Thouarella brevispinosa Wright and Studer, 1889

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 : 30-33

3. Thouarella brevispinosa Wright and Studer, 1889 , new rank

Figs 8 , 9

Thouarella variabilis var. brevispinosa Wright & Studer, 1889: 69 ; Thomson & Henderson 1906: 38 (list); Molander 1929: vol. 2, 74–5

Thouarella (Thouarella) var. brevispinosa Cairns & Bayer 2009: 27 (listed)

Material examined: Holotype, NHM 89.5.27.54, 12 cm, H.M.S. Challenger, sta. 145A, 46°41’S, 38°10’E, off Prince Edward Island , 566 m, 27 Dec 1873.

Other material: ZMH, R/ V W. Herwig, sta. 245, SW Atlantic, 36°49’S, 54°02’W, 550 m, 14 Jun 1966 .

Description

The holotype consists of a single branch ( Fig. 8a ). The branchlets are mostly simple (some secondary, and even tertiary branching), the longest being 25 mm, arranged around the main stem in at least 4 directions, in a bottlebrush formation.

The polyps are large, 2.5–3 mm high, and isolated on branches and branchlets at wide intervals of 7–11 per cm. They are inclined at 60˚ and distally flared with splayed marginals ( Fig. 8b–d ). Each polyp has 6–7 scales in the abaxial row ( Fig. 8c ) and 7 longitudinal rows reducing to 4 at the polyp base. Scales of 4 categories cover each polyp: 8 operculars, 8 marginals, pointed submarginals and a variable number of body-wall scales.

The tips of the operculars meet in an apex to form a cone. The operculars are lanceolate, or isosceles triangleshape with a squared proximal edge ( Fig. 9f,g ), to arrowhead shape ( Fig. 9a–e ; although sometimes they have a rounded distal edge, Fig. 9f,g ). They are 270–770 µm high (average 540 µm) and 200–410 µm wide (average 310 µm), with a H:W of 1.2–2.1 (average 1.7). They have a single, large simple keel on the inner surface that is sometimes channelled with small lateral striations running parallel ( Fig. 9a ). The proximal half to third of the inner surface is tuberculate; the outer surface is longitudinally concave towards the distal edge and there are sparse granules and occasional fine striations in a radial pattern from the proximal area.

Marginals are 510–830 µm high (average 730 µm), 490–600 µm wide (average 530 µm), with a H:W of 1.0–1.6 (average 1.4). They have a broad angular base ( Fig. 9i,j ) and a central triangular distal projection ( Fig. 9h ). The inner scale surface is keeled, the keel having a single channel running longitudinally from the scale centre. There are 2–3 ridges parallel to the keel (more developed than in operculars) and tubercules cover the proximal area with a smooth band distally that has infrequent small ridges perpendicular to distal edge. The outer marginal surface has rows of granules radiating from the centre of the scale.

Generally there are 2 circlets of abaxial and lateral submarginals; the submarginals have a pointed distal edge ( Fig. 9l–n ) and a reduced keel on the inner surface ( Fig. 9k, l ). The adaxial submarginals have a more rounded distal edge, more typical of body-wall scales ( Fig. 9k ). Submarginals are wider than marginals, 550–690 µm (average 610 µm), 450–620 µm high (average 540 µm), with a H:W of 0.8–1.0 (average 0.9). The inner surface is tuberculate and the outer surface has sparse granules sometimes spread radially towards distal edges ( Fig. 9m ).

Body-wall scales are elliptical to circular ( Fig. 9o–s ) and similar in size to submarginal scales; their distal edge curves gently away from the polyp body. The inner surface is covered in tubercles and the outer surface with sparse granules; the proximal edge can also be covered in tubercles. The distal edges of all sclerites of this species are finely serrate; the proximal edges are irregularly lobate.

Coenenchymal scales are oval to round or angular in shape ( Fig. 9t ), 100–200 µm long or wide, with very sparse, irregular, granules on the outer surface; the inner surface is tuberculate.

Distribution

Known only from two locations: the type location off Prince Edward Island , and east of Buenos Aires, Argentina, approximately 7300 km away. Depth range is 550–566 m.

Comparisons

Colonies of T. variabilis var. brevispinosa have larger polyps with more scales in the abaxial row than those of T. variabilis . The former also has sparser branching and taller operculars with a more complete opercular cone than the latter. We thus propose this variety to be elevated to species rank, namely Thouarella brevispinosa .

The polyps of T. brevispinosa are distally flared and a similar size to the polyps of T. antarctica (comparison is made previously), T. striata , and T. affinis which are thus compared below.

The polyps of T. affinis have a similar number of scales in the abaxial row as those of T. brevispinosa , however, the majority of polyps in the latter have taller marginals that are more acutely elongate than the former, whose marginals are modestly pointed.

The size and shape of the marginals of polyps of T. brevispinosa and T. striata are very similar, however the inner surface of the marginals of the latter have robust striations flanking the keel whereas the former have fine striations. Sclerites of T. striata are thick; those of T. brevispinosa are more delicate. Also, tubercles on the scales of T. striata are more densely arranged and the polyps tend to be smaller.

The polyps of T. brevispinosa have fewer scales in the abaxial row than those of T. koellikeri and the abaxial marginals are taller and wider, creating a more flared polyp shape whereas the polyps of the latter are smaller and clavate.

Figures

FIGURE 8. Thouarella brevispinosa, holotype, NHM89.5.27.54: a) 12 cm colony; b) lateral polyp view; c) abaxial polyp view; d) stereo opercular view.

FIGURE 9. Thouarella brevispinosa, holotype, NHM89.5.27.54: a,d–f) inner and b,c,g) outer surface of opercular scales; h) inner and i,j) outer surface of marginal scales—the lateral and distal edges of j are eroded; k,l) inner and m,n) outer surface of submarginal scales; o–q) outer and r,s) inner surface of body-wall scales; t) coenenchymal scales—inner surface on top right and bottom three right scales, remainder show the outer surface.