Thouarella striata Kükenthal, 1907

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 : 44-48

7. Thouarella striata Kükenthal, 1907

Figs 16 , 17

Thouarella striata Kükenthal, 1907: 204–205 ; 1915: 150 (key); 1919: 426–428, text figs 197–201; Broch 1965: 31–32, pl. 7, figs 20–21 (sample not seen)

Not Thouarella striata Nutting, 1912: 69 , pl. 10 figs 2, 2a (sample not seen)

Thouarella stricta Molander 1929: 75 (incorrect subsequent spelling)

Thouarella (Parathouarella) striata Thomson & Rennet 1931: 27

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

Material examined: Holotype, MNHWU, Nr. 57, Bouvet Island, 54°26’S, 3°24’E, 457 m.

Other material: ZMH, R/V W. Herwig, sta. 285, Patagonian Shelf, SW Atlantic, 42˚19’S, 58˚01’W, 825 m, 21 Jun 1966, 2.5 cm fragment; ZMH, R/V W. Herwig, sta. 244, SW Atlantic, 36˚51’S, 54˚01’W, 800 m, 14 Jun 1966.

Description

As only a 2.5 cm fragment of the holotype was examined, the general morphology is taken from the original description ( Kükenthal 1907) and the new specimens listed above. The colonies are branched once or twice and flabellate, with branchlets in a bottlebrush arrangement. The branchlets are mostly simple (rare secondary branching), 25 mm in length, emerging from the main stem at almost 90˚; some branchlets are arranged in one plane.

The polyps are isolated, weakly inclined towards the branchlets at 45–80˚ ( Fig. 16b ) and closely spaced, 14–20 per cm (more densely arranged at branchlet base). They are variable in shape, some clavate, some modestly flared distally (the holotype has distally flared polyps, Fig. 16c,d ), 1.5–2.2 mm high (average 1.85 mm). There are 4–6 scales in abaxial rows ( Fig. 16d ) and 3–4 in the adaxial row.

The operculars are triangle to lanceolate-shaped and acutely pointed ( Fig. 17 a–c ), 520–780 µm high (average 660 µm), 230–350 µm wide (average 295 µm), with an average H:W of 2.3. The inner opercular surface is keeled with the keel often having multiple longitudinal striations ( Fig. 17b,c ) that spread radially from proximal keel area towards lateral edges of the scale. The proximal third of the inner surface is tuberculate. The outer surface is concave longitudinally with low striations radiating from a proximal centre ( Fig. 17a ).

The marginals are arranged in 2 alternate circles of 4, one inner and one outer ( Fig. 16e ), (although this is not consistent), and they are wider than the operculars, 530–680 µm (average 600 µm), and slightly shorter, 520–680 µm (average of 600 µm), with an average H:W of 1. They have a triangular distal area and are more squared proximally than the operculars ( Fig. 17d–f ) and they have a strong, multi-channelled keel with striations perpendicular to the distal edge. The proximal half of the inner surface is heavily tuberculate whilst the outer surface is densely covered with granules, with some scales having shallow radial striations towards the distal edge of the scale ( Fig. 17f ).

The submarginals are shorter than the marginals, 530–540 µm high, 520–700 µm (average 610 µm) wide, with an average H:W of 0.88, and have a modest distal point ( Fig. 17g,h ). The inner surface is tuberculate across the basal four-fifths of the scale, with a band of striations running perpendicular to the distal edge. The outer surface is covered with densely placed granules.

The body-wall scales are generally rounded (average H:W 1; Fig. 17 j–m ) with a pointed arch-shaped distal edge ( Fig. 17k,m ). Some abaxial body-wall scales have a sculpted distal edge ( Fig. 17i ). Body-wall scales are 270–580 µm high (average 428 µm), 240–650 µm wide (average 448 µm), progressively reducing in size from the polyp head to base. The body-wall scales have a heavily tuberculate inner surface, with a smooth band bearing a few ridges perpendicular to the distal edge and the outer surface is covered in granules ( Fig. 17k ). Some scales have deep radial striations running from the central proximal area ( Fig. 17i ).

All the sclerites have an irregular distal edge and the proximal edge is coarsely lobate.

The coenenchymal scales are elliptical to circular-shaped ( Fig. 17n–q ) with serrated edges and are 100–500 µm long. The outer surface is covered in granules or is heavily sculpted ( Fig. 17q ) whilst the inner surface is densely tuberculate.

Distribution

This species has been recorded from the South Atlantic, including Bouvet Island to Burdwood Bank ( Broch 1965) and the Patagonian Shelf at depths from 457– 800 m. Broch’s unconfirmed identification (1965) was from 110 m depth.

Remarks

Thouarella striata has a variable polyp form. The surfaces of scales of the polyps from the holotype, both inner and outer, are deeply striated. Other specimens have finer striations on the outer surface but similar deep striations on the inner.

The specimen from station 244 from ZMH (June 1966) was brooding.

Comparisons

With the number of abaxial scales on the polyps ranging from 4–6, T. striata is comparable to several species, namely T. variabilis , T. brucei , T. pendulina , T. hicksoni , T. bipinnata and T. andeep (see Table 3).

Thouarella variabilis generally has fewer scales in the abaxial row than T. striata and lacks wide triangular marginals and striations on the distal edge of the inner surface of marginal and opercular scales. This lack of striations is the primary difference between T. striata and the other species listed above. In addition, the operculars of the polyps of T. andeep have a smooth inner surface and a rounded distal edge whereas operculars of the polyps of T. striata are triangular with a strong keel. The polyps of T. andeep also have fewer scales in the abaxial row and have accessory operculars, which have so far not been found in specimens of T. striata .

When compared to the polyps of T. striata , those of T. pendulina are smaller and more tightly placed, and the outer surface of the sclerites lack striations. In addition, the colonies of T. pendulina have a true bottlebrush colony shape.

The polyps of T. hicksoni are smaller and more densely arranged than those of T. striata .

Colonies of T. bipinnata are uniplanar whereas those of T. striata have a bushy, bottlebrush shape. The polyps of the former are also clavate.

Figures

FIGURE 16. Thouarella striata, SMF 1966, sta. 285: a) 14 cm long colony. Holotype, MNHWU: b) 2.5 cm long fragment; c) lateral polyp view; d) abaxial polyp view; e) stereo opercular view. Photo b) by ZGR.

FIGURE 17. Thouarella striata, holotype, MNHWU: a) outer and b,c) inner surface of operculars; d,f) outer and e) inner surface of marginal scales; g,h) inner surface of submarginal scales; i) abaxial body-wall scale with sculpted distal edge, j,l) inner surface of circular body-wall scales, k) inner and m) outer surface of body-wall scales; n–p) outer and q) inner surface of coenenchymal scales.