Nu aakhu Bonifácio & Menot 2019, GEN. NOV., SP. NOV.

(FIG. 17A–F; TABLES 1, 2)

Type material: Holotype, MNHN-IA-TYPE 1836 (IFR341), complete, length 4.82 mm, width 0.76 mm, 18 segments (including tentacular segment), Equatorial Eastern Pacific Ocean, Clarion-Clipperton Fracture Zone, GSR license area, station 117, collected 7 April 2015, epibenthic sledge supra-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): Holotype complete, 4.82 mm long and 0.76 mm wide for 18 segments (including tentacular segment), dorsoventrally flattened; slightly tapering posteriorly; live specimen translucent, bluish; digestive system and chaetae internally visible, chaetae golden (Fig. 17A); ethanolpreserved specimen pale white, translucent.

Prostomium bilobed, wider than long, lobes not pronounced, short, anteriorly rounded; fused with tentacular segment; frontal filaments absent; median notch between prostomial lobes shallow and moderately wide (Fig. 17A, C); eyes absent. Median and lateral antennae absent. Palps smooth, tapering, short (reaching segment 3), with small, distinct palpophores (Fig. 17C). Facial tubercles absent. Upper lip with minute folds.

Tentacular segment fused to prostomium, with short lobe, inserted ventrolaterally to prostomium; without acicula or chaetae; tentaculophores very short, small, distinct, equal sized; tentacular styles short, smooth, tapering distally into filamentous tip; dorsal tentacular style (reaching segment 4) slightly longer than ventral tentacular style (Fig. 17C). Pharynx not everted. Second segment with elytrophores, subbiramous parapodia, with chaetae and ventral cirri.

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

Cirrigerous segment with distinct, small dorsal cirrophores (Fig. 17D), inserted basally on notopodia; styles smooth, tapering, long to short (anteriorly, longer than tip of neuroacicular lobe; posteriorly, about as long as tip of neuroacicular lobe); dorsal tubercles absent.

Segments 5 and 6 with large, swollen dorsal structure (Fig. 17A, B), interiorly whitish; smaller, bilobed on segment 5 (maybe because of elytrophore), larger on segment 6. Elytrophore not visible on segment 5 because of swelling.

Ventral cirri smooth, tapering, present from segment 2 to last segment; inserted basally on neuropodia of segment 2, style long (longer than tip of neuroacicular lobe); in subsequent segments inserted subdistally on neuropodia (Fig. 17D), styles short (shorter than tip of neuroacicular lobe); on segments 3 and 4 shorter than those in posterior body; on segment 5 longer (approaching tip of neuroacicular lobe).

Parapodia subbiramous (Fig. 17D). Notopodia very reduced to small, pointed acicular lobe, tip of notoacicula not penetrating epidermis. Neuropodia large, subtriangular, tapering into elongate acicular lobe, tip of neuroacicula not penetrating epidermis. Notochaetae absent. Neurochaetae moderate in number (16 observed), short to long, distally flattened to concave, with pronounced, widely spaced spines along both margins, with rounded tips (Fig. 17E, F); often, middle group with single, stouter neurochaeta.

Nephridial papillae absent. Pygidium rounded, not enclosed by last segment; with terminal anus (Fig. 17A). Anal cirri lost, scars not seen.

Remarks: As detailed in the genus section, Nu aakhu gen. nov., sp. nov. is unique in not having notochaetae and in having very short notoacicular lobes, very small elytrophores and neurochaetae with prominent spines along both margins.

Etymology: Again, in the ancient Egyptian religion, ‘ áakhu ’ is one of the elements that compose the human soul. An ‘ áakhu ’ is the glorified spirit or a blessed soul which has passed the final judgement (the Weighing of the Heart). The term refers to the translucent character of the body of this worm.

Genetic data: DNA sequencing was successful only for 18S but not for COI or 16S.

Distribution: Only one specimen was sampled at a single station within the Clarion-Clipperton Fracture Zone in GSR license area (type locality).