Thouarella laxa Versluys, 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 : 81-84

20. Thouarella laxa Versluys, 1906

Figs 32 , 33

Thouarella laxa Versluys, 1906: 30–32 , pl. 1, fig. 5; pl. 3, fig. 8; text figs 28–33; Aurivillius 1931: 255–256

Not Thouarella laxa Kükenthal & Grozawsky 1908: 36–37 , pl. 2, fig. 13

Thouarella (Euthouarella) laxa Kükenthal 1915: 150 ; 1919: 417; 1924: 293–294, text fig. 164; Cairns & Bayer 2009: 28 (in list) 4; Zapata-Guardiola and López-González 2010a: 72–78

Thouarella flabellata Kükenthal, 1907: 207

Thouarella (Euthouarella) flabellata Kükenthal 1915: 150 (key); 1919: 408 (key), 418–420, pl. 42, fig. 64, figs 182–186 in text; 1924: 294–295; Cairns & Bayer 2009: 28 (listed)

Thouarella regularis Kükenthal, 1907: 206–207

Thouarella tenuisquamis Kükenthal, 1908: 11 ; 1915: 150 (key), 151

Thouarella (Euthouarella) tenuisquamis Kükenthal 1919: 408 (key), 421, pl. 42, fig. 65, figs 187–190 (in text); 1924: 295; Cairns & Bayer 2009: 28 (listed)

Thouarella carinata Kükenthal, 1908: 11–12 ; 1915: 150 (key)

Thouarella (Euthouarella) carinata Kükenthal 1915: 150 (key); 1919: 408 (key), 423–425, pl. 42, fig. 66; 1924: 296; Cairns & Bayer 2009: 28 (listed)

Material examined: Holotype of T. laxa, ZMA, COEL 03576, Siboga expedition, sta. 88, Strait of Makassar, Sulawesi, Indonesia, 0˚34”06’N, 119˚08’05”E, 1301 m, 20 June 1899, 2 branchlets (80 mm, 90 mm); Holotype of Thouarella flabellata , sta. 257, east coast of Somalia, 1˚48’02”N, 45˚42’05”E, 1644 m, 3 fragments of 75 mm, 45 mm and 40 mm; Syntype of Thouarella tenuisquamis, MNHWU , northwest of Sumatra, Malaysia, south of Nicobar, 4˚53’01”N, 93˚33’05”E, 752 m; Syntype of Thouarella carinata, USNM 50127, Golden Hind, sta. 38, Okinawa and “Urugakanal”, Japan, 731 m, 85 mm fragment.

Description

The colonies are sparsely branched ( Fig. 32a ). The branches generally have alternate pinnate branchlets with infrequent branching between these 2 planes and sometimes on the dorsal face. This forms a rudimentary bottlebrush arrangement ( Fig. 32b ) that can form a feather-shape. Branchlets are flexible, upwardly inclined at 45˚, generally simple, with the longest being approximately 40 mm.

Polyps of the holotype are rarely on the main stem, usually in pairs or whorls of 3 on branchlets, with a density of 5–7 pairs per cm, distally flared ( Fig. 32c,d ), upwardly inclined at 45–60˚, and 1.2–1.5 mm high. Each polyp has 7 longitudinal rows, 5–6 scales in each abaxial row.

The operculars are arranged in roughly 2 alternate rings of 4 ( Fig. 32e ). In the inner ring the scales are smaller ( Fig. 33a–c ), 280–300 µm high (average 292 µm), 140–210 µm wide (average 166 µm), with a H:W of 1.8 (range from 1.4–2.1). In the outer ring the scales are larger 370–630 µm high (average 500 µm), 120–370 µm wide (average 292 µm), with a H:W of 1.9 (ranges from 1.3–3.1). The larger operculars are triangular ( Fig. 33e ) although, if broken, they have a rounded, blunt apex, usually tapering slightly to a narrow distal edge ( Fig. 33f ), making them tongue-shaped. The outer opercular surface is smooth and concave longitudinally, having small granules proximally and tubercles at the base. The inner surface has fine tubercles covering the proximal third to half of the scale, the remainder is smooth with longitudinal central ridges (no distinct keel). The smaller operculars are lanceolate with a smooth outer surface that has a small number of granules at the base and is slightly concave; the inner surface is smooth with fine tubercles over the proximal quarter to third.

The marginals are 570–800 µm high (average 705 µm), 370–550 µm broad (wider than largest opercular), with an average H:W of 1.5 (range from 1.3–1.7). They have a circular to diamond-shaped base and a triangular, acutely pointed distal edge ( Fig. 33f–h ). The outer surface is smooth with low relief granules proximally whilst the inner surface has 2 or 3 ridges longitudinally placed along the keel (which is sometimes flattened) and tubercles covering the proximal half in a semi-circle leaving smooth wings lateral to the keel and along the distal edge.

The submarginals are as described below for body-wall scales but slightly wider, 410–490 µm (average 470 µm), and taller, 500–610 µm (average 570 µm), with a H:W of 1.2. They have a pointed distal edge and a small keel on the inner surface ( Fig. 33i,j ), which has adjacent ridges perpendicular to the distal edge.

The body-wall scales are usually circular ( Fig. 33k–n ), 250–590 µm high (average 320 µm), 280–390 µm wide (average 310 µm), with an average H:W of 1 (range from 0.6–1.7). The outer surface is mostly smooth with some granules proximally whilst the inner surface is tuberculate with a smooth band along the distal edge.

The coenenchymal scales are circular to elliptical ( Fig. 33o ), 100–310 µm high (average 200 µm), 130–290 µm wide (average 200 µm), with a H:W of 0.4–1.5 (average 1). All the sclerites of this species have a finely serrate distal edge and roughly lobate proximal edge.

Distribution

This species occurs from the east coast of Africa ( Somalia) to eastern Asia (Sumatra, Philippines, Japan) at depths of 400–1644 m.

Remarks

Thouarella laxa was recently redescribed by Zapata-Guardiola and López-González (2010a). However, the polyp illustrated was incongruent with the holotype in that it showed the polyp head turning at an angle rather than a regular distally flared shape ( Fig. 32c,d ).

Although T. laxa , T. carinata , T. flabellata , and T. tenuisquamis have been described from disparate locations such as Somalia and Japan, at a polyp and sclerite level these specimens are identical. Thouarella flabellata has fewer pairs/whorls of polyps per cm (5–6) than T. tenuisquamis (7–8), T. laxa (5–7), and T. carinata (7–8). Thouarella carinata is more likely to have 3 polyps in a whorl whereas the remaining species tend towards pairs. However, the number of polyps per whorl may increase with colony age and is variable in other Thouarella species (e.g. T. grasshoffi ), so this small discrepancy should not be considered in defining species. The T. carinata and T. tenuisquamis holotypes are single branches and may even be one branch of a flabellate colony (see Fig. 32a,b of T. laxa ). Thouarella carinata also has a more extended distal edge on its marginals, and the holotypes of the remaining species are in a relatively poor condition with few intact polyps, many having marginals reduced in length through wear. However, the marginals that were intact looked identical to those of T. laxa . In all these specimens the inner surface of the small operculars tended to be smooth and larger operculars had a longitudinally ridged area distally. The outer surface of all sclerites is smooth with sparsely placed granules. The differences described above are minor and despite the long distances between type localities, the minor differences in branching, polyp and sclerite shapes are not sufficient to delineate unique species. Therefore, T. carinata , T. flabellata , and T. tenuisquamis are thus proposed for synonymisation with T. laxa , this name having priority.

Comparisons

Polyps of T. laxa have a similar distal flare as those of T. hilgendorfi and T. tydemani and the sclerites of these species are all nearly identical in shape. Colonies of T. laxa however have long, flexible branchlets emanating from the stem in at least three directions whilst branching on T. tydemani is alternately pinnate. The branchlets of T. hilgendorfi are bottlebrush but branching is denser, with sturdier, less flexible branchlets, and there are more whorls and pairs per cm than found on T. laxa . These characters could be affected by environmental factors and, at a polyp level, these species are similar. Sampling of fresh material from type locations and perhaps genetic studies could shed light on the relationship between these two species and T. grasshoffi , which also has a similar polyp structure.

The polyps of T. moseleyi are more rounded than those of T. laxa and consequently the former have shorter, narrower marginals. Additionally, the operculars of the former make a better-formed cone than those in the polyps of the latter and there are several ridges running perpendicular to the distal edge of the submarginals, a character not present in the polyps of T. laxa . Only a minute piece of T. moseleyi was examined, so more material is required to confirm the difference between these species as sclerite measurements, sclerite arrangement, and polyp arrangement are very similar.

Figures

FIGURE 32. Thouarella laxa, holotype, ZMA COEL03576: a–c,e) original images of holotype from Versluys, 1906, a) 20 cm colony; b) close up of small branch; c) pair of polyps; e) stereo opercular view of polyps. Thouarella carinata (now synonymised with T. laxa), syntype, USNM 50127: d) polyp.

FIGURE 33. Thouarella laxa, holotype, ZMA COEL03576: a,b,d) inner and c,e) outer surface of opercular scales; f) outer and g,h) inner surface of marginal scales; i,j) inner surface of submarginal scales; k,n) inner and l,m) outer surface of body-wall scales; o) coenenchymal scales—outer surface bottom right, remainder are the inner surface.