Deima validum validum Theel , 1879

Xiao, Yunlu & Zhang, Haibin, 2024, Three new species and one new record of Deimatidae (Echinodermata, Holothuroidea, Synallactida) discovered in the South China Sea and the Mariana fore-arc area using integrative taxonomic methods, ZooKeys 1195, pp. 309-335 : 309

Deima validum validum Theel, 1879

Figs 10 , 11

Deima validum Théel, 1879: 5, figs 36-38; Théel 1882: 68-70, pls 18, 19, 31: 4-9, 36: 4, 37: 8, 43: 7, 44: 13, 46: 5; Sluiter 1901a: 60.

Deima validum validum : Hansen 1967: 488-490, fig. 5; Hansen 1975: 17-23, fig. 1, pls 11 (fig. 1), 13, (figs 1, 2); Bohn 2006: 9, fig. 4; Fernández-Rodríguez et al. 2019: 298, fig. 6.

Deima fastosum Théel, 1879: 5-6, figs 1-3; Théel 1882: 71-73, pls 20, 21: 1, 31: 10-13, 35: 7-10, 36: 7. 37: 3, 43: 2-3, 5, 46:8.

Deima blakei Théel, 1886b: 1-2, figs 1, 2; Koehler and Vaney 1905: 55-57, pl. 11: 13-15; Hérouard 1923: 40-41, pls. 5: 7, 6: 5; Deichmann 1930: 115-116, pls 10: 7-11, 11: 1-3; Deichmann 1940: 198-199.

Deima atlanticum Hérouard, 1898: 88-89, figs 1, 2.

Deima mosaicum Ohshima, 1915: 233-234.

Material examined.

Two specimens. IDSSE-2019-0630-HS01, collected from the northern slope of the South China Sea , station SY155-HS01(17°43'N, 114°13'E), depth 3451 m, 30 Jun. 2019, preserved in absolute alcohol. IDSSE-2018-0531-HS02, collected from the Xisha Trough of the South China Sea, station SY84-HS02 (18°2'N, 114°5'E), depth 3404 m, 31 May 2018, preserved at -80 °C .

Description.

External morphology. Body ovate, dorsal vaulted, ventral flattened. 9-10 cm long and average 5.5 cm wide in vivo. Skin rigid, body wall brittle and easily broken. Color orange in vivo (Fig. 10A, B ). Tentacles retracted into the mouth, resulting in uncountable quantities (Fig. 10C, D ). 12 pairs of ventrolateral tube feet contractible based on morphology of different stages, single-rowed. Five pairs of rigid and conical dorsal papillae placed in two rows. Ventrolateral papillae three pairs, half the length of the body. Pre-anal tube feet absent.

Ossicle morphology. Basal layer and several additional layers amount in the center of the perforated plates on the body wall and dorsal papillae, in diameter 0.6-1.8 mm (Fig. 11A1-B3, D1, D2 ), with regular holes and a large, reticulated knob, ~ 0.2 mm high. The tube feet with some types of developmental stages towards perforated plates (Fig. 11C1, C3 ) and perforated plates with one layer (Fig. 11C2 ), rods bearing spines (Fig. 11C4 ).

Distribution.

This subspecies probably has a cosmopolitan distribution, except for the Arctic and Southern Ocean, at depths of 724-5426 m ( Théel 1882, 1886b; Sluiter 1901a; Hérouard 1902, 1923; Koehler and Vaney 1905; Ohshima 1915; Grieg 1921; Deichmann 1940; Hansen 1975; Sibuet 1977; O’Loughlin 1998; Bohn 2006).

Remarks.

Deima validum was first described by Théel (1879) in the preliminary report of the exploring voyage of H. M. S. Challenger under Sir C. Wyville Thomson., with a detailed description of another novel species, Deima fastosum . Four new species were reported subsequently by different taxonomists: D. atlanticum Hérouard, 1898; D. blakei Théel, 1886; D. mosaicum Ohshima, 1915 and D. pacificum Ludwig, 1894. The family Deimatidae underwent a thorough revision by Hansen (1975), who regarded D. fastosum , D. atlanticum , D. blakei , D. mosaicum and D. pacificum as junior synonyms of D. validum . Hansen (1967) separated the species into two subspecies, cosmopolitan Deima validum validum and the eastern Pacific Ocean Deima validum pacificum Ludwig, 1894, based on differences in the number of dorsal papillae and the type of deposit in which they were found.

The two specimens examined here are consistent with the diagnosis of subspecies D. v. validum as described in detail by Hansen (1975). Perforated plates were like those of D. fastosum , with a large, reticulated, conical knob, which hardly ever approached in other known specimens that were used to investigate D. v. validum . This unique feature represents an extreme case of plate variation, where the spinous appearance of the skin is due to these very high and often vertically rising knobs on the plates. Hansen (1975) hypothesized that additional mesh structures on perforated plates varied with depth into two types: one-layered plates were characteristic of bathyal specimens, and many-layered plates were typical of abyssal specimens. However, it also exhibited a transitional type of plate in the abyssal Tasman Sea specimens and the bathyal Japanese specimens (perforated plates that were completely or almost completely devoid of additional meshwork), which prevented a clear distinction between a bathyal and an abyssal type of deposit.

Only in the Bay of Bengal (depth 1224-3365 m) did the development of additional layers of meshwork increase progressively with depth. In this research, high-knobbed plates were present in the abyssal South China Sea specimens (depth> 3000 m), but they were absent from the South China Sea specimens first reported (depth 1100 m) by Liao (1997). This was the second time that Deima validum has been recorded in the South China Sea. The proposition that the development of additional meshwork on perforated plates increased with depths needs to be investigated on more specimens at different depths in the South China Sea.

Figures

Figure 10. Deima validum validum (IDSSE- 2018 - 0531 - HS 02 and IDSSE- 2019 - 0630 - HS 01) A in situ image (IDSSE- 2018 - 0531 - HS 02) B in vivo image (IDSSE- 2018 - 0531 - HS 02) C dorsal view (IDSSE- 2019 - 0630 - HS 01) D ventral view (IDSSE- 2019 - 0630 - HS 01). Scale bars: 5 cm.

Figure 11. SEM images of Deima validum validum (IDSSE- 2019 - 0630 - HS 01). A 1 - A 3 dorsal body wall B 1 - B 3 papillae C 1 - C 4 tube feet D 1 - D 2 ventral body wall. Scale bars: 300 μm (A 1 - B 3); 50 μm (D 1, D 2)