Thouarella porcupinensis Altuna & López-González 2019, sp. nov.

Thouarella porcupinensis sp. nov.

(Figs. 1 D–F, 7–9)

urn:lsid:zoobank.org:act: 2200E7BE-1384-4577-ADE8-12FA895B3C55

Material examined. Porcupine Bank, 14.09.2015, Stn. 32, 53.841°N– 13.378°W, 365 m, one broken colony (MNCN 2.04/2025, holotype).

Diagnosis. Colony pinnate, ramified in a plane, with isolated polyps. Polyps small, clavate, with 5–6 scales in the abaxial rows, 4–5 in the outer lateral rows, 3–4 in the inner lateral rows, and 2–3 adaxials. Marginal scales without apical projection, with at least those from abaxial rows having several perpendicular ridges on their inner side.

Description of the holotype. Colony broken lacking the holdfast and the distal end, 232 mm in height and 121 mm in width, slightly flexible, uniplanar, whitish to light cream in colour. Main stem almost round in cross-section, undulating in its lower part, 3.4 mm in diameter proximally, golden in colour, iridescent, with a faint longitudinal striation. Ramification pinnate, with up to five order branchlets. Up to 4–5 branchlets/cm given off alternatively left and right at 40–60°, every 1.8–2.9 mm along the main stem; branchlets separated 3.9–6.5 mm along each side of stem. Most of these branchlets developing into larger branches, with two up to 140 mm in length and 2.2 mm in basal diameter given off along one side of the stem, later curved upwards running almost parallel to it. One of the largest branchlets given off at 87 mm from proximal end, surpasses the broken distal end of main axis. Second order branchlets up to 1.5 mm in basal diameter given off regularly, with further higher order branchlets diminishing progressively in length and diameter; ultimate fifth order branchlets up to 12 mm in length and 0.4 mm in basal diameter. Smaller branchlets sometimes wavy, with their distal ends commonly curved.

Polyps abundant, 18–20/cm, arranged isolated all around branchlets and rather sparsely on main stem and axis of first order branches, more or less crowded, clavate, bent inward toward the axis, 1.05–1.30 mm tall (average 1.18 mm) and 0.48–0.65 mm wide (average 0.56 mm) distally, with greatest width at the circle of marginals. Body scales arranged in 8 longitudinal rows, with 5–6 in the abaxial rows, 4–5 in the outer lateral rows, 3–4 in the inner lateral rows, and 2–3 in the adaxial rows.

Operculum tall, conical, well developed, with 8 isosceles-triangle shaped opercular scales (Fig. 8A) in a single ring having a narrow flat to slightly rounded base and a pointed distal edge, sometimes double, up to 0.5 x 0.25 mm (H x W) (H: W of 1.84–2.57, average 2.27). Adaxial operculars tongue-like, smaller and narrower than the others, with a pronounced reduction of base width, up to 0.34 x 0.1 mm (H x W) (H: W of 3.16–3.63, average 3.41). Opercular scales flat to slightly incurved, with convex outer surface; a well-developed keel occurs on the inner side, seen as a deep furrow in the outer side. Outer surface with numerous more or less pointed granules extending radially from the proximal central area towards the distal end, where they may develop roughly into striations; inner surface with complex tubercles arranged in the same manner, developing into serrated striations distally.

Marginal scales mostly wider than high, up to 0.38 x 0.31 mm (H xW), or more or less quadrate, 0.27 x 0.28 mm (H x W), to slightly fan-shaped (Fig. 8B). Inner surface covered with complex tubercles tightly arranged extending radially from the proximal central area towards the distal end. Outer surface with complex tubercles and granules on the proximal end, that may develop roughly into pronounced striations distally. Distal end of abaxials and sometimes also of outer-laterals with several perpendicular ridges heavily pronounced on their inner side, giving a somehow castellated aspect to the edge, with more or less acute cusps separated by well-defined valleys (Figs. 7 A–C, 8B). Ridges may be finely serrated (Fig. 7C). Adaxial marginals smaller, up to 0.19 x 0.17 mm (H x W).

Body scales irregular (Fig. 8C), roughly rectangular (0.17 x 0.15 mm, H x W) to higher than wide (0.27 x 0.21 mm, H x W) or broader than high (0.24 x 0.28 mm, H x W), occasionally slightly fan-shaped with a more or less rounded proximal end (0.23 x 0.27 mm, H x W); most abaxials and eventually also distalmost outer-laterals with perpendicular ridges on their distal end, and similar inner and outer surfaces ornamentation as the marginals. Scales wider and larger towards polyp head. Adaxial scales 2–3, reduced in size, lacking ridges.

Coenenchymal scales arranged tightly in one layer, irregular to more or less circular to oval-shaped up to 0.30 mm in length, but usually smaller, around 0.11 x 0.15 mm. Outer surface granulate, forming connected ridges; inner surface covered with complex tubercles closely arranged (Fig. 9).

Etymology. The species name is derived from the geographical area, the Porcupine Bank, where the new taxon was discovered.

Remarks. The holotype is an incomplete colony lacking the proximal and the distal parts of its main stem. Given the thickness and wavy shape of the proximal end of the sample (Fig. 1E), it almost certainly corresponds to the basal main axis of the colony, and not to a branch of a bigger colony. Polyps are arranged isolated and occur also in the main stem although they are very scarce on it. Polyps are abundant but not evenly distributed in the branchlets. In the distal end of the largest first order branch, a few third order branchlets occur perpendicularly to the main plane.

Given its planar pinnate ramification with small isolated clavate polyps and its sclerome, with distinctive marginals and other body scales, the new species differs from other species of the genus and is hardly comparable with either. It clearly differs from Thouarella grasshoffi Cairns, 2006, the unique species in the genus accepted from the northeastern Atlantic (see Cairns 2006; Taylor et al. 2013). This species has colonies in bottlebrush growth, polyps in pairs or whorls and the marginals have an acutely pointed tip (Taylor et al. 2013). Northeastern Atlantic records of Thouarella hilgendorfi (Studer, 1878) (Thomson 1927; Grasshoff 1982) are based, according to Cairns (2006), on T. grasshoffi material. Furthermore, T. hilgendorfi is notably different from T. porcupinensis sp. nov. (see Taylor et al. 2013) and is of Indo-Pacific distribution. The species status of the material identified as Thouarella variabilis by Thomson (1927) and Tixier Durivault & d’Hondt (1975) from the Azores Archipelago is doubtful. Although this species was listed by Braga-Henriques et al. (2013), it is not included in the ERMS (Cordeiro et al. 2018b) as that species is considered of Circum-Antarctic distribution according to the recent generic revision of the genus Thouarella (Taylor et al. 2013), having important morphological differences anyway, at colonial and sclerome levels, to the new species here proposed.

According to Taylor et al. (2013), from the 25 valid species known worldwide, only T. bipinnata Cairns, 2006 from the Straits of Florida ramifies in a plane and has isolated polyps, but this species has a different colony morphology and sclerome (see Cairns 2006, fig. 1F, figs. 8–9). These authors recognized 17 species with isolated polyps worldwide, most of them having bottlebrush colonies. A few have bushy colonies with a bilateral appearance, and two, although being bottlebrush, have alternately pinnate (T. andeep Zapata-Guardiola & López González, 2010, SW Atlantic) to uniplanar appearance (T. crenelata Kükenthal, 1907, Circum-subAntarctic) which is not the case of T. porcupinensis sp. nov. Newly described T. taylorae Cairns, 2018 (in Cairns et al. 2018) from the North Pacific Ocean is essentially uniplanar but polyps may occur individually on the main branches and in pairs and whorls on the branchlets. Additionally, both the shape of the polyps and the body scales are different from T. porcupinensis sp. nov. (see Cairns et al. 2018).

One of the distinctive characteristics of the new species is the morphology of the marginal scales, particularly of their distal inner surface. These scales lack a pointed distal edge (spine), and instead have several perpendicular ridges heavily pronounced on their inner side, giving to the edge a somewhat castellated aspect (Fig. 7 A–C). This morphology is shared with other body scales of the abaxial rows, and the ridges certainly resemble those in the marginals and body scales of T. viridis Zapata-Guardiola & López-González, 2010 from Antarctica, an otherwise different species in colony structure (bottlebrush), morphology of the polyps and sclerome (see Zapata-Guardiola & López-González 2010a; Taylor et al. 2013).

The lack of a spine on the marginal scales and isolated polyps has been considered an attribute of the subgenus Epithouarella Kükenthal, 1915, which includes four species (T. crenelata, T. affinis Wright & Studer, 1889, T. chilensis Kükenthal, 1908, and T. viridis) (Cairns & Bayer 2009; Zapata-Guardiola & López-González 2010a). However, no subgeneric distinction was proposed by Taylor et al. (2013) in their review of the genus. These authors established two groups of species without taxonomic status (Group 1, isolated polyps; Group 2, paired or whorled polyps) by means of polyp placement, disregarding other characters considered in the past. We refer to their paper for an historical summary of the Thouarella species groups.

Most of the fragment ramifies in a plane, but the presence of two epizoic anemones up to 12 mm in diameter induces an anomalous growth, with the branches surrounding them becoming strongly curved and somehow distorted (Fig. 1F). Thouarella spp. were not cited as host for anemones in the review of Watling et al. (2011), but the Circum-Antarctic T. variabilis was reported by Taylor et al. (2013: fig. 2) as substrate for an unidentified anemone.

Distribution. At present, the species is only known from the Porcupine Bank, off Ireland, northeastern Atlantic, at 365 m depth.