Bathyplotes varicolumna Xiao & Xiao, 2025, sp. nov.

Bathyplotes varicolumna sp. nov. Figs 4, 5 Material examined. Holotype • West Pacific, the M 4 Seamount located in the Caroline Ridge, Dive FX-Dive 137 (10°35.04'N, 140°07.27'E), depth 1195 m, 21 Aug. 2017, preserved in 95 % ethanol, CN: C 144, RN: MBM 286925. Diagnosis. Body elongated, ventrally flattened. Mouth ventral, anus terminal. Peltate tentacles 16. Dorsal surface with scattered large papillae and laterally with a simple row of small papillae. The dorsal side irregularly arranged with several low ‘ fungiform’ whitish warts. Ventral surface with scattered minute tube feet. Dorsal body wall lacking ossicles. Papillae cross-shaped tables and rods, tables with 4–7 arms, 3–5 pillars, and without transverse beams. Cross-shaped tables with single pillars in low whitish warts. Cross-shaped tables with single pillars, support rods, and irregular shaped ossicles in the ventral body wall. Cross-like discs of tables, perforated plates, and support rods in ventral tube feet. Rods, smaller tables, and irregular deposits in tentacles. Description. Body elongated, ventrally flattened, body wall thin and pliable. Color pale pink in situ, and orange in life (Fig. 4 A, B). Body 24 cm long and 6.5 cm wide in living specimen (Fig. 4 C, D). Mouth ventral, anus terminal. Peltate tentacles 16. Circum-oral papillae present (Fig. 4 B). Bivium with some scattered large papillae and laterally with a simple row of small papillae (Fig. 4 A, C). A number of low whitish warts arranged along the two dorsal interradii (Fig. 4 C). Trivium with some scattered minute tube feet (Fig. 4 B, D). Ventral surface with three series (a middle series and one lateral series on each side) of tube feet (Fig. 4 D), the middle series forming multiple rows, occupying a third of the ventral surface, other two series forming two or three rows on each side. Brim narrow and retracted, formed by ventrolateral papillae (Fig. 4 A, B). Ossicles. Dorsal body wall lacking ossicles. Dorsal papillae with tables and rods (Fig. 5 A), cross-shaped discs of tables 190–260 μm across, with 4–7 arms, each arm ~ 45–155 μm long, the ends of the arms enlarged and pierced with holes, the spires composed of 3–5 pillars, without transverse beams, the top of pillars fused, making the tip of spires spinous; rods curved, 280–315 μm long. Ventral body wall with tables, rods and irregularly shaped ossicles (Fig. 5 B), cross-shaped discs of tables with four arms, and only one central pillar (often truncated); rods up to 95 μm. Cross-like discs of tables in ventral tube feet 100–222 μm across, with 1–4 pillars, without transverse beams, the top of pillars fused; terminal plates and rods also in tube feet (Fig. 5 C). Rods, smaller tables, and irregular deposits in tentacles (Fig. 5 D). Tables with four arms in low whitish warts similar to those in the ventral body wall, and possessing only one central pillar, the top of pillars often irregularly branched or truncated (Fig. 5 E). Type locality. The M 4 Seamount located in the Caroline Ridge of the tropical Western Pacific, depth 1195 m. Etymology. The Latin word varicolumna means ‘ various pillars’ and is used to describe tables characterized by different types of pillars. Distribution. Only known in its type locality. Remarks. The body of the new species, with a sole-like ventral side, and its tables featuring cross-shaped discs with typically three or four pillars, confirm its placement within the genus Bathyplotes. In most Bathyplotes species, tables generally possess four pillars, rarely three or five. However, in the new species, tables exhibit a broader variation, with 1–5 pillars, and 4–7 arms, an uncommon variation within this genus. Among the known species of Bathyplotes, the morphology of Bathyplotes varicolumna sp. nov. most closely resembles that of B. moseleyi. Both species share tables with numerous arms and dorsal interradii bearing numerous low whitish warts. Nonetheless, the new species can be distinguished from B. moseleyi by the following differences: 1) Both B. moseleyi and the new species possess three series of tube feet on the ventral surface: a middle series and one lateral series on each side. However, the middle tube feet in B. moseleyi are arranged in a thin double row, whereas the middle tube feet in B. varicolumna sp. nov. are scattered irregularly and broadly along the midventral radius. 2) In B. moseleyi, tables have discs with 4–8 arms, and their spires are formed by four pillars and one, rarely two transverse beams, or are often entirely devoid of transverse beams. In contrast, the tables in B. varicolumna sp. nov. have discs with 4–7 arms, and their spires consist of 1–5 pillars without transverse beams. 3) The tube feet of B. moseleyi contain support rods, whereas those of B. varicolumna sp. nov. possess tables and terminal plates in addition to rods. 4) In B. moseleyi, whitish warts contain only a few rods at their ends. In B. varicolumna sp. nov., however, the predominant ossicles are four-armed tables with cross-shaped discs, supported by a single central pillar that is often irregularly branched or truncated at the top.