Oneirophanta cf. mutabilis Theel , 1879

Bribiesca-Contreras, Guadalupe, Dahlgren, Thomas G., Amon, Diva J., Cairns, Stephen, Drennan, Regan, Durden, Jennifer M., Eleaume, Marc P., Hosie, Andrew M., Kremenetskaia, Antonina, McQuaid, Kirsty, O'Hara, Timothy D., Rabone, Muriel, Simon-Lledo, Erik, Smith, Craig R., Watling, Les, Wiklund, Helena & Glover, Adrian G., 2022, Benthic megafauna of the western Clarion-Clipperton Zone, Pacific Ocean, ZooKeys 1113, pp. 1-110 : 1

Oneirophanta cf. mutabilis Theel, 1879

Fig. 41

Material.

Clarion-Clipperton Zone • 1 specimen; APEI 1; 11.252°N, 153.5847°W; 5203 m deep; 10 Jun. 2018; Smith & Durden leg.; GenBank: ON400724 (COI), ON406629 (18S), ON406619 (16S); NHMUK 2021.20; Voucher code: CCZ_193 .

Other material.

Indian Ocean • 3 specimens, syntypes of Oneirophanta mutabilis Théel, 1879; Eastern Indian, Antarctic Basin; 53.9167° S, 108.5833° E; 3566 m deep; Challenger Expedition, Stn. 157; NHMUK 1883.6.18.33 .

Description.

Single specimen, body uniformly white (Fig. 41A ). Body almost cylindrical,> 2 × as long as wide (L = 16 cm; W = 6.9 cm), being of almost equal breadth throughout the whole length and tapering posteriorly; mouth anteroventral and anus posteroventral. Tentacles 20, small, with a lightly brown tip, each with a terminal part with 6-8 unbranched processes. Long, pointed processes, or different lengths, arranged in four distinct rows, two rows running along the dorsal ambulacra with eight processes on each row, and the longest being approx. half of the body length (Fig. 41C ); the other two rows placed on the sides of the body, slightly above the ventral lateral ambulacra. Ventral ambulacra with 11 and 13 tube feet, arranged in two irregular rows; odd ambulacrum naked, except for two tube feet arranged in the posterior half of the body, and ten surrounding the anus; processes crowded anteriorly (Fig. 41D ). Thin skin, translucent, but hard and brittle, with numerous small and large perforated plates, with the small ones bearing two or three spines near the centre, and the large ones ~ 30 spines; ossicles imbricated, almost forming a skeleton (Fig. 41B ).

Remarks.

Sequences for the 18S, 16S, and COI genes were most similar to sequences from Oneirophanta setigera (99.07%, 95.6%, 88.51% similarity, respectively), followed by other species within the family Deimatidae (i.e., Orphnurgus glaber Walsh, 1891 and Deima validum Théel, 1879). The specimen was recovered in a well-supported clade including all members of Deimatidae (Fig. 34 ), closest to Oneirophanta sp. CCZ_100 (K2P distance: 11%). Calcareous ossicles are concordant with those in Oneirophanta mutabilis . This species was originally described west of the Crozet Islands (H.M.S. Challenger station 146: 46.7667°S, 45.5167°E) at 2514 m depth ( Théel 1879) but has been further divided in two sub-species, O. mutabilis mutabilis and O. mutabilis affinis . The former has been reported to be cosmopolitan, while the later has been recorded from the tropical eastern Pacific. Further analyses will be required to determine the validity of the subspecies and if the CCZ specimen belongs to any of those. It differs from the original description of O. mutabilis ( Théel, 1879) in having an irregular number of pedicels around the ventral surface, the pedicels around the anus arranged triangularly instead of a transversal row, as well as the arrangement of the processes on bivium and trivium. However, Théel (1879) mentioned that several of the specimens examined differed from the specimen described in the number of pedicels and the arrangement of processes, and further studies should clarify if these are indeed subspecies.

Ecology.

The specimen was found on the sediment surface of an abyssal plain on APEI 1 at 5203 m depth.

Comparison with image-based catalogue.

A very similar Oneirophanta sp. morphotype (i.e., Oneirophanta sp. indet., HOL_058) has been encountered in seabed image surveys conducted across nodule fields areas of the eastern CCZ (e.g., Amon et al. 2017b), but not in the abyssal areas surveyed at the Kiribati EEZ.

Order Elasipodida Théel, 1882

Family Psychropotidae Théel, 1882

Figures

Figure 34. Phylogenetic tree of the class Holothuroidea. Concatenated (12 S, 16 S, 18 S, 28 S, COI, and H 3) median consensus BEAST tree with posterior probability (PP) and bootstrap (BS) values indicated. Only values of PP> 0.70 and BS> 50 are shown, with values of PP> 0.95 and BS> 90 indicated with a circle. Nodes not recovered on the RAxML tree are indicated with a hyphen. Sequences generated in this study are highlighted in violet.

Figure 41. Oneirophanta cf. mutabilis Theel, 1879. Specimen CCZ _ 193 A in situ image B dorsal ossicles C dorsal view before preservation D ventral view. Scale bars: 200 μm (B); 1 cm (C, D). Image attribution: Durden and Smith (A); Bribiesca-Contreras (B); Wiklund, Durden, Drennan, and McQuaid (C, D).