Primnoa bisquama, Taylor & Rogers, 2017

PRIMNOA BISQUAMA View in CoL SP. NOV.

( FIGS 2B, 12, 13)

Material examined: Holotype – NHMUK 2016.38 About NHMUK ( JC066-960 ), RRS James Cook, sta. 4, ev. 9, Coral seamount, 41°21′20.103′S, 42°55′8.423′E, 952 m, 14 November 2011 ; Paratype: NHMUK 2016.39 About NHMUK ( JC066-3518 ), sta. 6, ev. 7, Middle of What seamount, 37°56′37.200′S, 50°27′06.450′E, 1339 m, 2 December 2011 ; NHMUK 2016.40 About NHMUK ( JC066-3568 ), sta. 6, ev. 7, Middle of What seamount, 37°56′36.986′S, 50°26′46.044′E, 1309 m, 2 December 2011 ; NHMUK 2016.41 About NHMUK ( JC066-3569 ), likely a fragment of NHMUK 2016.40 About NHMUK ( JC066-3568 ). SEM stubs – T154-156 .

Description: Holotype is a 15 cm tall colony, light pink in vivo (in situ Fig. 2b), white once preserved ( Fig. 12a). Colony uniplanar with infrequent dichotomous branching. Axis near black in colour towards base with gold iridescent hue towards branchlet tips.

Polyps isolated, downward facing (as is typical of this genus; Fig. 12b), slightly flared ( Fig. 12c), appressed against branchlets, 2.0–4.0 mm tall (usually around 3.0–4.0 mm, Fig. 12b). Polyps placed 3–5 per centimetre.

Operculum well-developed, low in height ( Fig. 12c). Opercular scales tongue-shaped with small, modest keel ( Fig. 13a); some nearly flat ( Fig. 13c). Adaxial opercular scales slightly smaller than abaxial. Outer surfaces smooth ( Fig. 13b, d). Small tentacular rods abundant, 100–300 μm in length, 50 μm wide ( Fig. 13e, same scale as surrounding scales; Fig. 13s close up).

Majority of polyp body covered by three pairs of large abaxial scales ( Fig. 13j, k; two being marginal scales, Fig. 13f–i); basal pair of scales ( Fig. 13m, l) slightly smaller than marginal scales ( Fig. 13f–i) and separated by a number of small irregular-shaped sclerites ( Fig. 13n, p). No clear adaxial rows of body-wall scales as polyp appressed against branchlet, meaning adaxial marginal scales are often mistaken for coenenchyme.

Marginals near square in shape with rounded distal edge (no marginal spine) and irregular basal edge (most pronounced in Fig. 13h). Four large marginal scales ( Fig. 13f–i) surround 270 ° of opercular opening ( Fig. 12d); remaining diameter with 2–4 smaller (usually 4, although they are sometimes missing) marginal scales of similar shape. Body-wall scales held together by flesh embedded with small irregularly shaped body-wall scales ( Fig. 13r).

All above sclerites have a smooth to granular outer surface and are tuberculate across majority of inner surface. Marginal scales have wide smooth band across distal edge of inner surface ( Fig. 13h). Basal edges of sclerites finely serrate; distal edges relatively smooth.

Elongated, irregularly shaped coenenchyme of variable length, commonly up to 800 μm ( Fig. 13o, in situ at base of Fig. 13p,q).

Known distribution: SW Indian Ocean: Coral and Middle of What seamounts, 952–1339 m depth.

Etymology: The name is formed from a combination of the Latin for ‘double’, bi-, and ‘scale’, squama – in reference to the two pairs of body-wall scales that distinguish this species from other Primnoa . We treat squama as a noun in the apposition and it therefore retains the feminine gender.

Remarks: Previous species of Primnoa have been found from the northern boreal Atlantic, North and East Pacific, Japan and sub-Antarctic areas of the south Pacific.

Comparisons: Primnoa bisquama sp. nov. is distinguished from the remaining four species and one variety of Primnoa (see Cairns & Bayer, 2005) in its low-rise operculum, infrequent polyp placement and relatively modest polyp size. Lacking a marginal spine and having a squat polyp means this species is most similar to P. notalis and P. resedaeformis . Primnoa bisquama differs from both these species in having fewer pairs of body-wall scales: just two pairs of large body-wall scales (in addition to a large pair of abaxial marginal scales) with a variable number of smaller scales in the basal abaxial polyp area, rather than four (or more) pairs of body-wall scales.