Thouarella parva 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 : 89-90

23. Thouarella parva Kinoshita, 1908

Fig. 40 a,b

Thouarella (Diplocalyptra) parva Kinoshita, 1908d: 53–56 , figs 1–3; Cairns & Bayer 2009: 28 (list)

Thouarella (Amphilaphis) parva Kükenthal 1915: 149 (key); 1919: 410; 1924: 290 (key)

Material unavailable: Holotype, Kodzu Island, Japan, depth unknown. Unfortunately the holotype was not present within the University of Tokyo Museum collection (Dr Ueshima, pers. comm.), and so Kinoshita’s original description of a 73 mm fragment (1908d) is summarised below.

Description

The colony is uniplanar with dichotomous branching. The branchlets diverge from the main stem at around 50˚, 5–13 mm between branchlets. The colony colour is white to light yellow.

The polyps are 1 mm high and upwardly inclined to the branchlets at around 45˚, the widest point being around the marginals. They are slender toward the base ( Fig. 40a ), arranged in pairs, with a density of about 6 per cm, and each has 8 longitudinal rows of body-wall scales. There are 5–6 scales in the abaxial rows, and 5 in the outer and inner lateral rows, reducing to 4 adaxially.

From a lateral view the operculars are completely concealed by the marginals. Very small accessory operculars are present ( Fig. 40 bI). The operculars are lanceolate ( Fig. 40 bII), 160–360 µm high and 90–160 µm wide. The distal half of the outer opercular surface is slightly concave and both the inner and outer surfaces have granules arranged radially in the proximal area. The inner surface is likely to be tuberculate proximally, as is typical for the genus.

The marginals are an irregular triangle-shape ( Fig. 40 bIII) and approximately the same size as the largest opercular (400 µm), although wider proximally.

The body-wall scales are not as tall as the marginals (350–380 µm) and are broader ( Fig. 40 bV, bVI). The outer surface of the body-wall scales has radially arranged granules from the central proximal area whilst the inner scale surface is tuberculate with a smooth band along the distal edge, occasionally with several ridges perpendicular to the distal edge.

The coenenchymal scales are smaller than body-wall scales, and circular to elliptical in shape. The outer surface is sculpted and folded with sparse tubercles on the inner surface. The distal and lateral edges of all sclerites are finely serrate with a coarsely lobate proximal edge.

Distribution

This species is only known from Kodzu Island and Sagami Bay, Japan. The depth from which the sample was taken is unknown.

Remarks

Kinoshita was the first to note accessory operculars in Thouarella (1908d, Fig. 2 , shown here in Fig. 40b ) and T. parva remains one of the few Thouarella species with this kind of sclerite.

The marginals of the polyps of T. parva ( Fig. 40 bIII) appear to have a small keel on their inner surface, and the specimen is thus considered to be Thouarella . However, this is far from clear and the rounded distal edge of what appear to be marginals in Fig. 40b , and lack of a clear keel could indicate that this is actually a species of Plumarella . More material is required to confirm the placement of T. parva within Thouarella .

Comparisons

Dichotomous branching precludes this species from being T. hilgendorfi , T. moseleyi , T. laxa , T. tydemani , or T. grasshoffi from within Group 2. Additionally, these species all have tall, triangular marginals that are absent in T. parva .

Only two other Thouarella species have dichotomous branching: T. coronata and T. biserialis . The polyps of T. coronata diverge at 90˚ to the branch, whereas those of T. parva depart at 45˚. This seems to be a very small difference, however, without more material of T. parva it is impossible to determine the extent of the character differences between these species. There are believed to be specimens of T. parva in Japan (Cairns, pers. comm.), but until this material is examined these species are considered to be distinct.

Polyps of both T. parva and T. biserialis depart from branchlets at approximately 45˚ and all their sclerites appear to be very similar shapes and sizes. The polyps of T. biserialis have marginals with a distinct keel, which may be present on T. parva , but the polyps of T. biserialis are clavate whereas those of T. parva are modestly flared with a relatively tall operculum.

Figures

FIGURE 2. Animals found within the branchlets of Thouarella specimens: a) Polychaete found along stem of the holotype of T. affinis; b) crinoid arboreal cup in branchlets of T. crenelata (ZSL AE57); c) anemone attached to branchlet of specimen of T. variabilis (SMF, MD42, sta. 22).

FIGURE 40. Thouarella parva, holotype: a) lateral polyp view, modified from Fig. 1 Kinoshita, 1908d; b) sclerites from Kinoshita, 1908d—I. accessory operculars, II. operculars, III. marginals, IV. submarginals, V,VI. body-wall scales. Thouarella andeep, USNM 1123418: c,d) inner surface of marginal scales.