Aethisis turriformis Xu, Lu & Xu 2024, sp. nov.

Aethisis turriformis Xu, Lu & Xu, sp. nov. urn:lsid:zoobank.org:act: A5BAFF87-FCEC-4B25-AA98-4AFE169D078B Figs. 3–4 Material examined. Holotype: RSIOOCT0241, station JL179 (13.3389°N, 134.5606°E), seamounts located on the south Kyushu Palau Ridge, 2104 m, 24 January 2021, DY60 cruise of R/V ShenHaiYiHao. Other material: MBM287341, voucher specimen isolated from the holotype. Diagnosis. With the characters of the genus. Description. Colony. Holotype in situ large, non-planar with a disc-shaped calcareous holdfast and branches dichotomously branched in different planes forming a tree-shaped colony (Fig. 3A). Holotype broken and incomplete after collection with the holdfast not recovered (Fig. 3B). Internodes up to 13 cm long, sometimes hollow. Nodes brown and short, concave inward. Terminal branchlets slender in situ, up to 55 cm (Fig. 3B). Coenenchyme thin and white after fixation (Fig. 3C). Polyps. Polyps turreted and cylindrical with an expanded distal part and an obvious constriction below the tentacular part, usually 3–6 mm in height and 2–5 mm in width (Fig. 3C–E). Polyps pink to orange after collection, and became white with brown color occurring on the distal part of the polyps after fixation. Polyps spaced widely on the branch, perpendicular to the axis or slightly tilted, arranged irregularly on all sides of the axis, up to 9 mm apart. Tentacular part conical or dome shaped with tentacles contractile and tightly folded on the distal part of polyps (Fig. 3C–E, G). Sclerites. Sclerites densely arranged in polyps and coenenchyme, covered with more or less shallow grooves (Fig. 3D, E). Rods in the back of tentacle rachis densely and longitudinally arranged, flat and often with two expanded and rounded ends, some of them with toothed lateral edges, occasionally branched or crossed, measuring 138–335 × 23–100 μm (length × width, the same below, Figs. 3D–G; 4D). Scales in pinnules longitudinally arranged, thick and usually with a slightly medial constriction and toothed edges, occasionally branched or crossed and covered with longitudinal ridges, measuring 54–112 × 20–62 μm (Fig. 4B). Sclerites absent and formed a bare, sclerite-free area at the base of each tentacle (Fig. 3D, E). Rods longitudinally arranged in the inter-tentacular area extending to the upper polyp body wall, often large and usually one or two in number, sometimes slightly projecting beyond the tentacles forming eight blunt points, measuring 948–1233 × 120– 138 μm (Figs. 3C–E, 4A). These rods were covered with ridge-like warts with the ends rough and granulated with deep grooves. Body wall with flat rods, sparse spindles and elongate thick scales (Fig. 4E, F) usually transversely or obliquely arranged, some of them longitudinally in the base of tentacular part, measuring 119–648 × 34–142 μm. They often have slightly toothed lateral edges, some are covered with warts or large ridge-like projections on the surface, occasionally branched or crossed. Scales have an obvious medial constriction and are more abundant at the basal body wall. Flat rods and thick scales in coenenchyme are similar to the polyp body wall but relatively small in length, arranged along the branches and occasionally sparse, measuring 96–213 × 40–98 μm (Figs. 3H, G). Rods in pharynx irregular and rough, covered with large blunt or conical projections on the lateral edge, occasionally partially crossed, measuring 73–100 × 25–43 μm (Fig. 4C). Type locality. Unnamed seamount located on the south Kyushu Palau Ridge, 2104 m. Etymology. The Latin adjective turriformis refers to the turreted polyps with an expanded and conical distal part of this species. Genetic data. MBM287341, 28S rDNA: PP992076, cox1: PP991396, mtMutS: PP999499. Distribution and habitat. Known only from the seamounts located on the south Kyushu Palau Ridge at water depth of 2104 m. Colonies grow on a rocky substrate (Fig. 3A). Remarks. Aethisis gen. nov. is the fourth genus in the clade J3. It is characterized by branches dichotomously branched in different planes, turreted polyps with a bare, sclerite-free area at the base of each tentacle, sclerites usually with toothed lateral edges, and flat rods and scales abundant in polyp body wall and coenenchyme. The new genus can be easily separated from Dokidisis and Explorisis because there are no scales in the polyp body wall and coenenchyme of the latter two genera (Lapointe & Watling 2022, Periasamy et al. 2023). Aethisis gen. nov. is similar to genus Jasonisis in sclerite forms, also including rods, needles and scales. However, the Jasonisis species have a planar colony and are covered by a thick tegument, have cylindrical polyps without a bare, sclerite-free area at the base of each tentacle, and the sclerites have more lobed edges, which are obviously different from Aethisis gen. nov. (Alderslade & McFadden 2012).