Macellicephala brenesorum Neal & Brasier & Wiklund 2018, sp. nov.

Macellicephala brenesorum sp. nov.

(Figure 2E and Figure 11, 12; Table 2.)

Macellicephala sp. B in Neal et al. (2017) [record].

Material examined. Holotype, NHMUK.2018.830, Pine Island Bay, Amundsen Sea, Southern Ocean, cruise JR 179, station BIO5 -EBS-1A, collected on 09/03/2008, epibenthic sledge epi-net, 74°7' 6''S, 105°50'16 W, 1478 m depth.

Description (based on holotype). Medium sized species; holotype complete specimen in a reasonably good condition, 12 mm long, 1.7 mm wide excluding parapodia and 5 mm wide including parapodia, 18 segments (segment 1 = tentacular segment); body dorsoventrally flattened, tapering anteriorly and posteriorly; live specimen not observed; dorsum and everted proboscis purple in alcohol (Fig. 11A), rest of integument pale yellow (Fig. 11B).

Prostomium bilobed with moderately wide and deep median notch; prostomial lobes slightly pronounced, anteriorly tapering (Figs. 2E and 11C). Frontal filaments distinct, slender, slightly enlarged basally, distally tapering (Figs. 2E and 11C). Eyes absent. Facial tubercle trilobed, composed of three inflated squarish lobes, with median lobe slightly larger than lateral lobes (Figs. 2E and 11C). Ceratophore of median antenna prominent, elongated, cylindrical, inserted medially on prostomium (near the base of anterior notch) (Figs. 2E and 11C); style of median antenna very long (extending to segment 9), smooth and slender. Palps thick, smooth, tapering into slender tips; relatively short (extending to the beginning of segment 6).

Tentaculophores large (Figs. 2E and 11C), cylindrical, equal-sized, inserted laterally to prostomium, achaetous; styles still attached on left side only, long, slender, smooth, similar in form, but shorter in length than style of median antenna (about 3/4 for dorsal tentacular cirrus and ½ for ventral cirrus), dorsal cirrus longer than ventral cirrus. Pharynx everted, with 9 pairs of equal-sized triangular papillae distally (Fig. 11D); two pairs of dark amber coloured jaws with smooth margins. Second segment with elytrophores, biramous parapodia, chaetae and ventral cirri.

Nine pairs of prominent, bulbous elytrophores, on segments 2, 4, 5, 7, 9, 11, 13, 15 and 17; all elytra missing.

Parapodia biramous. Notopodia reduced to elongate acicular lobe (Fig. 12A, C), starting on mid-dorsum as two raised ridges, extending into slender elongated acicular lobe, tip of notoacicula not penetrating epidermis; two narrow white lines across dorsum of each segment, connecting raised ridges. Neuropodia large (Fig. 12A), approaching subtriangular to rectangular shape, with elongate slender acicular lobe (Fig. 12B); tip of neuroacicula not penetrating epidermis. Cirrigerous segments with prominent, cylindrical cirrophores, inserted basally on notopodia; styles often missing, remaining styles very long (much longer than tip of neuropodial acicular lobe), smooth slender, similar in form to styles of median antenna and tentacular cirri. Dorsal tubercles present as distinct, conical mound (Fig. 12C). Ventral cirri smooth, slender, tapering; present from segment 2 to last segment; inserted basally on segment 2, where very long, (longer than associated neuropodia lobe); inserted medially on subsequent segments (Fig. 12A), where short (not reaching the distal margin of neuropodial lobe).

Notochaetae missing (broken stumps observed). Neurochaetae numerous (Fig. 12B); all translucent, long and slender of two forms: either slightly flattened subdistally with faint serration along both margins, with blunt tips (Fig. 12D) or subdistal section with margins appearing raised, creating a depression through mid-shaft, margins faintly, but densely serrated, with pointed tip (Fig. 12D).

Nephridial papillae on ventrum of segments 10, 11 and 12 prominent, globular (Fig. 11B), inconspicuous in other segments, present from segment 5. Reduced parapodia of segment 18 lateral to pygidium, consisting of notopodia only. Pygidium conical (Fig. 11E, F). Anal cirri not observed.

Remarks. Of the Southern Ocean Macellicephala species, M. brenesorum sp. nov. is most similar to M. patersoni sp. nov. but differs in having smaller, cylindrical ceratophore of median antenna without pigmentation, in having distinct dorsal tubercules and in the form of pygidium and chaetae (see also Remarks under M. patersoni sp. nov.). For comparison with other known Macellicephala species, including those described in this publication, see Table 2.

Molecular Information. COI (648 bp), 16S (374 bp) and 18S (1804 bp) were obtained from the holotype. Based on 16S, this species was closest to Macellicephala patersoni sp. nov. with uncorrected 'p' distance 0.156.

Etymology. Macellicephala brenesorum sp. nov. is named after the first author's wonderful friends Hana and Fernando Brenes, who assisted with the image editing for this publication, while their lovely daughters Adira and Tzofia provided their very own rendition of the well-known nursery rhyme, which now goes: “There is a worm at the bottom of the ocean.”

Distribution. Known only from its type locality, Pine Island Bay, Amundsen Sea, Southern Ocean, depth of 1478 m.