Bathyplotes liaoi, Xiao & Xiao, 2025

Bathyplotes liaoi sp. nov.

Figs 6 View Figure 6 , 7 View Figure 7 , 8 View Figure 8

Material examined.

Holotype • West Pacific, the Y 3 Seamount near the Yap Trench , Dive FX-Dive 21 (8°51'N, 137°47'E), depth 344 m, 24 Dec. 2014, preserved in 95 % ethanol, CN: Y 30165, RN: MBM 286918 View Materials . GoogleMaps

Diagnosis.

Body elongated, dorsally convex, ventrally flattened. Mouth ventral, anus dorsal. Tentacles 18. Dorsal papillae arranged in six longitudinal rows. Brim formed by small ventrolateral papillae. Tube feet irregularly scattered on the ventral surface. Dorsal body wall containing tables with cross-shaped discs, four (rarely five) pillars of tables bearing numerous large spines, and four to six transverse beams; small tables with annular discs; perforated plates. Dorsal papillae with perforated plates, tables with cross-shaped discs, and support rods. Ventral body wall ossicles similar to those in the dorsal body wall, except for some tables with much higher spires. Tube feet with perforated plates, irregularly shaped ossicles, and small tables with annular discs. Tentacles with spiny rods.

Description.

Body elongated, slightly pointed at each extremity, dorsal slightly arched, ventral flattened (Fig. 6 A – C View Figure 6 ). Color in life faint yellow, sub-transparent, dorsal papillae, tube feet, and tentacles darker (Fig. 6 B, C View Figure 6 ). Body 15 cm long and 5 cm wide before fixation (Fig. 6 B, C View Figure 6 ). Mouth ventral, anus dorsal and surrounded by numerous small papillae (Fig. 6 B, C View Figure 6 ). Peltate tentacles 18. Dorsal surface densely covered with approximately equal conical papillae, arranged in six longitudinal rows, with ~ 14–18 papillae in each row (Fig. 6 A, B View Figure 6 ). The jagged edges on both sides of the body formed by a single row of numerous smaller papillae. Tube feet irregularly arranged longitudinally throughout the ventral sole, ~ 86 in each row. Ossicles. Tables of two types in the dorsal body wall (Fig. 7 A 1 – A 7 View Figure 7 ): 1) Cross-shaped discs (Fig. 7 A 1 – A 4 View Figure 7 ) with four arms, each arm bearing small spines, 100–200 μm in length, with a number of perforations at the ends, four (rarely five) pillars bearing numerous large spines, four to six transverse beams, the spires measuring 108–200 μm in height, tips formed by fused pillars. 2) Annular discs (Fig. 7 A 5 – A 7 View Figure 7 ) with four large holes formed by simple diagonal bars, discs ~ 58 μm in diameter, the spires 30–42 μm high, with one or two transverse beams. Dorsal papillae with most tables (Fig. 7 B 1 – B 4 View Figure 7 ) similar to those of the dorsal body wall (first type), rarely smaller tables with four transverse beams (Fig. 7 B 4 View Figure 7 ); perforated plates, measuring 400 μm in diameter (Fig. 7 B 5 View Figure 7 ); spinous rods up to 366 μm in length (Fig. 7 B 4 View Figure 7 ). Ventral body wall tables with four-armed discs, small tables with annular discs, and perforated plates (Fig. 7 C 1, C 2 View Figure 7 and Fig. 8 View Figure 8 ), most ossicles of similar features to those in the dorsal body wall, except that a few tables with really high spire, measuring 245 μm in height (Fig. 8 A, B View Figure 8 ). In tentacles (Fig. 7 D View Figure 7 ) rods 70–500 μm long. Tube feet with four types of ossicles: 1) perforated plates (Fig. 7 E 1 View Figure 7 ); 2) smaller tables with annular discs (Fig. 7 E 2 – E 7 View Figure 7 ), ~ 88 μm in diameter, the spires of tables higher than those in the dorsal body wall (second type), measuring 48–64 μm high, four spiny pillars with three transverse beams; 3) rods up to 404 μm in length (Fig. 7 E 8 View Figure 7 ).

Type locality.

The Y 3 Seamount near the Yap Trench, tropical Western Pacific, 344 m depth.

Etymology.

The species is named after one of the pioneers in the study of holothuroid fauna in China, Professor Yulin Liao.

Distribution.

Only known from its type locality.

Remarks.

The predominance of four-pillared tables undoubtedly indicates that this species belongs to the Bathyplotes . Bathyplotes liaoi sp. nov. is mostly similar, in terms of ossicle types, to Bathyplotes patagiatus Fisher, 1907 , which has been regarded as a synonym of Bathyplotes natans . Both species share the presence of ossicles that include four-armed crosses, small tables with annular discs, and spinous rods. However, the new species can be distinguished from B. patagiatus by the presence of tube feet on the midventral radius and differences in the shape of the spires of tables. In Bathyplotes liaoi sp. nov., the tables typically have four, rarely five pillars, with their dilated ends of spires usually formed by these fused pillars, rather than expanding into a crown. In contrast, the tables in B. patagiatus are robust, with each table possessing four pillars and a broad thorny crown formed by the highly dilated spire ends, resembling a quadrilateral tower. Moreover, the pillar ends in B. patagiatus are often unfused. The new species also differs from B. patagiatus by the presence of tables with annular discs and five-pillared crosses in the dorsal body wall, as well as perforated plates in the ventral body wall and papillae. In B. liaoi sp. nov., the arms of the crosses bear small spines, whereas those in B. patagiatus are smooth. The spines on the spires of tables in B. liaoi sp. nov. are distributed along the entire length of the pillars, while in B. patagiatus , the spines are confined to the upper half, even in tables with exceptionally long spires. In addition, B. liaoi sp. nov. lacks C-shaped ossicles present in B. patagiatus .

Both Bathyplotes liaoi sp. nov. and B. phlegmaticus have two types of tables in the body wall: 1) large tables of characteristic form, with cross-like discs and 2) smaller tables with annular discs. The arms and pillars of both types of tables possess spines. However, the new species exhibits several key differences from B. phlegmaticus : 1) The number and arrangement of papillae are different. In B. liaoi sp. nov.: the dorsal surface was densely covered with conical papillae of approximately equal size, arranged in six longitudinal rows, with ~ 14–18 papillae each row. The jagged edges along both sides of the body were formed by a single row of numerous smaller papillae. In B. phlegmaticus , a delicate rim was formed by free papillae, with ~ 35 at the anterior part of the body and ~ 12 along the anterior and posterior lateral edges. Papillae on the ventral side are few, irregularly distributed, and not confined to the radii. 2) Tube feet in B. phlegmaticus have rods and a well-developed endplate. However, tube feet in B. liaoi sp. nov. include tables with annular discs, irregular large ossicles, rods, and a plate. 3) Tables have different numbers of transverse beams. In B. phlegmaticus , the spires of large tables possess 6–8 transverse beams, while smaller tables have 1–3 transverse beams. In B. liaoi sp. nov., the large tables have fewer transverse beams (4–6), and the smaller tables have only one or two transverse beams.