Dentatisis bathyalis Xu, Watling & Xu 2024, sp. nov.

Dentatisis bathyalis Xu, Watling & Xu, sp. nov. urn:lsid:zoobank.org:act: BF4C61C4-852E-4618-8BF9-FC2E82C75E8C Figs. 10–12 Material examined. Holotype: MBM287339, station FX-Dive 36 (3.7111°S, 151.8806°E), 1946 m, only some broken branches collected from the Manus Basin, 14 June 2015, the cruise of the R/V KeXue. Diagnosis. Branches dichotomously divided and emerging from the nodes. Polyps often expanded in the upper and basal part and with a medial constriction, alternately and biserially arranged. Flat and thin rods in the back of tentacle rachis longitudinally arranged. Flat rods and rodlets in pinnules with irregular edges. Needles forming a longitudinal strip between the joints of tentacles extending to the upper polyp body wall, some of them projecting beyond the tentacles. Flat and thin rods with toothed lateral edges in the upper polyp body wall longitudinally arranged. Dense scales and a few flat and thin rods in the basal polyp body wall irregularly arranged. Scales in coenenchyme dense with an obvious medial constriction. Rods in pharynx slender, covered with sparse large lateral projections. Description. Colony. Holotype incomplete and completely broken, only a few branches collected, and the holdfast not recovered, thus the colony shape unknown (Fig. 10A). The color brown after fixation, with the deepest color occurring on the distal ends of the polyps. Only one branch can be seen arising from the nodes in a pseudodichotomous manner. Internodes smooth and hollow, and the only node brown and short, concave inward, up to 0.9 mm in height. Due to the inappropriate preservation, it is unknown whether there is a layer of tegument covering on the colony. Polyps. Polyps often expanded in both the upper and basal part, and became narrow in the medial, occasionally also narrow at the base or conical, 1.5–7.0 mm in height and 1.0– 3.5 mm in width (Fig. 10B–E). Polyps well-spaced on the branch, slightly tilted toward to the distal, usually alternately and biserially arranged, occasionally uniserially arranged on one side, up to 8 mm apart. Tentacles contractile and tightly folded over the oral disc of polyps, and the sclerites forming eight obvious white longitudinal strips between the bases of tentacles extending to the upper polyp body wall (Fig. 10B, D). Sclerites. Sclerites densely arranged in polyps and coenenchyme, nearly smooth but often covered with more or less shallow grooves (Figs. 11, 12). Sclerites in the back of tentacle rachis are flat and thin rods longitudinally arranged, usually with irregular lateral edges and two rounded ends, measuring 117–224 × 18–51 μm (Fig. 11E). Sclerites in pinnules longitudinally arranged, including flat rods often with irregular edges and a slightly medial constriction, and rodlets with conical warts on lateral and lobed ends, measuring 61–150 × 14–36 μm (Fig. 11F). Needles forming white longitudinal strips between the bases of tentacles, slender of various length, some of them projecting beyond the contracted tentacles, measuring 480–2330 × 38–90 μm (Figs. 10B, D; 11A, D). Needles straight or a little curved, usually with two pointed ends, covered with conical and ridge-like warts uniformly distributed on surface (Fig. 11B). Flat and thin rods in the upper polyp body wall longitudinally arranged, usually with toothed lateral edges and two rounded ends, some of them with slightly serrated ends, measuring 160–310 × 22–70 μm (Figs. 10D, E; 11C). Dense scales and a few flat and thin rods in the basal polyp body wall irregularly arranged, elongate and often with irregular edges and a slightly medial constriction, some of them with large warts or ridge-like projections on surface and slightly serrated ends, measuring 103–274 × 26–100 μm (Figs. 10D, 12A). Scales in coenenchyme same as the basal body wall, densely arranged along the branch, usually with an obvious medial constriction and irregular edges, some of them with large warts or ridge-like projections and slightly serrated ends, measuring 96–215 × 44–111 μm (Figs. 10F, 12B). Rods in pharynx slender and irregular, covered with sparse blunt or conical projections on the lateral, measuring 173–236 × 31–58 μm (Fig. 11G). Type locality. 3.7111°S, 151.8806°E, the Manus Basin, 1946 m. Etymology. The Latin adjective bathyalis (bathyal) means this species living in the deep sea. Genetic data. MBM287339, 28S rDNA: PP992075, cox1: PP991395, mtMutS: PP999498. Distribution and habitat. Found from the Manus Basin with water depth of 1946 m. Remarks. Dentatisis bathyalis sp. nov. is characterized by slender needles forming longitudinal bands between the bases of the tentacles extending to the upper polyp body wall, dense scales in coenenchyme with an obvious medial constriction and non-toothed edges, and slender irregular rods in pharynx. These features are uncommon in the species of clade J3.