae Lu & Fauchald, 2000: 486 , figs 1–4 (type locality: continental slope 110 miles south of Woods Hole, Massachusetts, NW Atlantic, depth 1830 m).

Material examined

MOROCCO • 1 spec. (formalin); GoC, Mercator MV; 35°17.916′ N, 06°38.709′ W; 354 m depth; 2 Mar. 2008; Stn 64PE284_12750W; wood substratum; DBUA0002284.01 .

PORTUGAL • 51 specs (2 hologenophores, 49 paragenophores; ethanol); WIM, Estremadura Spur; 39°17.295′ N, 10°01.045′ W; 327 m depth; 1 Jun. 2017; Stn PES_ROVL17D01-pick#3W; wood substrata; DBUA0002285.01 .

Description of the material examined in this study

Body robust and compact ( Fig. 9A ), with the same width throughout, only tapering at the pygidium. Largest specimen 2.5mm long and 0.43 mm wide for 38 chaetigers ( Fig. 3 ).All segments with a transversal band of cilia. Prostomium short, broadly rounded, slightly trilobed (more evident in smaller specimens; Fig. 9B ), without eyes. Antennae and palps spherical, very small, may appear to be absent (only visible under the microscope). Peristomium achaetous, with two rings half the length of the following segments. Delimitation between the prostomium and the first ring of the peristomium almost imperceptible. Jaw apparatus dark and relatively large ( Fig. 9B ). Mandibles rod-like; in larger specimens, the anterior end is cut in two levels, with the inner lower level toothed (teeth often worn) ( Fig. 9 C–E); in smaller specimens, the anterior end of mandibulae is mainly straight with small elevations at the outer tips and distinctly toothed ( Fig. 9I ). Maxillae with a pair of falcate forceps ( Fig. 9F ), seven pairs of free denticles (D1–7) ( Fig. 9 G–H) and five pairs of accessory plates ( Fig. 9 ; the fifth plate was lost when detachjing the denticles, Fig. 9 G–H)); forceps with a main fang followed by 1–2 large and several very small teeth ( Fig. 9J ); D1 comb-like, with about 18 large and small teeth alternating ( Fig. 9F ); distal denticles plate-like, with up to 8 large and small teeth irregularly alternating ( Fig. 9 G–H). Parapodia uniramous, with broadly conical acicular lobes, sub-acicular lobes and ovoid dorsal cirri fused to the acicular lobe ( Fig. 9N ); ventral cirri apparently absent. Aciculae slightly protruding in all parapodia. Sub-acicular lobes with harpoon-like protruding acicula with acute tip and subdistal tooth ( Fig. 9M ). Supra-acicular chaetae simple, subdistally serrated, tapering abruptly into a large main fang ( Fig. 9 K–L). Sub-acicular chaetae compound with very short serrated blades abruptly tapering into a main fang; heterogomph shafts distally serrated ( Fig. 9O ). Pygidium with terminal anus and 2 very small ovoid anal cirri.

Remarks

Ophryotrocha lipscombae is only known from its original description based on specimens collected from Woods Hole (NW Atlantic) at a depth of 1830 m ( Lu & Fauchald 2000). This species is considered to be unique among the dorvilleids based on the presence of five pairs of accessory plates associated with the denticles of the maxillae ( Lu & Fauchald 2000). Other distinctive characteristics are the presence of teeth below the main fang of the maxillary forceps and the clear fusion between the prostomium and the peristomium. All these characteristics are present in the specimens from the Estremadura Spur (WIM, NE Atlantic) and the single specimen from Mercator MV (GoC, NE Atlantic) examined in this study. The minor differences registered for the specimens from the NW Atlantic concern features that may have been overlooked or misinterpreted, such as: the absence of distal teeth on the mandibulae of larger specimens, which may be worn (in our specimens these teeth are mostly worn and the ones that are present are difficult to detect); the absence of prostomial palps (in our specimens the antennae and palps are tiny and could only be detected under the optical microscope); the absence of dorsal cirri on parapodia (in our specimens the dorsal cirri appear almost entirely fused with the acicular lobes and thus are difficult to distinguish ( Fig. 9N ); figure 1d of the original description illustrates a similar structure); and the tips of the supra- and sub-acicular chaetae, which in our specimens are more abruptly tapered into a distinct main fang (only visible under high magnification). The phylogenetic analysis segregates this species from the others within the tree ( Fig. 2 ). The two sequenced specimens were from WIM, the K2P value from the H3 alignment between the two specimens is 0.00 and the K2P values to the nearest species in the tree, O. maculata and O. hartmanni , is 0.09. However, there are no DNA sequences for the West Atlantic O. lipscombae specimens to compare with. Furthermore, it was not possible to examine the type material that is deposited in the Smithsonian National Museum of Natural History. If the similarity at the morphological and molecular level is confirmed, then this study extends the geographic and upper limit of the bathymetric distribution of O. lipscombae to the NE Atlantic and to a depth of 327 m.

Ecology and distribution

NE Atlantic specimens: from the Estremadura Spur (West Iberian Margin) to the Gulf of Cadiz (Moroccan Margin) in wood substrata, at 327–354 m depth (present study).

Original distribution of O. lipscombae: NW Atlantic, south of Woods Hole, in sediment, at a depth of 1830 m ( Lu & Fauchald 2000).

Figures

Fig. 9.Ophryotrocha lipscombae Lu &Fauchald, 2000 (DBUA0002285.01). Stereo (A–B) and compound (C–O) microscope images. A. Complete specimen, dorsal view. B. Prostomium of a smaller specimen, ventral view. C. Mandibular and maxillary apparatus, ventral view. D–E. Anterior tip of mandible of larger specimens. F. Maxillary carrier, forceps and basal denticles, dorsal view. G–H. Maxillarydistal denticles and accessory plates from right and left sides, respectively. I. Anterior tip of mandible of smaller specimen. J. Maxillary forceps and basal denticles, dorsal view. K–L. Supra-acicular chaetae, mid-body parapodium.M. Sub-acicular hook, mid-body parapodium. N. Anterior parapodium, posterior view. O. Sub-acicular chaetae, mid-body parapodium. Number 1 refers to free denticle 1.

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

Fig. 2 (next page). Majority rule consensus tree from the Bayesian analyses of a combined dataset with two genes (16S and H3). Posterior probability values near nodes result from the analyses in MrBayes. Taxon names highlighted in bold are new species or new sequences for already described species. Habitat specialization indicated by the text ‘VENT’ for hydrothermal vents, ‘SEEP’ for cold seeps, ‘BONE’ for whale/mammal-falls, ‘WOOD’ and ‘ALFALFA’ for wood- and alfalfa-falls, and ‘FISHFARM’ for the organically-enriched sediments beneath fish farms. Brown bars at the base of a clade indicate a specialization to a chemosynthesis-based ecosystem. Green and blue dots indicate depth distributions shallower and deeper than 200 m, respectively.