Thouarella coronata Kinoshita, 1908

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 : 86-89

22. Thouarella coronata Kinoshita, 1908

Figs 34 , 35

Thouarella (Diplocalyptra) coronata Kinoshita, 1908c: 519–520 , fig. 2; 1908b: 56–59, figs 4–6 (in text); Cairns & Bayer 2009: 28 (list), 35, figs 7a–g

Thouarella coronata Aurivillius 1931: 255 (listed)

Thouarella (Euthouarella) coronata Kükenthal 1915: 150 (key); 1924: 296 (key)

Material examined: USNM 50118, fragment of holotype, UMUT, Uji Island , Kyushu Island, 146 m, May 1908, 13 cm colony of which we viewed 20 mm. A small fragment of the holotype was available for study, however, the colony shape and branchlet arrangement narrative below relies heavily on the original description .

Description

The colony is mostly sympodially branched with dichotomous branching in one upper portion of the colony (top left of Fig. 34a ). Basal branchlets are up to 50 mm long, 5–12 mm apart, and on rare occasions 20 mm apart. The axis is brown with a yellowish metallic lustre.

The polyps are distally flared with a slender polyp body ( Fig. 34d,e ) 1.9–2.1 mm high, standing perpendicular to the branchlet in pairs and sometimes whorls of 3 ( Fig. 34c ), with 5–7 pairs or whorls per cm. There are 8 marginals, but only 7 longitudinal rows of body-wall scales with 5–6 scales in the abaxial rows.

The operculars are lanceolate to triangular in shape ( Fig. 35d–h ), 260–455 µm high (average 290 µm), 120–240 µm wide (average 180 µm), with an average H:W of 1.6 (range from 1.3–2). The outer surface is smooth whilst the inner surface has a small elliptical tuberclulate area proximally and a smooth distal area.

Beneath the operculars are 3–4 (perhaps more in other samples) small accessory operculars ( Fig. 35a–c ) which are irregular or tear-shaped, 80–200 µm high (average 150 µm), 70–140 µm wide (average 100 µm), with an average H:W of 1.1. The outer surface is smooth, the inner surface is also smooth with a small patch of tubercles proximally. The scale edges are relatively smooth (not serrated).

The marginals are equilateral triangle-shaped with a rounded proximal edge ( Fig. 35i–k ), 430–560 µm high (average 490 µm), 270–330 µm wide (average 310 µm), with an average H:W of 1.6 (range from 1.3–2.1). The outer scale surface is smooth distally with granules proximally. The inner surface has a multi-channelled keel with smooth areas lateral to the keel and tubercles covering the proximal half below the keel base. A marginal scale’s proximal edge is roughly lobate, and may be angular.

Some submarginals have small keels or ridges on the distal edge of the inner surface and are a wide tear-shape and pointed distally ( Fig. 35l,m ). They have a tuberculate inner surface with a narrow smooth band along the distal edge whilst the outer surface is smooth with some granules proximally.

Body-wall scales are circular ( Fig. 35n–p ), 190–340 µm high (average 250 µm), 200–310 µm wide (average 240 µm), with an average H:W of 1.1 (range from 0.9–1.2). The outer surface is smooth, sometimes with granules proximally whilst the inner surface is tuberculate with a smooth band along the distal edge and infrequent small ridges running perpendicular to the edge. The distal edge of all polyp sclerites of this species is finely serrate (unless otherwise stated) whilst the proximal edge is coarsely lobate.

The coenenchymal scales are circular ( Fig. 35q ), around 130 µm diameter and much smaller than the bodywall scales. The outer scale surface is smooth and slightly concave with edges raised from the axis whilst the inner surface is tuberculate.

Several hundred cylindrical rodlets were found in each tentacle.

Distribution

Known only from type locality, Kyushu Island , Japan, 146 m depth .

Remarks

This is the only Thouarella species known to contain tentacular rodlets, a form of sclerite often found in Plumarella . It is also the only Thouarella species known to have a sympodial branching pattern.

Comparisons

Although the majority of the T. coronata colony is sympodially branched a portion is dichotomously branched (more examples of this species are required to confirm the branching pattern). Apart from T. coronata , only two other species within Group 2 have dichotomous, uniplanar branching: T. parva , also from Japan, and T. biserialis ( Nutting, 1908) , from Hawai’i. Kinoshita’s drawings (1908d, figs 1, 2) indicate that T. parva differs from T. coronata in having shorter, more rounded marginals and polyps diverging from branchlets at approximately 45˚ rather than 90˚.

The sclerites of polyps of T. biserialis and T. coronata are very similar. The marginals of polyps of T. biserialis appear to curve over the operculum creating a cylindrical, rounded polyp, whereas those of T. coronata are flared outward. The polyps of the former are inclined at 45˚ and of the latter are perpendicular to branchlets. The importance of these characters remains unclear, so for now these species are considered to be distinct.

Figures

FIGURE 34. Thouarella coronata, holotype, UMUT: a) 13 cm colony; b) close up of polyps; c) whorl of three polyps; d) abaxial polyp view; e) lateral polyp view; f) stereo opercular view. SEM by RZG.

FIGURE 35. Thouarella coronata, holotype, UMUT: a,b) outer and c) inner surface of accessory operculars; d,g,h) outer and e,f) inner surface of opercular scales; i,j) outer and k) inner surface of marginal scales; l,m) inner surface of submarginal scales; n) inner and o,p) outer surface of body-wall scales; q) coenenchymal scales—inner surface top row left, bottom row right and middle; remainder are the outer surface. Some SEM by ZGR.