Thouarella parachilensis, TAYLOR & CAIRNS & AGNEW & ROGERS, 2013

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 : 72-76

17. Thouarella parachilensis sp. nov.

Figs 28 , 29

Material examined: Holotype, USNM 98338, R/ V Islas Orcadas, cruise 575, sta. 90, South Georgia Island, sub- Antarctic, 54˚50’36”S, 37˚23’48”W, 223–227 m, 7 Jun 1975, 1 colony ; Paratype: USNM 98190 ( SEM images), R/ V Professor Siedlecki, cruise 86–01, sta. 121, 53˚57’S, 38˚10’W, South Georgia Island, sub-Antarctic, 90–100 m, 6 Dec 1986, 1 colony ; Paratype, ZSL SG09 , Ev. 35, 53˚44.07’S, 37˚14.58’W, NW of South Georgia Island, sub-Antarctic, 125 m, 18 Jan 2009 .

Other material: USNM 84341, R/V Professor Siedlecki, cruise 86–01, sta. 122, 53˚55’S, 38˚03’W, South Georgia Island, sub-Antarctic, 119–130 m, 16 Dec 1986; USNM 97951, R/V Islas Orcadas, cruise 575, sta. 12, 53˚38’12”S, 37˚54’42”W, South Georgia Island, sub-Antarctic, 130–137 m, 13 May 1975; USNM 98087, R/V Professor Siedlecki, cruise 86–01, sta. 19, 54˚02’S, 39˚06’W, South Georgia Island, sub-Antarctic, 212–224 m, 2 Dec 1986; USNM 98387, R/V Hero , cruise 721, sta. 1144, Bismarck Strait, Anvers Island, Palmer Archipelago, Antarctic Peninsula, 64˚52’09”S, 63˚50’09”W, 440–480 m, 14 Mar 1972; USNM 98361, R/V Hero , cruise 731, sta. 1884, Quintana Island, Wilhelm Archipelago, Antarctic Peninsula, 65˚06’12”S, 64˚59’51”W, 100–180 m, 3 Mar 1973; USNM 98104, R/V Professor Siedlecki, cruise 86–01, sta. 9 and 10, Shag Rocks, South Georgia Island, sub-Antarctic, 53˚3’S, 41˚57’W, 133–165 m, 30 Nov 1986; USNM 98173, R/V Eltanin, cruise 22, sta. 1536, west tip South Georgia Island, sub-Antarctic, 54˚30’S, 39˚20’W, 659–686 m, 8 Feb 1966; USNM 98085, R/V Eltanin, cruise 12, sta. 993, west of Aspland Island, South Shetland Islands, Antarctic Ocean, 61˚25’01”S, 56˚31’01”W, 300 m, 13 March 1963; USNM 98159, R/V Hero , cruise 731, sta. 1944, Neumayer Channel, Anvers Island, Palmer Archipelago, Antarctic Peninsula, 64˚46’40”S, 63˚25’33”W, 100–150 m, 11 Mar 1973.

Etymology

The name refers to Thouarella chilensis , for which this species was often mistaken.

Description

The colonies are flabellate ( Fig. 28a ), sparsely branched, and usually brown-red in coloration. The largest specimen (the holotype) is 290 mm long and 200 mm wide. The branches are feather-shaped with shorter branchlets at the apex and towards the base. The branchlets are sturdy, departing perpendicular to the branch on all sides, in a bottlebrush arrangement. There are 3–5 branchlets per cm, they are usually a maximum of 30 mm long, shorter towards colony base, mostly simple with some secondary branching, and ramification usually occurs close to the branchlet base.

The polyps of the holotype are clavate and bulbous ( Fig. 28b,c ), sometimes with a flat adaxial surface (being compressed against neighbouring inner polyps; Fig. 28e ). The polyps are 2.5–2.8 mm high, placed at an almost right-angle to the branchlets at the branchlet base but upwardly inclined towards the branchlet tip (up to 45˚). They are spaced at 9–30 per cm at branchlet base and in a dense cluster at branchlet tip, where they form an almost solid cylinder of polyps (‘barrel-shaped’, Fig. 28c ) with 18–48 per cm. Each polyp has 8 longitudinal rows of scales, 8–15 scales in the abaxial rows (average 11, Fig. 28d ), and a reduced number adaxially. The scales are progressively wider and shorter from polyp head to base.

The operculum is flat. The operculars are arrowhead or lanceolate in shape ( Fig. 29a–f ) but can be wider and pentagonal, up to 420–510 µm high (average 460 µm), 230–410 µm wide (average 340 µm), with an average H:W of 1.4 (1.2–1.8). The inner opercular surface has a large, multi-keel ( Fig. 29a,f ) and many adjacent ridges resulting in a serrate distal edge whilst the proximal half is tuberculate. The outer scale surface has a deep longitudinal indentation ( Fig. 29b–e ), large granules extend into ridges that run perpendicular to the distal edge, and there can be tubercles along the proximal edge.

The marginals are wider than the operculars, 340–510 µm (average 440 µm), 380–470 µm high (average 430 µm), with an average H:W of 1 (range from 0.7–1.2). The marginals are elliptical in shape with a pointed distal edge ( Fig. 29g,h ). The inner surface has a small, simple keel with smaller adjacent keels leading to a serrated distal edge. The proximal two-thirds is tuberculate and distal third smooth lateral to the keel and ridges. The outer surface has a longitudinal groove with sparse, large granules occurring towards the proximal edge, where tubercles are also visible.

The submarginals are clearly visible from an anterior polyp view ( Fig. 28e ) as the distal edges curve slightly away from the polyp body. They are elliptical ( Fig. 29i–k ), wider than the marginals, 540–890 µm (average 700 µm), and about the same height, 350–550 µm (average 430 µm), with an average H:W of 0.6 (range from 0.4–0.9). The ridges are infrequent on the inner surface perpendicular to distal edge, the edge being serrate whilst the remainder of the inner surface is tuberculate. The outer surface has sparse granules proximally.

The body-wall scales are elliptical, very broad ( Fig. 29l–q ), curved around the polyp circumference, average height 380 µm (270–520 µm), width 790 µm (620–1000 µm), with an average H:W of 0.5 (range from 0.4–0.6). The inner surface is tuberculate with a narrow smooth band along the distal edge. The outer surface has large, sparse, peaked granules concentrated in the centre of the scale and sporadic tubercles proximally with the remainder being smooth whilst the distal edge has large serrations. All of the above sclerites of this species have a coarsely lobate proximal edge.

The coenenchymal scales are circular to elliptical ( Fig. 29r ), 240–320 µm diameter, with similar dimensions to the small body-wall scales, but flatter, with less curvature, and a strongly jagged distal edge.

Distribution

Thouarella parachilensis has been found 1000 km west of, and around, the waters of South Georgia Island and south to the Antarctic Peninsula , 90–480 m.

Remarks

The specimens of this species have long been incorrectly identified as Thouarella chilensis because of the densely clustered polyps at the branchlet tip that were mistaken for the densely arranged polyps found on that species, as described by Kükenthal (1908; 1915; 1924).

Comparisons

It is the cylindrical arrangement of the clustered, bulbous polyps at the branchlet tip that make T. parachilensis noticeably different from other Thouarella species , except for T. chilensis . Thouarella parachilensis has 8–15 abaxial body-wall scales per row (average of 11), a comparable number to T. koellikeri , T. chilensis , T. crenelata and T. brevispinosa .

The polyps of T. koellikeri have 7–10 scales in the abaxial rows and a tall operculum of large operculars with a simple keel. This is distinct from T. parachilensis , which has a flat operculum with much smaller operculars bearing a complex keel. Thouarella brevispinosa has 6–8 scales in the abaxial rows, which are distally flared, and colonies have more evenly spaced polyps than the clavate, clustered polyps of T. parachilensis ( Table 3).

The polyps of T. parachilensis are bulbous and more rounded, usually with a higher number of scales in the abaxial rows than those of T. crenelata or T. chilensis . The polyps of T. crenelata have a more open operculum in anterior view than those of T. parachilensis and polyps of T. chilensis are more stout and stocky in shape.

Species Group 2—polyps in pairs or whorls

Figures

FIGURE 28. Thouarella parachilensis sp. nov, holotype, USNM 98338: a) colony, 29 cm long, 20 cm wide; b,c) close up of ‘barrel-shaped’ clusters of polyps; d) abaxial polyp view; e) stereo opercular view. Photo by SJ.

FIGURE 29. Thouarella parachilensis sp. nov, holotype, USNM 98338: a,f) inner and b–e) outer surface of opercular sclerites; g) outer and h) inner surface of marginal scales; i,k) outer and j) inner surface of submarginal scales; l,n,p,q) outer and m,o) inner surface of body-wall scales; r) coenenchymal scales—top row right, middle row right, bottom row left show the outer surface, remainder inner surface.