Narella candidae, Taylor & Rogers, 2017

Taylor, M. L. & Rogers, A. D., 2017, Primnoidae (Cnidaria: Octocorallia) of the SW Indian Ocean: new species, genus revisions and systematics, Zoological Journal of the Linnean Society 181, pp. 70-97 : 85-87

NARELLA CANDIDAE SP. NOV.

( FIGS 2C, 10, 11)

Material examined: Holotype – NHMUK 2016.37 (J C0 6 6- 3 7 4 6), s t a. 8, e v. 2 2, A t l a n t i s B a n k, 32°41′55.177′S, 57°17′40.325′E, 763 m, 13 December 2011. SEM stubs – T170-172 .

Description: Holotype uniplanar with equal dichotomous branching, 31 cm high, 18 cm wide ( Fig. 10a; wider in situ, Fig. 2c), base diameter 4 mm. No holdfast. Axis striated, iridescent green ( Fig. 10g) with darker brown to green nodes which are slightly thickened; axis light gold distally ( Fig. 11l), where just nodes are darkened. Polyps ~ 2.5 mm tall, whorls of 4–6 (higher number on larger-diameter branches), 9–10 whorls per 3 cm of branch ( Fig. 10b), whorl diameter 4.0–5.0 mm.

Polyps with thick, robust sclerites. Basal scales ~ 1.4 mm tall ( Fig. 11f) with rounded distal margin; generally two pairs of adaxial body-wall scales ( Fig. 10d, i) that together do not form a closed basal ring. Sometimes a third smaller scale in centre of basal row ( Fig. 10d, ii). Exterior basal scale surface covered in thick layer of flesh. Medial scales smaller (1.1 mm tall, 0.8 mm wide, Fig. 11g, h), similar shape to buccal scales (1.5 mm tall, 1.4 mm wide), with rounded distal and lateral edges ( Fig. 11g, h). Inner surface of basal, medial and buccal scales have a large sparsely granular area; basally there is a large smooth distal margin ( Fig. 11f, i, j).

Tall operculum, easily seen in lateral view ( Fig. 10c, f). Opercular scales (0.95–1.5 mm tall, 0.4–0.7 mm wide) progressively smaller from adaxial to abaxial. Larger opercular scales with large keel ( Fig. 11b, lateral keel view) and corresponding concaved abaxial surface; smaller opercular less concaved bearing modest keel ( Fig. 11c–e). All opercular scales robust, thick, with a smooth surface; granules to posterior of inner opercular surface small and evenly spread. No tentacular scales noted.

Coenenchymal scales elongate (up to 2.5 mm long), rounded edges forming a mosaic, slab-like coenenchyme ( Fig. 11m) on larger branches; branchlet coenenchymal scales are longer and thinner.

Known distribution: Atlantis Bank, SW Indian Ocean, 763 m depth.

Etymology: Named after Dr Candida Rogers, wife of Prof. Alex Rogers, and suitably also Latin for ‘white’ and ‘radiant’. We present ‘ candidae ’ as a noun in the genitive form as per article 31.1.2 of the ICZN.

Remarks: Colony, or many polyps of the colony, is brooding. No other Narella has been noted as having dark gorgonin nodes or internodes. This phenomenon has evolved independently at least twice in Primnoidae – Mirostenella and Narella (see Fig. 3); and four times in Octocorallia – the above and Isididae (bamboo corals) and Melithaeidae ( McFadden et al., 2006) .

The colony had a resident snake star ( Ophiuroidea: Euryalidae ) attached when collected (see Fig. 2c).

Comparisons: Similar to comparisons of Narella speighti sp. nov., it is here necessary to make comparisons to a number of species which have dichotomous colony branching, or species of unknown branching structure which have polyps that are under 2.5 mm in length. Again, N. cristata , N. parva and N. regularis are not compared as they have lateral crests or ridges on their basal scales which are lacking in N. candidae sp. nov. Basal scales of N. horrida have a pointed distal edge so are also not considered further.

Polyps of N. laxa tend to have four pairs of body-wall scales and a pointed tall operculum with opercular scales that are not concaved. Polyps of N. speighti sp. nov., N. leilae , N. vulgaris , N. obscura , N. clavata and N. japonensis are flared with thin distal edges on medial and buccal scales; this is unlike the rounded, thick, and slight inward curve of these scales in N. candidae sp. nov.

The species most similar to Narella candidae sp. nov. is N. biannulata . Described by Kinoshita in 1907 (a paper we were unable to locate) and re-described, with drawings, in 1908, this species has similar branching structure, polyp size, polyp and whorl density, and scale orientation and ornamentation as N. candidae ; it even has an unusual greenish metallic tinge to its axis. The 1908 description indicates that N. biannulata has coenenchymal scales with outer surfaces that are wrinkly or creased (‘Runzeln’). The specimen presented here as N. candidae has coenenchyme with smooth, rounded outer surfaces. And N. biannulata is described as lacking adaxial buccal or basal scales; N. candidae commonly has two pairs of adaxial buccal scales. For these reasons we propose N. candidae as a new species.

Narella canididae was placed as sister to Narella dichotoma in the phylogenetic analysis. The latter differs in having larger polyps than the former and just one pair of adaxial buccal scales as well as having a bushy, flabellate colony shape.