Oneirophanta mutabilis mutabilis 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

Oneirophanta mutabilis mutabilis Theel, 1879

Figs 8 , 9

Oneirophanta mutabilis Théel, 1879: 6-7, figs 4-6; Théel 1882: 62-68, pls XXI: 2, XXII, XXXI: 1-3, XXXVI: 1, 2, 8-11, XXXVII: 4, 13, XXXVIII: 11-12, XL: 1-3, XLI: 1, 2, 4, XLII: 9, XLIII: 1, 6, XLV, XLVI: 6, 7; R. Perrier 1902: 374-380, pl. XVIII: 10-15; Grieg 1921: pl. II: 1, 2; Hérouard 1923: 39-40, pls IV: 10, V: 3, 4; Agatep 1967: 63-65, pl. X: 1-7.

Oneirophanta mutabilis mutabilis Théel: Hansen 1967: 485-488, figs 3, 4; Hansen 1975: 24-32, figs 2-5.

Oneirophanta alternata R. Perrier, 1900: 117-118; R. Perrier 1902: 380-386, pls XIV: 3, 4, XVIII: 16-22.

Oneirophanta alternata var. talismani R. Perrier, 1902: 386-388, fig. 6.

Material examined.

One specimen. IDSSE-2020-1203-HS01, in the Mariana fore-arc area, western Pacific Ocean, station SY310-HS01 (11°41.42'N, 140°58.56'E), depth 3394 m, 3 Dec. 2020, preserved in absolute alcohol .

Description.

External morphology. Body cylindrical, nearly equal in width throughout the whole length and tapering anteriorly. 15 cm long and 4.5 cm wide after fixation with 95% alcohol for several days (Fig. 8A, B ). Skin white, calcified and brittle. Tentacles 20, unretractile, 0.6-1.6 cm in length, with 7-9 marginal digits. Mouth and anus ventral. Ventrolateral ambulacra with 16 tube feet on each side, arranged in two irregular rows. Dorsal papillae 6 pairs, the maximum length up to 10 cm, placed in single rows along dorsal radii. Ventrolateral papillae 13 on each side, the maximum length up to 6 cm. Midventral tube feet not found due to damage to the mid-abdomen of the specimen, and only approximately six small tube feet observed near the anus.

Ossicle morphology. The body wall and papillae with perforated plates (Fig. 9A1-C3 ), 0.9-1.5 mm in diameter. The entire periphery of fully developed plates usually surrounded by closed holes, with large central holes (especially in ventrum) and small peripheral holes. Some plates bearing 8-14 small, vertical spines (Fig. 9B1, C3 ), but no formation of a secondary layer of meshwork. Tube feet with rods up to 0.8 mm long (Fig. 9D1, D2, D4 ) and incompletely developed plates with open ramifications (Fig. 9D3, D5 ). The irregular rods in tentacles with variable bending angles (Fig. 9E1-E5 ).

Distribution.

Cosmopolitan, depth 2515-6000 m ( Hansen 1975, 1967; Thandar 1984).

Remarks.

Oneirophanta mutabilis was first described west of the Crozet Islands (H.M.S. Challenger station 146: 46°46'S, 45°31'E) at depths of 2514 m ( Théel 1879). It was divided into two subspecies, Oneirophanta mutabilis mutabilis Théel, 1879 and Oneirophanta mutabilis affinis Ludwig, 1893, based on differences in tentacle shape, the type of deposit, and the number of dorsal papillae ( Hansen 1967). There are four main distinctions between them (see Table 2 ): (1) O. m. affinis was restricted to a relatively small area in the eastern Pacific where it replaced the otherwise cosmopolitan O. m. mutabilis . (2) tentacles with marginal digits were found in all specimens examined of O. m. mutabilis , but tentacle discs of O. m. affinis were smooth or had incised edges, and they lacked marginal digits. (3) the perforated plates of O. m. affinis were almost completely devoid of vertical spines, whereas those of O. m. mutabilis had vertical spines. (4) numerous rods of O. m. affinis were usually present in the tentacle discs, which was an additional difference from O. m. mutabilis . The morphological characteristics of our specimens were in accordance with the description of O. m. mutabilis ( Hansen 1975). This was the first record of O. m. mutabilis from the Mariana fore-arc area.

Genus Deima Théel, 1879

Figures

Figure 8. Oneirophanta mutabilis mutabilis Theel, 1879 (IDSSE- 2020 - 1203 - HS 01) A dorsal view B ventral view. Scale bar: 3 cm.

Figure 9. SEM images of Oneirophanta mutabilis mutabilis Theel, 1879 (IDSSE- 20201203 - HS 01). A 1, A 2 dorsal body wall B 1, B 2 dorsal papillae C 1 - C 3 ventral body wall D 1 - D 5 tube feet E 1 - E 5 tentacle. Scale bars: 300 μm (A 1 - C 3); 100 μm (D 1 - E 1, E 3 - E 5); 50 μm (E 2).