Polaruschakov lamellae, 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 : 613-614

POLARUSCHAKOV LAMELLAE SP. NOV.

( FIG. 18A–G; TABLES 1, 2, 5)

Polychaeta sp. EBS12o-Po143 (GenBank KJ736547) Janssen et al. (2015).

Type material: Holotype, MNHN-IA-TYPE 1837 ( IFR151 ), complete, length 8.41 mm, width 1.40 mm, 22 segments (including tentacular segment), Equatorial Eastern Pacific Ocean , Clarion-Clipperton Fracture Zone, BGR license area, station 59, collected 28 March 2015, epibenthic sledge supra-net, start 11°48.201′N, 117°30.500′W, end 11°48.442′N, 117°29.395′W, 4384– 4307 m depth, 2469 m trawling distance . Paratype 1, MNHN-IA-TYPE 1838 ( IFR659-1 - 1 ), complete, length 3.40 mm, width 0.58 mm, 17 segments (including tentacular segment), Equatorial Eastern Pacific Ocean , Clarion-Clipperton Fracture Zone, APEI#3 , station 192, collected 21 April 2015, epibenthic sledge epi-net, start 18°44.807′N, 128°21.874′W, end 18°45.338′N, 128°20.418′W, 4821– 4820 m depth, 2799 m trawling distance . Paratype 2, MNHN-IA-TYPE 1839 ( IFR607 ), incomplete, length 2.06 mm, width 0.67 mm, ten segments (including tentacular segment), Equatorial Eastern Pacific Ocean , Clarion-Clipperton Fracture Zone, APEI#3 , station 192, collected 21 April 2015, epibenthic sledge supra-net, start 18°44.807′N, 128°21.874′W, end 18°45.338′N, 128°20.418′W, 4821– 4820 m depth, 2799 m trawling distance .

Description (based on holotype): Holotype complete, 8.42 mm long and 1.40 mm wide for 22 segments (including tentacular segment), dorsoventrally flattened, posteriorly tapering; live specimen slightly translucent, bluish ( Fig. 18A); ethanol-preserved specimen pale white; chaetae golden.

Prostomium bilobed, wider than long, lobes not developed anteriorly, short, rounded anteriorly, with an abrupt depression connecting to superior lip ( Fig. 18A, B); frontal filaments absent; median notch between prostomial lobes narrow and shallow; eyes absent; a pair of internal white ganglia visible through translucent epidermis (difficult to see). Median and lateral antennae absent. Palps smooth, tapering, thin, short (reaching to segment 3; Fig. 18A, B).

Tentacular segment fused to prostomium, with a pair of short lobes, inserted laterally and slightly ventral to prostomium; without acicula or chaetae; tentaculophores prominent, cylindrical, dorsal longer than ventral; dorsal tentacular style smooth, tapering, thin, short (reaching segment 4; Fig. 18B); ventral tentacular style missing. Pharynx not everted on holotype; dissected in paratype (MNHN-IA-TYPE 1838), with pharyngeal papillae not possible to count, two pairs of jaws, each one with one main fang, outer margin with a small, secondary tooth (small elevation; Fig. 18C). Second segment with elytrophores, subbiramous parapodia, with chaetae and ventral cirri.

Ten pairs of large (largest in anterior segments), spherical elytrophores, present on segments 2, 4, 5, 7, 9, 11, 13, 15, 17 and 19 (all elytra missing).

Cirrigerous segments with prominent dorsal cirrophores (largest in anterior segments); styles smooth, tapering, long (longer than tip of neuroacicular lobe; Fig. 18D); on segment 3 longer than on subsequent segments; dorsal tubercles present, rounded on segment 2, lamelliform on subsequent segments ( Fig. 18D), decreasing in size posteriorly, largest on segment 8, inconspicuous on segment 18 (in paratypes, dorsal tubercles not seen).

Segment 6 with a pair of flattened scale-like structures present ( Fig. 18B); inserted before cirrophore, basally inflated, rounded; distally lamelliform, small, not reaching mid-dorsal line.

Ventral cirri smooth, tapering, present from segment 2 to last segment; inserted basally on neuropodia of segment 2, style long (much longer than tip of neuroacicular lobe); in subsequent segments inserted medially on neuropodia ( Fig. 18D), style short (shorter than tip of neuroacicular lobe).

Parapodia subbiramous, notopodia reduced, much shorter than neuropodia ( Fig. 18D). Notopodia reduced, narrow, subtriangular, tapering into long acicular lobe, tip of notoacicula not penetrating epidermis. Neuropodia large, rectangular to subtriangular, tapering into long acicular lobe, tip of neuroacicula not penetrating epidermis; post-chaetal lobe oval, slightly enlarged. Notochaetae very few (three observed), short, slender, slightly curved, with distinct spinous rows on convex side, with blunt tips ( Fig. 18E); notochaetae more slender than neurochaetae. Neurochaetae moderate in number (26 observed), long, distally flattened to concave, serrated along both margins, with blunt tips ( Fig. 18F); lower neurochaetae shorter, with pointed tips ( Fig. 18G), shorter than upper or middle groups.

Nephridial papillae absent. Pygidium rounded, not enclosed by last segment; with terminal anus ( Fig. 18A). Anal cirri lost, scars not seen.

Morphological variation: All specimens shared the following morphological characters: short palps, chaetae, insertion and length of ventral cirri, slightly enlarged post-chaetal lobe. Although the paratypes are in poor condition, they do not seem to present the lamelliform dorsal tubercles. The tubercles might have been lost or this character could be age dependent, because the holotype has 22 segments whereas the paratypes have 18 segments.

Remarks: The notochaetae and neurochaetae are closer to those present in Polaruschakov species. However, as described above, the lamelliform dorsal tubercles and the very reduced prostomium are unique characters, which allow differentiation of Polaruschakov lamellae sp. nov. from the other species belonging to Polaruschakov ( Table 5).

Etymology: The species name came from Latin ‘ lamellae ’ meaning lamella in plural. It refers to lamelliform dorsal tubercles.

Genetic data: DNA sequencing for this species was successful for COI, 16S and 18S. The specimens shared 100% of genetic material in COI and 18S, and ≥ 99.5% in 16S. The average K2P distance for intraspecific variation was 0.0% for COI and 0.2% for 16S.

Distribution: Based on the material examined (three specimens), this species has a wide distribution within the Clarion-Clipperton Fracture Zone, being sampled in BGR (type locality) and APEI#3 areas.