Thouarella tydemani 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 : 85

21. Thouarella tydemani Versluys, 1906

Thouarella tydemani Versluys, 1906: 34–35 , pl. 1, fig. 2, figs 34–37 (in text)

Thouarella tydemany Brito 1993: 220–221

? Hookerella pulchella Gray, 1870: 45

Thouarella (Euthouarella) tydemani Cairns & Bayer 2009: 28 (listed)

Material unavailable: Holotype, COEL09256, ZMA, Siboga expedition, sta. 297, Lesser Sunda Islands, Indonesia, 10˚39’S, 123˚40’E, 520 m, 27 Jan 1900, 200 mm colony. Only 3 mounted slides remain of this species, images of which were seen. They contain 2 branchlets, polyps and coenenchymal scales. The original colony is presumed lost as the holotype was not present at ZMA ( Zapata-Guardiola & López-González 2010a) or any of the other museums contacted within this study. As no material was available the type description was used for species comparisons.

Description

The colony is flat with infrequent uniplanar branching. The branchlets are simple, 15–20 mm long, rarely 30 mm, alternately pinnate with a few ventral branchlets.

The polyps are distally flared, approximately 1.5 mm high, standing at 80–90˚ inclination from branchlets, paired, rarely in whorls, 3–6 per cm with some polyps on the main branch.

The operculars are in a modest cone of 4 larger, outer, longitudinally concave operculars and 4 smaller, inner, distally blunt operculars. The marginals are 450–500 µm high, almost spinose with a keel visible on the inner surface. Body-wall scales appear circular, some bearing ridges perpendicular to the distal edge.

Recently published additional description and images are in Zapata-Guardiola and López-González (2010a).

Distribution

Known only from the type location off the Lesser Sunda Islands, Indonesia, at 520 m depth .

Remarks

Versluys (1906) separated Thouarella laxa and T. tydemani , the latter having wider and larger polyps. Zapata- Guardiola and López-González (2010a) illustrated that the variation in nearly all characters (size of polyps, number of whorls per cm, number of polyps per whorl etc) in T. laxa was broad enough to encompass the dimensions seen in T. tydemani . The only difference found between T. laxa and T. tydemani was that the body-wall scales of the latter have short ridges perpendicular to the distal edge, which are absent in T. laxa .

Versluys (1906) also considered Hookerella pulchella Gray, 1870 very similar to T. tydemani in colony form but he did not mention the number of polyps per cm or the sclerite shape. Without a reliable illustration or accurate description from Gray (1870), Versluys described T. tydemani , ignoring H. pulchella (the holotype or a specimen of which cannot be located).

Comparisons

Thouarella tydemani was compared to T. laxa by Versluys (1906) and rightly so as the polyps of these species are nearly identical in every respect. Body-wall scales of T. tydemani may bend away from the polyp body, have ridges perpendicular to their distal edge, and have slightly shorter marginals than are found on T. laxa (this is in contrast to Zapata-Guardiola & López-González, 2010a, who found polyps of T. laxa had marginals that were on average 370 µm and thus shorter than those of T. tydemani ). However it is the branching pattern that makes these species truly distinct. Colonies of T. laxa have long, flexible branchlets, departing the stem in at least 3 directions, whereas colonies of T. tydemani are mostly pinnate with more rigid branchlets. Additionally, the polyps of T. laxa have a flat operculum and branchlets inclined at a 45–60˚, rather than 90˚ as in T. tydemani . More material of T. tydemani would help to assess further differences between these two species.

Polyps of T. tydemani are distally flared and look very similar to those of T. hilgendorfi . However, the pinnate branching structure of T. tydemani differentiates this species from the bottlebrush branches of T. hilgendorfi .