Amphigymnas ganquani, Xiao & Xiao, 2025

Xiao, Yunlu & Xiao, Ning, 2025, Description of four new synallactid species (Holothuroidea, Synallactida, Synallactidae) from the tropical Western Pacific Ocean, ZooKeys 1231, pp. 347-370 : 347-370

Amphigymnas ganquani sp. nov.

Figs 9 , 10 , 11

Material examined.

Holotype • West Pacific, the Ganquan Plateau in the SCS , depth 1350 m, 12 May 2018, preserved in 95 % ethanol, CN: GQHT-SY-066-12, RN: MBM 286926 .

Diagnosis.

Body elongated, cylindrical, gradually tapering at both ends. Color yellowish white. Skin fragile, glass-like. Mouth ventral, oral disc with front-suspended dorsal papillae, anus terminal. Peltate tentacles 20. Dorsal papillae arranged in two rows along each dorsal ambulacrum. Ventrolateral papillae arranged in a single row. Ventrolateral tube feet arranged in a single row on each side. Midventral ambulacrum placed in alternate two rows. Dorsal body wall tables with short or high 4 - pillared spires and 0–2 transverse beams. Papillae tables and widened midrods, tables with higher spires, four or more usually fused pillars, and three or four transverse beams. Ventral body wall with smaller tables, spires truncate, without transverse beams. Tube feet tables with truncate and high pillars. Tentacles support rods.

Description.

Body long and cylindrical, slightly slender at both ends (Fig. 9 A, B ), ventral flattened. Body 28 cm long, 2.5 cm wide mid-body before fixation (Fig. 9 C ). Color yellowish white, body wall thin, calcareous, and fragile. Mouth ventral, anteriorly overhung by a few dorsal papillae (Fig. 9 C, D ), anus terminal. Peltate tentacles 20, measuring 0.25–0.3 cm in diameter after fixation (Fig. 9 D ). Two paired conical papillae placed in a single series on each dorsal radius (four rows across dorsally), each up to 1 cm long after fixation. Ventrolateral papillae arranged in a single row, ~ 22 on each body side, up to 1.5 cm long after fixation. Irregular tube feet relatively large and placed in single rows on ventrolateral radii, ~ 60 in each row. Midventral tube feet small, placed in alternate two rows, ~ 80 in each row. Longitudinal muscles undivided, tentacle ampullae absent, and gonads arranged in clusters. Ossicles. Dorsal body wall tables (Fig. 10 A – J ), discs perforated plates, edges usually incomplete, 220–370 μm across, with numerous perforations of similar size, spires with four pillars (mainly) or more pillars (Fig. 10 G, H, J ), short or relatively high, lacking or possessing one (rarely) or two transverse beams. Short pillars lacking or with one beam, ~ 50–80 μm in length (Fig. 10 A – C, F – J ), relatively high pillars with two beams, 100–120 μm in length (Fig. 10 D, E ). Spires of tables in dorsal and lateral papillae possessing much higher and firmer spires (Fig. 10 K – W ) than those in dorsal body wall, discs up to 400 μm across, with four large central perforations and many small outer perforations, four or more pillars, up to 150 μm in length, usually fused, making the number of transverse beams uncertain, some spires of tables possibly possessing 3–4 transverse beams; widened midrods in papillae up to 600 μm long, with marginal projections (Fig. 10 X ). Ventral body wall with smaller tables (Fig. 11 A ), discs 144–267 μm across, edges more complete and smooth, spires truncate, without transverse beams. Tentacles predominantly rods, curved, bearing irregular marginal projections, up to 803 μm long (Fig. 11 B ). Tube feet support rods straight to curved, widened midrods bearing irregular marginal projections, some placing through the entire length (Fig. 11 C – E ); tables with truncate pillars (Fig. 11 F ), without transverse beams; tables with high pillars, possessing four beams (Fig. 11 G ).

Type locality.

The Ganquan Plateau in the South China Sea, tropical Western Pacific, depth 1350 m.

Etymology.

The specific name refers to the Ganquan Plateau, where the holotype was sampled.

Distribution.

Currently known from the type locality.

Remarks.

The new species belongs to Amphigymnas Walsh, 1891 , characterized by the glass-like body wall formed by numerous large tables, large conical papillae on the dorsal and ventrolateral radii, and a midventral row of small tube feet filled with many support rods.

The new species differs from the A. bahamensis Deichmann, 1930 by the arrangement of ventral tube feet and the number of pillars of dorsal tables. Dorsal tables in the new species have at least four pillars, whereas those of A. bahamensis have rare 3 - pillared truncate spires. Additionally, the ventral tube feet in the new species are arranged along both the ventrolateral and midventral radii, while those in A. bahamensis are restricted to the midventral radius. The external morphological differences between the new species and Amphigymnas woodmasoni are slight. However, the new species can be distinguished primarily by ossicle features: Tables in A. woodmasoni have four large central perforations surrounded by many smaller peripheral holes, and the spires of tables are usually rather primitive and reduced to four spines (without forming pillars) on the body walls and papillae. In contrast, the spires of tables on body walls and papillae in the new species are relatively high and often exhibit four or more pillars, rather than being reduced to spines. Notably, in the papillae they can reach heights of up to 150 μm. In comparison to Amphigymnas staplesi O’Loughlin in O’Loughlin et al. 2013, the new species exhibits several distinguishing characteristics: The oral disc of A. staplesi is surrounded by a continuous series of papillae, whereas the new species has only front-suspended dorsal papillae. The new species is quite different from A. staplesi by the ossicle features: 1) In A. staplesi , the tables of dorsal body wall have discs with four large central perforations and many smaller outer perforations, and the spires have four pillars and two transverse beams. In the new species, the dorsal tables have discs with perforations of approximately equal diameters, and the spires have four or more pillars and 0–2 transverse beams; 2) The pillars of the new species are relatively higher, sturdier, and often irregularly fused, distinguishing them from those in A. staplesi ; 3) Additionally, the new species possesses support rods, which are absent in A. staplesi ; 4) The new species lacks endplates in its ventrolateral tube feet, whereas A. staplesi possesses endplates.

The genus Amphigymnas was newly recorded in the SCS, and the discovery of the new species expands the geographical distribution of this genus.

Figures

Figure 9. Amphigymnas ganquani sp. nov. holotype: MBM 286926 A, B in situ images C holotype after fixation D tentacles. Scale bars: 1 cm.

Figure 10. SEM images of Amphigymnas ganquani sp. nov. holotype: MBM 286926. Ossicles from A – J dorsal body wall K – X dorsal and lateral papillae. Scale bar: 100 μm.

Figure 11. SEM images of Amphigymnas ganquani sp. nov. holotype: MBM 286926. Ossicles from A ventral body wall B tentacles C – G tube feet. Scale bars: 100 μm (A, E – G); 300 μm (B – D).