Thouarella bipinnata Cairns, 2006

TAYLOR, M. L., CAIRNS, S. D., AGNEW, D. J. & ROGERS, A. D., 2013, <strong> A revision of the genus <em> Thouarella </ em> Gray, 1870 (Octocorallia: Primnoidae), including an illustrated dichotomous key, a new species description, and comments on <em> Plumarella </ em> Gray, 1870 and <em> Dasystenella </ em>, Versluys, 1906 </ strong>, Zootaxa 3602 (1), pp. 1-105 : 67-68

13. Thouarella bipinnata Cairns, 2006

Thouarella bipinnata Cairns, 2006: 176–181 , figs 8, 9; Cairns & Bayer 2009: 28 (listed)

Material examined: Holotype, USNM 53015, Gerda 177, Straits of Florida , off northwest corner of Little Bahamas Bank, 27˚17’N, 79˚34’W, 686 m depth, 30 Jun 1963.

Other material: all other specimens are from the original description ( Cairns 2006).

Description

Description modified from the original ( Cairns 2006).

Colonies are uniplanar, delicate, and irregularly pinnate to bipinnate (occasionally 2 branchlets occur contiguously on the same side of the stem). The largest specimen (the holotype) is 9 cm long and 10 cm wide with a basal axis diameter of 1.6 mm. The holotype has 4 larger diameter branchlets near the colony base, each with a series of smaller branchlets, up to 30 mm long, that are placed roughly alternately at intervals of 5–15 mm. The axis is golden-yellow colour with a white calcareous discoidal holdfast.

The polyps occur on the main stem and branchlets in a roughly alternating arrangement. Occasionally 2 polyps are arranged opposite to each other but there is no consistent tendency towards pairing or whorls. The polyps of the holotype are orientated toward one face of the colony, with a density of 11–14 per cm, they stand perpendicular to the branchlet, are modestly clavate, and up to 2.4 mm high with a H:W of 1.8–2.2. Each polyp has 6–8 longitudinal rows of scales with 3–5 in the abaxial row. The scales increase in size proximally as the polyp diameter decreases such that at the polyp base there are no adaxial scales and the inner-laterals are either reduced or absent.

The operculars are lanceolate to arrowhead-shaped, up to 900 µm high, with a H:W of 2.1–2.9, and form a well-defined operculum. The outer surface has radial striations from the proximal centre and a deep depression, corresponding to a large simple keel on the inner surface, the keel having many adjacent striations. Tubercules cover the proximal third of the inner surface of the opercular scales.

The marginals are arranged in inner and outer rings of 4 scales each with their distal edges overlapping. The marginal scales are the same size as the operculars but more rounded proximally and have a pointed distal edge and a lower H:W of 1.3–2.1. The inner surface bears a complex keel with wide lateral projections whilst the remaining inner surface area is tuberculate with a narrow smooth distal band along the lateral edges. The outer surface has low radial striations from the proximal centre and some granular markings.

The submarginals are elliptical, with a short, pointed distal edge, and are 500–600 µm high with a H:W of 0.9–0.95. The inner surface is tuberculate with a wide smooth edge distally and some ridges perpendicular to the edge whilst the outer surface is mostly smooth with rare granules arranged radially from the proximal centre.

The body-wall scales are roughly rectangular, sometimes rounded, usually broader than wide (H:W of 0.85–0.9), and can be 800 µm wide towards the polyp base. The proximal outer surface is covered in granules and sometimes striations. The inner surface is tuberculate, often with ridges perpendicular to the distal edge. As with all polyp sclerites of this species, the distal edge is finely serrate and the proximal edge coarsely lobate.

The coenenchymal scales are irregular shaped, up to 600 µm in diameter, and have a highly concave outer surface.

For images see Cairns (2006).

Distribution

Blake Plateau, off northern Florida, and Straits of Florida, off Little Bahamas Bank, to Guyana, from depths of 507–1000 m.

Comparisons

Thouarella bipinnata is the only species within Group 1 that is truly uniplanar with bipinnate to pinnate branching. There are several species that can appear bilateral e.g. T. koellikeri , the colonies of which also have roughly alternating polyps of a similar size to T. bipinnata . However, the polyps of T. koellikeri are more rounded, there are double the number of scales in the abaxial rows (7–10, rather than 3–5 in T. bipinnata ), and polyps of T. koellikeri have a lower opercular cone than those of T. bipinnata . Thouarella affinis and T. viridis have colonies that can both appear bilateral, however, the polyps of both have more scales in the abaxial rows (6–7) than T. bipinnata . Thouarella brucei and T. andeep can have a bilateral colony shape and both have 4–5 scales in the abaxial rows of polyps, comparable to T. bipinnata . However, T. bipinnata has modestly clavate polyps, very different from the distally flared polyps of T. andeep and T. brucei .