Dentatisis projecta Xu, Lu & Xu 2024, sp. nov.

Dentatisis projecta Xu, Lu & Xu, sp. nov. urn:lsid:zoobank.org:act: D5F162A9-CAFE-4988-9C03-49CB34C3CE7B Figs. 13–15 Material examined. Holotype: RSIOOC0210, station JL171 (16.9422°N, 134.9082°E), seamount located on the south Kyushu Palau Ridge, 2413 m, 9 January 2021, DY60 cruise of R/V ShenHaiYiHao. Other material: MBM287340, voucher specimen isolated from the holotype. Diagnosis. Polyps trumpet shaped and slightly contracted on the medial, irregularly arranged on all sides of the axis. Large needles projecting beyond the contracted tentacles. Flat and thin rods with toothed lateral edges in the tentacle rachis, longitudinally arranged. Flat rods in pinnules irregular with a slightly medial constriction. Needles/ rods obliquely arranged in the upper polyp body wall and transversely arranged in the basal part, including some flat rods. Rods/needles with abundant flat rods in coenenchyme similar to the body wall. Rods in pharynx irregular with large conical lateral projections. Description. Colony. Holotype unbranched with a disc-shaped calcareous holdfast in situ (Fig. 13A), and incomplete after collection with the holdfast not recovered, about 33 cm long (Fig. 13B). The color pink when alive and became white to light brown after fixation (Fig. 13C, D). Internodes hollow. Polyps. Polyps trumpet shaped and slightly contracted medially, always with eight large needles/rods projecting beyond the contracted tentacles, 4–8 mm in height and 2.5–4.0 mm in width (Figs. 13C, D; 14A). Polyps spaced widely on the branch, usually perpendicular to the axis, sometimes slightly tilted upward, irregularly arranged on all sides of the axis, up to 8 mm apart. Tentacles contractile and tightly folded on the distal end of the polyps. Sclerites. Flat and thin rods in the tentacle rachis are longitudinally arranged, usually with toothed to irregular lateral edges and two expanded rounded ends, measuring 109–317 × 22–60 μm (Figs. 13E, F; 14B). Their surface nearly smooth but actually covered with more or less shallow grooves. Flat rods in pinnules irregular, often with a medial constriction and shallow grooves on surface, measuring 74–134 × 24–33 μm (Fig. 14C). Eight large needles projecting beyond the contracted tentacles and forming eight sharp points, with the proximal end extending to the upper polyp body wall (Figs. 14A; 15A, B). These needles often a little curved, covered with fine conical or ridge-like and uniformly distributed warts on surface, measuring 4921–5579 × 263–321 μm (Figs. 13E, 15B). Needles/rods obliquely arranged in the upper polyp body wall and transversely arranged in the basal part, accompanied by flat rods measuring 163–3250 × 32–558 μm (Figs. 14A; 15C, D). The large needles/rods covered with conical or ridge-like and uniformly distributed warts on surface, some of them curved and branched; the small flat rods nearly smooth or with sparse warts, often with irregular edges, some elongate and scale-like. Sclerites in coenenchyme arranged along the branch, with the forms similar to those in the polyp, but relatively smaller in length, measuring 200–2250 × 33–227 μm (Fig. 14D). Among them, large needles/rods often nearly straight and covered with conical warts, some of them flat with sparse warts (Fig. 14G, H); small flat rods, similar to the tentacles, nearly smooth with slightly toothed lateral edges, some with shallow grooves or scale-like with a slightly medial constriction (Fig. 14F). Rods in pharynx small and irregular, covered with large conical or blunt projections on the lateral margins, measuring 63–117 × 25–33 μm (Fig. 14E). Type locality. Seamount located on the south Kyushu Palau Ridge, 2413 m. Etymology. The Latin adjective projectus refers to the projecting needles beyond the tentacles of this species. Genetic data. MBM287340, 28S rDNA: PP992074, cox1: PP991394, mtMutS: PP999497. Distribution and habitat. Found only from the seamount located on the south Kyushu Palau Ridge at water depth of 2413 m. Colony grows on a rocky substrate (Fig. 13A). Remarks. Dentatisis projecta sp. nov. is characterized by trumpet shaped polyps with a slightly medial constriction and large needles always projecting beyond the contracted tentacles, scales absent, and abundant rods/ needles with fine warts occur in both the polyps and coenenchyme. Dentatisis projecta sp. nov. is similar to D. bathyalis sp. nov. in the sclerites of tentacles, pinnules and pharynx, and has a close relationship with it in the mtMutS and 28S rDNA phylogenetic trees. However, it can be easily separated from D. bathyalis sp. nov. by the abundant needles/rods and absence of scales in the sclerome.