Primnoeides flagellum, Taylor & Rogers, 2017

PRIMNOEIDES FLAGELLUM View in CoL SP. NOV.

( FIGS 2D, 15, 16)

Material examined: Holotype – NHMUK 2016.47 About NHMUK ( JC066-3297 ), RRS James Cook, sta. 5, ev.24, Melville Bank, 38 ° 29′35.476′S, 46 ° 45′36.036′E, 1020 m, 26 November 2011 . Paratypes: NHMUK 2016.49 About NHMUK ( JC66- 3291 ), sta. 5, ev. 24, 38 ° 29′58.220′S, 46 ° 45′37.531′E, 1087 m, 26 November 2011 ; NHMUK 2017.1 About NHMUK , ( JC66- 3527 , 29 cm tall colony) , NHMUK 2016.48 About NHMUK ( JC66- 3564 , 28 cm tall colony), sta. 6, ev. 7, Middle of What seamount, 37 ° 56′37.360′S, 50 ° 27′06.37′E, 1339 m, 2 December 2011. SEM stubs – T152-153 , 157–159 .

Description: Holotype is a 35 cm tall flagelliform colony complete with calcareous holdfast (in situ Figs 2d, 15). Alive colony light yellow, preserved white. Axis light yellow and smooth.

Polyps inclined upwards, whorls of three ( Fig. 15a; towards tip of colony sometimes paired), three whorls per cm ( Fig. 16h). Polyps 3 mm tall, 1.6 mm wide. Polyp abaxial surface covered with 3–4 longitudinal rows of body-wall scales although pattern obscured as body-wall scales are irregularly placed ( Fig. 16f). Operculum mostly hidden beneath marginal scales ( Fig. 16e). Opercular scales tongue-shaped ( Fig. 16a) with smooth outer surface and small patch of tubercles on inner proximal surface.

Marginal and body-wall scales ( Fig. 16b) non-differentiated, circular to wide-elliptical in shape with smooth outer surfaces. Inner scale surface has small area of tubercles proximally and smooth band following scale’s distal edge.

Two layers of coenenchymal scales: outer layer circular, very similar to body-wall and marginal scales ( Fig. 16c, d); inner layer spheroid-shaped sclerites covered in tubercles ( Fig. 16g, i).

Known distribution: Specimens collected from Melville Bank and Middle of What seamounts on the SW Indian Ocean Ridge at 1020–1339 m depth.

Etymology: Named after the Latin for ‘whip’, as this species has a whip-like colony form.

Remarks: The 0.2% genetic variability across five genes (most variation found within 18S and 28S) that separates P. sertularoides from P. flagellum would not be considered enough for many barcoding or species definition studies. However, given the acknowledged low rate of genetic variation in coral mitochondrial DNA ( Shearer et al., 2002) and low genetic variability between other octocoral species ( McFadden et al., 2011), alongside the clear differentiation in colony shape, we believe this distinction is valid.

This species could be the same as that occurring 400–450 m depth off the east coast of Africa, alluded to, but not described, in Williams (1992). Observation of those specimens is required for confirmation.

Comparisons: Primnoeides was a monotypic genus before this description and genus revision. Primnoeides sertularoides has a uniplanar colony with opposite branching, very distinct from the flagelliform colony of P. flagellum . sp. nov. and distinct from both species formerly within Digitogorgia – Primnoeides kuekenthali and P. brochi – which both have a bottlebrush colony branching pattern. In addition, opercular scales of P. flagellum are differentiated from marginal and body-wall scales as they are tongue-shaped; this is not the case in specimens of P. sertularoides .