Thouarella brucei Thomson and Ritchie, 1906

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 : 41-44

6. Thouarella brucei Thomson and Ritchie, 1906

Figs 14 , 15

Thouarella brucei Thomson & Ritchie, 1906: 852–854 , pl. 1 fig. 1, pl. 2 fig. 1; Kükenthal 1919: 439; 1924: 301

Thouarella versluysi Kükenthal, 1907: 202–203

Thouarella (Thouarella) brucei Cairns & Bayer 2009: 27 (listed)

Not Thouarella brucei Broch 1965: 27–28 , pl. 4 (= Digitogorgia sp. )

Material examined: Holotype, NHM 1933.3 .13.130, Scotia (Scottish National Antarctic expedition of 1902–04), Burdwood Bank or Gough Island, 102–182 m, 1 Dec 1903 or 22 April 1904; fragment of holotype, ZMA COEL03574 ; Syntype of Thouarella versluysi, MNHWU, D.T.E. sta. 103, South Africa, 35˚10’S, 23˚2’W, 500 m, two 2.5 cm fragments .

Other material: USNM 1130164, R/ V Eltanin, cruise 22, sta. 1536, west tip of South Georgia, sub-Antarctic, 54˚30’S, 39˚20’W, 659–686 m, 8 Feb 1966, 6 colonies; USNM 98029, R/ V Eltanin, cruise 22, sta. 1536, west tip of South Georgia, Antarctica, 54˚29’S, 39˚22’W, 659–686 m, 8 Feb 1966, 2 colonies (30 cm, 12 cm); USNM 98337, R/ V Eltanin, cruise 21, sta. 290, west mouth of Strait of Magellan , Antarctica, 52˚41’S 74˚35’W to 52˚45’S 74˚28’W, 188–247 m, 6 Jan 1966, 3 colonies; USNM 98195, R/ V Islas Orcadas, cruise 575, sta. 93, South Georgia Island, Antarctic Ocean, 54˚38’48”S, 38˚51’18”W, 261–270 m, 9 Jun 1975, 1 colony .

Description

The holotype is a rigid and sparsely branched colony (not shown). The main stem is robust and stiff although the smaller branchlets are more flexible. The axis is circular in cross-section and light yellow, with side branchlets an even lighter shade.

Branching occurs in up to 4 directions all around the main stem at irregular intervals. The branchlets emanate at 60˚, and are upwardly inclined. Overall colony structure appears more bilateral than bottlebrush as the close-set branchlets curve into one plane. Secondary and tertiary branching of the branchlets is common.

The polyps are isolated, 1.5–2.3 mm high, with some occurring on the main stem, and arising in all directions on branchlets. There are 9–12 polyps per cm, modestly flared distally ( Fig. 14a,c ) and upwardly inclined at 40–45˚. Each polyp has 7 longitudinal rows, with 4–5 scales in the abaxial row and 2–3 in the adaxial.

Two rings, the lower consisting of 4 smaller operculars, the upper of 4 larger operculars, form the operculum. Upper operculars align with the outer ring of marginals whilst the lower operculars align with the inner ring of marginals. The operculars range in size from 390–680 µm high (average of 510 µm), 170–330 µm wide (average of 250 µm), with a H:W of 1.5–2 (average 2). The operculars are arrowhead shaped with a rounded apex ( Fig. 15a–e ). The outer surface of operculars is longitudinally concave with sparse granules ( Fig. 15a,b ). Every opercular has a simple keel on its inner surface and is tuberculate proximally.

The marginals also occur in 2 rings, upper and lower. They are diamond-shaped ( Fig. 15f–h ), 490–760 µm high (average of 635 µm), 350–570 µm wide (average of 470 µm), with a H:W of 1.1–1.7 (average 1.4) in the holotype (smaller sizes in voucher specimens). The inner surface of the marginal scales has a complex multi-keel ( Fig. 15f ) sometimes with a flat central area. The inner marginal surface is tuberculate below the keel base whilst the outer surface has granules at the centre and is smooth towards scale edge.

The submarginals are diamond to oval-shaped, with an arched distal edge ( Fig. 15j,i ), 230–670 µm high (average 440 µm), 230–615 µm wide (average 380 µm) with a smaller H:W than the marginal scales (average of 1.14). The inner surface is tuberculate with a narrow smooth band along the distal edge whilst the outer surface has sparsely placed granules.

The body-wall scales are large ( Fig. 15k–l ), 160–560 µm high (average 320 µm), 160–590 µm wide (average 350 µm), and generally circular to elliptical in shape (average H:W 0.9). The outer surface has granules and small striations at the distal edge and the inner surface is tuberculate. The proximal edge of all the scales above is coarsely lobate; the distal edge is finely serrate.

The coenenchymal scales are circular ( Fig. 15n ) with a diameter of 50–150 µm. The outer surface is covered with sharp-peaked granules and small radial striations and the inner surface is tuberculate.

Distribution

Mid- to southwest Atlantic , off the southern coast of Chile and the Antarctic Peninsula, at depths from 100–686 m.

Remarks

Thouarella versluysi was described by Kukenthal (1907) one year after T. brucei . Kükenthal mentioned that T. versluysi was very similar to T. brucei but offered no explanation. Kükenthal also went as far as listing T. brucei as species dubiae atque incertae sedis in his 1924 key. Thouarella versluysi and T. brucei both have a bottlebrush colony morphology (although T. brucei can appear bilateral it is technically bottlebrush). There was not enough material to determine the colony shape of the T. versluysi syntype, however the original description and colony picture depict a bottlebrush colony ( Kükenthal 1907). Both species have isolated polyps that are upwardly inclined at between 40–60˚ and 4–6 scales in the abaxial row of polyps. Thouarella versluysi has slightly smaller polyps than T. brucei , a slightly lower opercular scale H:W (average of 1.8 versus 2), a higher marginal scale H:W ratio (average of 1.7 versus 1.4), and the abaxial surface of sclerites of T. brucei have more peaked granules. These are very minor differences and not enough, in our opinion, to separate these specimens as individual species; Thouarella versluysi is thus synonymised with T. brucei .

Specimens examined in this study have slightly smaller polyp lengths and, as a consequence, smaller sclerite sizes than the holotype.

Comparisons

The polyps of Thouarella brucei and T. brevispinosa have marginal and opercular scales of an almost identical shape. Thouarella brevispinosa has larger polyps with more scales in the abaxial row than T. brucei (6–8 rather than 4–5) and the branchlets of the former are more tightly placed. More material is required of both species to confirm the differences and similarities listed here.

Thouarella brucei shares a similar bilateral–bottlebrush branching morphology with T. koellikeri , T. bipinnata and T. andeep . However, the polyps of T. brucei are distally flared, similar to those of T. andeep , whereas polyps of T. koellikeri and T. bipinnata are clavate and arranged in an irregular alternate manner. The operculars of the polyps of T. andeep have a smooth inner surface whereas those of T. brucei , whose polyps are also smaller, have a simple keel (see Table 3). Lastly, the polyps of T. brucei have fewer scales in the abaxial row than the polyps of T. koellikeri .

The polyps of T. brucei examined in this study have a similar size and number of abaxial scales as T. hicksoni , although those of T. brucei are larger. Thouarella brucei , however, has polyps with operculars that form a full cone, whereas the operculars of the polyps of T. hicksoni are narrower and do not form an opercular cone. The polyps of the T. hicksoni are also far more clustered.

Figures

FIGURE 14. Thouarella brucei, holotype, ZMA. COEL03574: a) abaxial view of polyp; b) 6.5 cm long fragment of holotype; c) lateral view of polyp; d) stereo opercular view

FIGURE 15. Thouarella brucei, holotype, ZMA. COEL03574: a,b) outer surface and c–e) inner surface of opercular scales; f) inner and g,h) outer surface of marginal scales; i) inner and j) outer surface of submarginal scales; k,m) inner and l) outer surface of body-wall scales; n) coenenchymal scales, top row outer surface, bottom row inner surface. Photo and some SEM by ZGR.