Polaruschakov omnesae, Bonifácio & Menot, 2019

Bonifácio, Paulo & Menot, Lénaïck, 2019, New genera and species from the Equatorial Pacific provide phylogenetic insights into deep-sea Polynoidae (Annelida), Zoological Journal of the Linnean Society 185, pp. 555-635 : 617-619

POLARUSCHAKOV OMNESAE SP. NOV.

( FIG. 20A–G; TABLES 1, 2, 5)

Type material: Holotype, MNHN-IA-TYPE 1841 ( IFR424 ), complete, length 4.43 mm, width 0.83 mm, 19 segments (including tentacular segment), Equatorial Eastern Pacific Ocean , Clarion-Clipperton Fracture Zone, IOM license area, station 99, collected 4 April 2015, epibenthic sledge epi-net, start 11°2.296′N, 119°40.825′W, end 11°2.612′N, 119°39.512′W, 4398– 4402 m depth, 2529 m trawling distance . Paratype, MNHN-IA-TYPE 1842 ( IFR530-1 ), complete, length 4.16 mm, width 0.81 mm, 20 segments (including tentacular segment), Equatorial Eastern Pacific Ocean , Clarion-Clipperton Fracture Zone, GSR license area, station 117, collected 7 April 2015, epibenthic sledge epi-net, start 13°52.317′N, 123°15.442′W, end 13°52.622′N, 123°14.263′W, 4498–4521 m depth, 3129 m trawling distance .

Description (based on holotype and paratype): Holotype complete, 4.43 mm long and 0.83 mm wide for 19 segments (including tentacular segment), dorsoventrally flattened, posteriorly tapering; colour of live animal not known; ethanol-preserved specimen pale white, slightly translucent.

Prostomium bilobed, wider than long, anterior lobes not developed, conical; frontal filaments absent; median notch between prostomial lobes moderately narrow and moderately deep ( Fig. 20A); eyes absent. Median and lateral antennae absent. Palps smooth, tapering into thin tips, short (reaching segment 3); palpophores not enlarged ( Fig. 20A). Facial tubercle absent. Upper lip with multiple minute folds.

Tentacular segment fused to prostomium, with a pair of short lobes, inserted laterally and slightly below prostomium; without acicula or chaetae; tentaculophores distinct, bulbous, equal sized; styles smooth, tapering into thin tips, short (reaching segment 3), dorsal tentacular style slightly shorter than ventral tentacular style ( Fig. 20A); ventrally to the tentaculophores is a distinct globular pad, located laterally to the mouth. Pharynx not everted in holotype; dissected in paratype (MNHN-IA-TYPE 1842), with seven pairs of distal papillae, subtriangular, equal sized; two pairs of jaws, each one with one main fang, outer margin with a very small, secondary tooth (small elevation; Fig. 20B). Second segment with elytrophores, subbiramous parapodia, chaetae and ventral cirri.

Nine pairs of distinct, knob-like elytrophores present on segments 2, 4, 5, 7, 9, 11, 13, 15 and 17 (all elytra missing).

Cirrigerous segments with distinct, small dorsal cirrophores ( Fig. 20C), inserted subdistally on notopodia; styles smooth, tapering into thin tips, long (slightly longer than tip of neuroacicular lobe); dorsal tubercles absent.

Segment 6 without modification.

Ventral cirri smooth, tapering into thin tips, present from segment 2 to last segment; inserted basally on neuropodia of segment 2, style short (shorter than tip of neuroacicular lobe); in subsequent segments inserted medially on neuropodia ( Fig. 20C), style short (shorter than tip of neuroacicular lobe).

Parapodia subbiramous; notopodia much shorter than neuropodia ( Fig. 20C). Notopodia narrow, subtriangular, tapering into very short acicular lobe, tip of notoacicula not penetrating epidermis. Neuropodia large, subtriangular, tapering into long acicular lobe, tip of neuroacicula not penetrating epidermis. Notochaetae very few (one to three observed), short, slender, slightly curved, with distinct spinous rows on convex side, with blunt tips ( Fig. 20D);notochaetae more slender than neurochaetae. Neurochaetae moderate in number (ten to 15 observed), long, distally flattened to concave, serrated along both margins, with pointed tips ( Fig. 20E, F); slightly stouter in middle of fascicle.

Nephridial papillae absent. Pygidium rounded, not enclosed by last segment; with terminal anus; with ventral papilla, rounded to ovoid ( Fig. 20G). Anal cirri lost, scars not seen.

Morphological variation: Specimens with 19 and 20 segments were found, which share most of the morphological characters given in the species description. However, the holotype shows a minute prostomial peak and a minute ventral papilla on the pygidium, whereas the paratype does not show those peaks but presents a more rounded, small, ventral papilla.

Remarks: Polaruschakov omnesae sp. nov. is more similar to Polaruschakov polaris , with both having notochaetae with blunt tips, a wide notch and fewer chaetae than Polaruschakov reyssi . However, in Polaruschakov omnesae sp. nov. the neurochaetae tips are pointed and the palps are short (reaching segment 3), whereas in Polaruschakov polaris the neurochaetae tips are rounded and the palps are longer ( Table 5). The average K2P distance among Polaruschakov lamellae sp. nov. and Polaruschakov omnesae sp. nov. was high (23.3% for COI and 24.4% for 16S). The presence of minute prostomial peaks could be an artefact of preservation, because its presence cannot be observed in the paratype.

Etymology: This species is dedicated to Emmanuelle Omnes (Ifremer) for her help with laboratory work.

Genetic data: DNA sequencing for this species was successful for COI, 16S and 18S. Both specimens shared 100% of genetic material in COI and 16S. 18S was not successfully sequenced for the paratype. The average K2P distance for intraspecific variation was 0.0% for both COI and 16S.

Distribution: Based on the material examined (two specimens), this species has a restricted distribution within the Clarion-Clipperton Fracture Zone, being sampled in IOM (type locality) and GSR license areas.