Thouarella grasshoffi 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 : 91-92

25. Thouarella grasshoffi Cairns, 2006

Thouarella (Euthouarella) grasshoffi Cairns, 2006: 184–188 , figs 1a, 12, 13; Cairns & Bayer 2009: 28 (listed)

Material examined: Holotype, USNM 1078188, Manning Seamount , North Atlantic Ocean, 38˚08.74’N, 61˚05.473’W, 1458 m, 16 May 2004.

Other material: all lots from Cairns (2006).

Description

Description modified from Cairns (2006):

The colonies consist of 1–3 main branches from which numerous closely spaced (usually less than 2 mm apart) branchlets originate on all sides of the main branch, in a bottlebrush arrangement. The branchlets are undivided, up to 4 cm long and flexible in tension. The holotype is a single main stem 35 cm long and 8–9 cm wide that has been broken from its base. The axis is 2.4 mm in diameter and is a brownish colour.

The polyps of the holotype occur randomly on the main stem and in regular pairs (10–20% of polyp projections are whorls of 3) every 1.5–1.9 mm on branchlets. They are modestly distally flared, curved upward toward branchlet tip, and are rarely greater than 1.3 mm in length and 0.7 mm in diameter. The sclerites are in 6–8 longitudinal rows with 5–7 scales in the longitudinal abaxial rows.

The operculars form a tall cone and are isosceles triangle-shaped with a pointed apex, 260–620 µm high but most are 450–550 µm, with a H:W of 2.1–3.2. The proximal quarter of the inner surface is tuberculate, the distal half bearing a multi-keel. The outer surface has granules radiating from the central proximal area.

The marginal scales are not arranged in 2 defined rings, as in most Thouarella species , but as 2 sets of 3 with both lateral edges overlapping those of the adjacent marginal and the 2 remaining marginals with one lateral edge above and the other below their adjacent marginal. The marginals have an acutely pointed tip with a broad base, with a H:W of 0.93–2.1 and are up to 540 µm long. The proximal half of the inner surface is tuberculate, the distal half bears 1–3 modest longitudinal keels, sometimes bearing lateral projections. The outer surface is covered in granules.

The submarginal scales are rounded, up to 340 µm high, almost elliptical, and broader than high (H:W of 0.65–0.89). The adaxial scales are rarely larger than 220 µm. Some of the submarginals have a small point at the distal edge and a corresponding small ridge perpendicular to the distal edge on the inner surface. The inner surface of both these and the body-wall scales has a smooth band along the distal edge and tubercules occur across the proximal three-quarters of the scales. The outer surface of the sclerites is smooth with a few granules proximally. The distal edge of all polyp sclerites of this species is finely serrate with a coarsely lobate proximal edge.

The coenenchymal scales are elliptical to elongate in shape, rarely more than 320 µm high with a H:W of 1.3–1.8. These scales have a tuberculate inner surface and a slightly concave, smooth outer surface, sometimes with rare granules.

For images see Cairns (2006).

Distribution

This species is found in the western Atlantic, on the New England Seamount Chain; at depths from 814–1458 m. It also occurs in the eastern Atlantic including off the Cape Verde Archipelago, the Great Meteor Seamount, the Azores Archipelago and the Celtic Sea, at depths from 720–1760 m.

Comparisons

Thouarella grasshoffi is unique within Group 2 in having a true bottlebrush colony shape ( T. hilgendorfi does have bottlebrush branches but has a wider, flabellate colony shape, see Table 3). The placement of the branchlets of T. laxa is pinnate but can appear bottlebrush because its flexible branchlets can be curved. The polyps of T. laxa are a similar size with similar spacing as those of T. grasshoffi , however, the former has a low opercular cone and shorter operculars with a blunt distal edge, whereas T. grasshoffi has a tall opercular cone, reflected in tall, triangular operculars. There is also a geographical separation between the two species with T. grasshoffi being found in the North Atlantic and T. laxa in the Indo-West Pacific.

Most species within Group 2 have polyps that are distally flared whilst Thouarella grasshoffi and T. moseleyi have more rounded, clavate polyps. The latter species differs from the former in having polyps with shorter marginals and a colony with a pinnate branching arrangement (so the colony can appear bilateral), whereas T. grasshoffi has a bottlebrush colony form.

Recent and new species combinations