Thouarella hilgendorfi ( Studer, 1878 )

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 : 76-77

18. Thouarella hilgendorfi ( Studer, 1878)

Plumarella hilgendorfi Studer, 1878: 648–649 , pl. 2, figs 15a–e

Thouarella hilgendorfi Wright & Studer 1889: 62 , figs 18–25; Versluys 1906: 24–29, pl. 2, fig. 7, text figs; Thomson & Henderson 1906:38 (list); Roule 1908: 1; Kinoshita 1908a: 21–22, pl. 5, fig. 42; Nutting 1912: 66–67; Aurivillius 1931: 248–252, pl. 5, fig. 8, text fig. 48; Chave & Malahoff 1998: Table 1 (listed)

Not Thouarella hilgendorfi Thomson 1927: 33–34 , pl. 1, fig. 23, pl. 4, fig. 4, 5; Carpine & Grasshoff 1985: 32 (= T. grasshoffi )

Thouarella typica Kinoshita, 1907: 230 ; 1908a: 23–24, pl. 2, fig. 9, pl. 5, fig. 43; Nutting 1912: 68

Thouarella hilgendorfi forma plumatilis Aurivillius, 1931: 252–256, pl. 5, fig. 9

Thouarella (Euthouarella) hilgendorfi Kükenthal 1915: 150 ; 1919: 415–416; Cairns 2006: 188 (discussion); Cairns & Bayer 2009: 28, figs 6m –s (listed); Cairns 2010: 415–422

Thouarella sp. cf. T. typica Grigg & Bayer 1976: 171 (listed); Parrish & Baco 2007: 192 (listed)

Material examined: Holotype, ZMB Cni 2070 (see Versluys, 1906). “Jeddobay” (= Tokyo Bay), Japan, 548 m, 60 mm fragment.

Other material: USNM 56812, Star II (station unknown), Kaiwi Channel between Oahu and Molokai, 21°18’N, 157°32’W, 366 m, 1977, 1 large dried colony, SEM C1393-1397.

Description

Modified from description in Cairns (2010):

The colonies are flabellate, consisting of several main branches that are irregularly dichotomous. Each main branch is covered by numerous closely spaced, undivided, 20–25 mm length branchlets originating from all sides of the main branches in a bottlebrush arrangement. The largest specimen ( USNM 56812) is 48 cm tall, 34 cm wide, with a broken basal stem, the diameter of which is 9.5 mm. The axis of the holotype is pale yellow to bronze in colour, and covered by white coenenchyme and polyps.

The polyps of the holotype are 1–1.4 mm high, flared distally, slightly inclined upward, in whorls of 3 on branchlets and placed randomly on larger-diameter branches, with 6–7 whorls per cm. Approximately 1 in 20 polyps are highly modified by a pair of parasitic copepods, with each modified polyp being much larger, up to 1.6 mm high and 1.2 mm in diameter and thus 2–3 times the volume of a typical polyp. The parasite-modified polyps lack operculars, and their body-wall scales flare outward, having a ridged inner face, and a coarsely serrate distal margin. Generally the polyps have 8 longitudinal rows of body-wall scales, usually 6 or 7 abaxial pairs, 5 or 6 outer-lateral pairs, 3 or 4 inner-lateral pairs, and only 1 or 2 adaxial pairs.

The operculars are triangular, often arranged in 2 quartets, alternating in size, with the larger operculars reaching 350–450 µm high (H:W of 1.4–2.1) but the smaller operculars only reaching 180–230 µm high (H:W of 1.6–2.2) and are highly curved. The opercular outer surface is smooth with a serrate distal edge. The longitudinally concave outer surface corresponds to the smooth, convex (not ridged or keeled) inner surface.

The marginals also occur in 2 quartets, as do submarginals, the innermost 4 aligned with inner marginals, and outer 4 submarginals with outer marginals. The marginal scales have a broad elliptical base, a prominently spinose distal projection, and are up to 500–600 µm high and 300–400 µm wide (H:W of 1.2–1.8). The distal 60–65% of the scale is occupied by a projecting spine. The outer distal surface is smooth and the proximal area is covered with granules. The inner surface bears 3–4 prominent spines, and finely serrate ridges that form a complex keel that fits into the longitudinal furrow on the corresponding opercular outer surface.

The submarginal scales are similar to the marginals but with a much shorter distal spine (35% length of scale) and a correspondingly lower H:W of 1.2 with a small simple keel on their inner surface. The body-wall scales are crescent-shaped with a finely serrate distal edge, a smooth outer surface, and are usually wider than high (H:W of 0.6–0.8). The adaxial side of the polyps are covered with particularly wide adaxial and inner lateral body-wall scales.

The coenenchymal scales are similar to body-wall scales, mostly elliptical in shape with a smooth, flat outer surface, approximately 250 µm wide and 150 µm high, and a finely serrate distal edge.

For images see Cairns (2010).

Distribution

Hawaii , Japan, Indonesia, and Indian Ocean at depths from 164–750 m.

Remarks

Thouarella typica is identical to T. hilgendorfi and were synonymised in Cairns (2010).

Comparisons

Within Group 2 only three species have a bottlebrush branching arrangement: T. grasshoffi Cairns, 2006 , T. hilgendorfi , and T. laxa . Thouarella grasshoffi and T. hilgendorfi have true bottlebrush branching arrangements whereas branchlets of T. laxa are found mostly in one plane, although the length and flexibility of branchlets means the latter can appear bottlebrush. The colonies of T. grasshoffi tend to be taller than they are wide, with rare branching, whereas colonies of T. hilgendorfi are wider than tall, and flabellate. The polyps of T. grasshoffi and T. hilgendorfi have a very similar size, those of the former being pointed and conical, with slightly shorter marginals, compared with the distally flared polyps of the latter.