Dasystenella acanthina ( 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 : 99-102

Dasystenella acanthina ( Wright and Studer, 1889)

Fig. 39

Stenella acanthina Wright & Studer, 1889: 59 , pl. 14, fig. 3, pl. 20, fig. 10

Stenella (Dasystenella) acanthina Versluys 1906: 39 ,48

Thouarella longispinosa Kükenthal, 1912: 299 , figs 1–3

Thouarella (Euthouarella) longispinosa Kükenthal 1915: 151 (in part); 1919: 441 (in part); 1924: 302 (in part); Broch 1965: 26–27, pl. 3 figs 8–10

Thouarella longispinosa Gravier 1914: 61–63 , pl. 7, figs 35–36, pl. 10, figs 52–55; Thomson & Rennet 1931: 24–26; Utinomi 1964: 11–12, fig. 6, pl. 2

Thouarella acanthina Brito 1993: 242–243

Dasystenella acanthina Bayer 1981: 934 , 937, 946 (key to genus); Bayer & Stefani 1989: 454 (key to genus); Cairns 2006: 188–189; Cairns & Bayer 2009: 32 (listed), 47–49, fig. 18 i–p

Material examined: Syntype of Stenella acanthina, NHM 89.5.27.48a, Deutsch Subpolar Expedition 1901–1903, Gauss–Station, off Argentina, 385 m, 12 Jan 1903; Syntype of Thouarella longispinosa, MNHWU and SMF ; USNM 84325, R/V Eltanin, cruise 12, sta. 1083, east of South Orkney Islands, Scotia Ridge, Antarctic , 60°51’S, 42°57’W, 284 m, 14 Apr 1964.

The MNHWU syntype of T. longispinosa is in poor condition with few intact polyps. The SMF sample is in a good condition. Examination of all the polyps confirmed the proposed synonymy. The colony description was taken from Kükenthal (1912) .

Description of Thouarella longispinosa syntype ( MNHWU)

The colony is bottlebrush in branching, with branchlets up to 22 mm long.

The polyps are 1.5–2.0 mm long, distally flared ( Fig. 39c ), and upwardly inclined, in whorls of 3 or 4, rarely in pairs, with 5 whorls per cm. The polyps are covered with a small number of scales in 5 longitudinal rows, reducing to 4 at the polyp base. Each polyp has 4 scales in an abaxial row ( Fig. 39c ), 2 lateral rows, each with 3 scales, and 2 reduced rows of 3 small scales adaxially.

The operculum is tall and conical, composed of 8 elongated isosceles triangle-shaped operculars. The operculars are not evenly spread around the circumference, the 2 reduced inner adaxial operculars being smaller ( Fig. 39h ) than the abaxial operculars ( Fig. 39k ), the latter of which have a proximally diagonal basal edge, depending on their opercular position. The inner surface of all operculars bears a simple, flattened keel. The operculars are 100–430 µm wide (average 260 µm), and 555–970 µm long (average 770 µm). Tubercles cover the proximal half of the inner surface and smaller operculars have fewer tubercles. The outer surface has a slightly concave median longitudinal groove and is usually smooth. Infrequent striations radiate from the central proximal area.

Each polyp has 5 marginals. Three are very long abaxial marginals ( Fig. 39n , similar in shape to large operculars), 530–1340 µm high (average 840 µm), 300–570 µm wide (average 440 µm), with a H:W of 1.3–2.6 (average 1.9). Two of these 3 are outer laterals ( Fig. 39m ) with the remaining 2 small, square to circular-shaped marginals placed adaxially ( Fig. 39b 1 ) and of a similar size to smaller body-wall scales ( Fig. 39f,g ). Large marginals do not fold over the operculum but are upwardly inclined and lean slightly adaxially giving the 2 laterals a diagonal proximal edge ( Fig. 39m, n ). The proximal half of the inner surface is covered in tubercles to the base of the keel, which is channelled. The outer surface is smooth with sparse granules and a modest longitudinal groove.

The body-wall scales can be large (same size as largest operculars) and circular ( Fig. 39e ), 220–500 µm high (average 350 µm), 200–570 µm wide (average 420 µm), with a H:W of 0.8–1.1 (average 0.9). Tubercles cover the inner surface whilst the outer surface is smooth with some granules across the central proximal area of larger scales. Body-wall scales have a finely serrated distal edge.

The coenenchymal scales are small and circular to elliptical in shape ( Fig. 39l ), 150–200 µm wide and high. All sclerites of this species have a coarsely lobate proximal edge.

Distribution

This species is found off Tierra del Fuego , the South Shetland Islands and the South Scotia Ridge between the South Orkney and South Sandwich Islands, from 110–5087 m depth .

Remarks

When Kükenthal (1912) transferred Stenella acanthina to Thouarella he mentioned that it was very similar to T. longispinosa Kükenthal, 1915 . Thomson and Rennet (1931) described T. longispinosa as having 4–5 marginals. Thouarella longispinosa does have five marginals and is thus Dasystenella . Brito (1993) does not explain clearly the inclusion of D. acanthina in Thouarella and we believe this is incorrect based on the lower number of marginals found in D. acanthina .

The specimens of Thouarella longispinosa from MNHWU and SMF differ from the holotype of D. acanthina in having polyps with operculars and marginals more similar in size to each other, although, marginals of the specimens of T. longispinosa are generally longer and have a higher H:W of 2.7, compared to 2.1 in D. acanthina ( Cairns 2006) . However, Cairns (2006) lists some specimens of D. acanthina from southerly latitudes with polyps that are smaller and more upwardly inclined with marginals that have a much higher H:W of 3.5. Given this wide variation and the limited differences between specimens of T. longispinosa and the description of D. acanthina , we propose that T. longispinosa be synonymised with D. acanthina , noting that a revision of Dasystenella is required.

Figures

FIGURE 1. First illustration of Thouarella antarctica (from Valenciennes 1846): a) full colony; b) close up of polyps.

FIGURE 39. Dasystenella acanthina, images from syntype of Thouarella longispinosa (synonymised here with D. acanthina), MNHWU: a) 4.8 cm and 2 cm colony fragments; b) adaxial polyp view; c) abaxial polyp view; d) stereo opercular view; e) outer and f,g) inner body-wall scales; h–k) inner surface opercular scales; l) coenenchymal scales, upper scale outer surface, lower scale inner surface; m) inner and n) outer surface of marginal scales. NB—some operculars are missing. ‘1’ indicates small adaxial marginal scale. Image a) by ZGR.