Narella speighti, Taylor & Rogers, 2017

NARELLA SPEIGHTI View in CoL SP. NOV.

( FIGS 6, 7)

Material examined: Holotype – NHMUK 2016.33 About NHMUK ( JC066-3719 ), RRS James Cook, sta. 8, ev. 5, Atlantis Bank, 32°42.862′S, 57°14.666′E, 870 m, 10 December 2011. SEM stubs – T165-166 . GoogleMaps

Description: Holotype has equal dichotomous branching, 11 cm tall. Holdfast has multiple main branches indicating, speculatively, branching may be bushy. Axis straw coloured. Polyps 3–4 per whorl ( Fig. 6d), 6–9 whorls (usually 6–7) per 2 cm of axis ( Fig. 6e), whorl diameter 2.5–3.6 mm. Polyps 2.0– 2.2 mm tall ( Fig. 6c).

Basal scales ~ 1.4 mm tall ( Fig. 7n, o), curved away from polyp body, closed ring adaxially, free distal edge tall and rounded, thin and often broken, sometimes jagged, so is not a smooth cowl. One pair of square to oblong body-wall scales placed adaxially.

Medial scales curved outwards, smooth rounded distal edge ( Fig. 7j, m), ~ 1.5 mm wide and 1.1–1.5 mm tall; inner surface with smooth band across distal third, dense granules basally ( Fig. 7j).

Buccal scales outwardly curved with round, smooth distal edge ( Fig. 7k, l), 1.5–1.6 mm tall and wide; outer surface smooth, inner with smooth band across distal third, dense tubercles basally ( Fig. 7k, l).

Opercular scales reduce in size from abaxial to adaxial side. Abaxial opercular scales ( Fig. 7f, g) large, up to 0.86 mm wide, 0.8–0.86 mm tall. Abaxial opercular scales symmetrical ( Fig. 7g, f); asymmetrical on either side ( Fig. 7h, i), with just one wide lateral wing. Adaxial scales smaller, 0.3–0.5 mm wide, 0.55–0.7 mm tall ( Fig. 7a–e), lanceolate shape. Opercular scales with highly concaved outer surface (mirroring keeled inner surface), distal edge appears notched. No tentacular scales.

Branchlet axis surface uneven as coenenchymal scale edges curve away from branchlet. Coenenchymal scales long, thin, 0.3–1.0 mm length ( Fig. 7p) relatively smooth outer surface, dense tubercles on inner surface, and mosaicked when in situ ( Fig. 6f). One layer of coenenchymal scales.

Known distribution: Atlantis Bank, SE Indian Ocean. 870 m depth.

Etymology: Named after Prof. Martin Speight for his mentorship and support of generations of marine biologists.

Comparisons: Most species of Narella have dichotomous branching. As many species are described from specimens lacking a holdfast or colony fragments, some described as uniplanar may well be bushy so all dichotomously branched species and those with unknown branching patterns were considered if they had polyps ≤ 2.5 mm tall. Narella gilchristi , N.megalepis , N. biannulata , N. horrida , N. bayeri and N. dampieri all have more than four polyps per whorl so were disregarded. Narella clavata has thick mosaic-like coenenchymal scales, very different to those of N. speighti sp. nov. Narella laxa was not considered as it has four pairs of body-wall scales. The outer surface of sclerites of N. speighti are relatively smooth, whereas those of N. parva , N. regularis , N. cristata and N. abyssalis have distinct ridges. Narella leilae has basal scales that form a large, flared cone; unlike the projecting, lobate edges of the basal scales seen in N. speighti . Polyp and sclerite size, structure and orientation look very similar to those of N. obscura . We separate them based on their coenenchymal scales, which are not elongate in N. obscura , as they are in N. speighti . Basal and buccal scales of N. japonensis are more modest than those of N. speighti and the colony branching does not appear to be bushy from the fragment described. The basal scales of N. vulgaris do not have lobate projections; they are more rounded and the sclerites are not as smooth as those of N. speighti . There is also no clear separation of the dense tubercle-covered base on the inner surface of sclerites, something clearly seen in N. speighti . With the above comparisons considered we recommend this specimen as a new species.