Thouarella (Thouarella) debilis, Cairns & Häussermann, 2021

Cairns, Stephen D. & Häussermann, Verena, 2021, A new species of Thouarella from Chilean Patagonia, Spixiana 44 (1), pp. 1-8 : 4-7

Thouarella (Thouarella) debilis sp. nov.

Figs 1-4

Thouarella (Thouarella) sp. 2 Ofwegen, Breedy & Cairns, 2008: 209-210, 955 (including 5 figures, one in situ).

Types. Holotype: Lenca , Chile, 32 m, colony and SEM stubs 1223, 1226, 2565-2566, USNM 1116614 . – Paratypes: Lenca, Chile, 28 m, 8 Feb 2014, HF19-5, Museo Nacional de Historia, Santiago, Chile, MNHNCL CNID-15059 ; Lenca , Chile, depth unknown, 24 March 2001, USNM 1569221 ; Lenca , Chile, 33 m, 8 Feb 2014, HF19-5, ZSM 20190632 .

Type locality. Lenca (41°38.298'S, 72°40.164'W), Chile, 32 m.

Distribution. Lenca is the only site out of hundreds of dive sites throughout Chilean Patagonia where this species was found.

Description

Colonies are very sparsely branched, the main stem sometimes remaining simple, in other colonies producing one or two secondary stems ( Fig. 2A, B ). The holotype is 33 cm in height and has a simple unbranched stem, whereas the largest of specimens is up to 53 cm in height. Branchlets diverge from the main stem in all directions ( Fig. 3A ) but are most common on opposites of the stem, producing a loose bottlebrush arrangement tending toward pinnate. The base of the main may be up to 2 mm in diameter, whereas the branchlets are very thin, filiform, only 0.5- 0.15 mm in diameter and up to 50 mm in length, producing a weak or flaccid support for the polyps. The branchlets are themselves unbranched. The stem is pale yellow in colour, the polyps are white. The polyps are flared in shape ( Fig. 3C, E ), 1.2-1.7 mm in length, and 12-16 of them occurring randomly (not paired or in whorls, Fig. 3A ) on a 1 cm length of branchlet.

The body wall scales are arranged in eight longitudinal rows, the number of scales in each row decreasing in number (but not size) from ab- to adaxial polyp side. The body wall sclerite formula is: 7-9: 5-9: 3-5: 2-3, the abaxial scales ( Figs 3C , 4F ) increasing in size toward the base of the polyp. The marginal scales ( Figs 3F , 4A- B ) are diamond shaped, with broad lateral wings and thus a low L: W ratio of 1.1-1.6. They measure 0.45-0.65 mm in length, including an elongate distal spine; their distal inner surface bears a prominent, sometimes multi-ridged, serrate keel ( Fig. 4B ); their outer surface is sparsely granular proximally and smooth distally. Sometimes the submarginal scales ( Fig. 4C ) have a shorter pointed distal spine (length of scale about 0.55, L:W =0.9-0.95), others having a rounded distal edge consistent with the other body wall scales. The body wall scales ( Fig. 4F ) are fan-shaped, usually broader than tall (L:W =0.6-1.0), 0.35-0.45 mm in height, and have a straight, finely serrate distal edge. The opercular scales ( Fig. 4D- E ) are lanceolate in shape, 0.45-0.52 mm in length, having a L: W ranging from 1.4-2.0. Like the marginals, they bear a prominent serrate inner keel ( Fig. 4E ) and a sparsely granular outer surface. The operculum itself is relatively low. The coenenchymal scales ( Fig. 4G- H ) are circular to elliptical in shape, thin, and imbricate, ranging from 0.15-0.40 mm in greater diameter. Their upper surface bears prominent ridges that radiate from a boss near the base of each scale.

The colonies were all whitish in colour, attached to moderately steep rocky substrata covered with some sediment, with the colony protruding perpendicular from the rock.

Associated species. The hard substratum below 15 m is densely populated with the primnoid gorgonian Primnoella chilensis ; below approximately 20 m numerous deep-water sea anemones such as Actinostola chilensis McMurrich, 1904 have been recorded. At vertical or overhanging sites, the scleractinian coral Desmophyllum dianthus (Esper 1794) is found. The hard substratum around the gorgonians is inhabited by numerous holothuriids of the species Psolidium disciformis (Théel 1886) , the zoanthid Epizoanthus fiordicus Sinniger & Häussermann 2009 , the bryozoan Cellaria malvinensis (Busk 1852) , the sea anemone Gonactinia prolifera (Sars 1835) and numerous species of sponges. The crinoid species Astrotoma agassizii Lyman, 1875 , the octocoral Clavularia magelhaenica Studer, 1878 , and the gastropod Nasserius gayii (Kiener 1834) have been recorded using Thouarella debilis as substrate.

Comparisons. When run through the comprehensive key to all Thouarella species that have isolated polyps, i. e., the nominate subgenus (Taylor et al. 2013), T. debilis comes closest to T. chilensis Kükenthal, 1908 , another species obviously also known from Chile. However, T. chilensis differs in having a robust bottlebrush shape, much shorter (15 mm length) and thicker (0.25 mm diameter) branchlets, accessory opercular scales, and larger (2.5-2.7 mm) polyps.

Remarks. This species was briefly described and illustrated by Ofwegen et al. (2009) but not named, except for the common name of “limp bottlebrush gorgonian”, as only one specimen was available. Since then more specimens have been collected and thus a formal description is given herein. It is one of the shallowest of the 34 species in the genus.

Distribution. Known only from Lenca (about 41.61° S, 72.66° W), Los Lagos Region, Gulfo de Ancud, Chile ( Fig. 1 ), 28- 38 m.

Etymology. Named debilis (Latin for weak), in allusion to the weak, limp, or flaccid colony strength.

Figures

Fig. 1. Type locality of Thouarella debilis sp. nov. in shallow water of the Chilean fjord region. Triangle: study sites where T. debilis was collected. Squares: study sites where T. debilis was not found.

Fig. 2. Thouarella debilis sp. nov. in situ. Lenca, 28-35 m. A. Several specimens of T. debilis surrounded by numerous sea cucumbers of the species Psolidium disciformis (white). Next to the specimens the sea urchin Arbacia dufresnii (Blainville, 1825) and the brachiopod Magellania venosa (Solander, 1789). Photo: Ulrich Pörschmann; B. Specimen of T. debilis with epifauna: the crinoid Astrotoma agassizii and the octocoral Clavularia.

Fig. 3. Holotype of Thouarella debilis sp. nov., polyps and sclerite. A. Distal branchlet showing several polyps (stereo view); B. oblique adaxial view of a polyp; C. abaxial view of a polyp; D. lateral view of a polyp; E. lateral view of a polyp (stereo pair); F. marginal scale. All scale bar measurements in mm.

Fig. 4. Holotype of Thouarella debilis sp. nov., sclerites. A. Marginal scales; B. keel on inner distal face of a marginal scale; C. submarginal scales; D. opercular scales; E. keel of inner distal face of opercular scale; F. body wall scales; G. coenenchymal scales; H. coenenchymal scales in situ. All scale bar measurements in mm.