Ophiocymbium tanyae Martynov, 2010

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

Ophiocymbium tanyae Martynov, 2010

Fig. 51

Material.

Clarion-Clipperton Zone • 1 specimen; APEI 1; 11.2523°N, 153.5848°W; 5204 m deep; 10 Jun. 2018; Smith & Durden leg.; GenBank: ON406633 (18S), ON406596 (28S); NHMUK 2022.74; Voucher code: CCZ_206 .

Description.

Single specimen (disc diameter = 9 mm, maximum arm length = 25 mm). Disc subpentagonal, flattened (Fig. 51A, B ). Dorsal disc surface covered with numerous, imbricated, delicate disc scales, which are irregular in shape, decrease in size distally and extend dorsally onto the first arm segments (Fig. 51C ). Radial shields and genital plates apparently absent. Disc covered by thin skin, not obscuring the scales. Ventral surface of the disc covered by scales similar to the dorsal disc scales (Fig. 51D ). Oral shield somewhat triangular, approx. as long as wide, with convex distal edge; separated from first lateral arm plate by the adoral shields. Adoral shields are wing-shaped, narrowing proximally. Each jaw bears a large, spiniform, apical papillae and a smaller adjacent one on each side; additionally, there are two to three modified papillae placed distally on each side of the jaws, block-shaped, the distalmost being wing-shaped. Genital slit is not conspicuous. Arms are thin, longer than twice the disc diameter (Fig. 51A, B ). Dorsal arm plates are triangular, wider than long, with pointed proximal and straight distal edges; separated by lateral arm plates and therefore not overlapping with preceding dorsal arm plate (Fig. 51C ). Arm spines are conical, tapering distally but with rounded tips; two arm spines on first three arm segments, three arm spines on next three segments and four on the rest; middle arm spine is the longest, but all are approx. the same length, approx. half the length of one arm segment. First ventral arm plate is triangular, while the rest are pole-axe shaped, approx. as long as wide, separated from the preceding plate by the lateral arm plates except for the first two ventral arm plates (Fig. 51D ). Tentacle pores are large and evident throughout the entire length of the arm. Three flattened, rounded, large adoral shield papillae. First four arms segments with two large papilliform tentacle scales attached to the lateral arm plate; subsequent arm segment with a single tentacle scale; tentacle scales absent on the remaining arm segments.

Remarks.

Morphological characters of the specimen are in accordance with the description of O. tanyae , which was collected in the Izu-Bonin Trench at 6740-6850 m depth. It differs from the original description in having arms ≥ 2 × as long as the disc diameter (dd), instead of being approx. the same. It also differs on the tentacle scales, which extend to the fifth segment, instead of just the third, having two tentacle scales in the first four segments instead of just one, and in the number of arm spines of the first arm segments. The number of arm spines is discussed to vary amongst the paratypes ( Martynov 2010), and it is very likely that tentacle scales are easily lost and therefore the number could differ between specimens. Only 18S and 28S were amplified for this specimen. The 28S sequence of the CCZ specimen is identical (K2P = 0%) to the sequence of the species Ophioscolecidae sp. 20 recently reported for the CCZ ( Christodoulou et al. 2020). Both specimens are recovered within the same clade, that includes other species of the order Ophioscolescida (Fig. 50 ). Ophioscolescida sp. 20, Ophiocymbium tanyae , and O. rarispinum Martynov, 2010 are recovered as a clade possibly representing the genus Ophiocymbium . The species from Christodoulou et al. (2020) was identified from DNA sequences only, as the four specimens collected (eastern IFREMER and APEI 3) are tiny juveniles with no distinctive morphological characters. The species is therefore distributed in the Izu-Bonin Trench and the Clarion-Clipperton Zone.

Ecology.

The specimen was found on the sedimented seafloor of an abyssal plain on APEI 1 at 5204 m depth.

Figures

Figure 50. Phylogenetic tree of Ophiuroidea. Concatenated (28 S, and COI) 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 51. Ophiocymbium tanyae Martynov, 2010 A dorsal view of specimen CCZ _ 206 before preservation B ventral view C detail of dorsal disc surface and dorsal arm plates D detail of jaws, ventral disc surface and ventral arm plates. Scale bars: 2 cm (A, B); 5 mm (C, D). Image attribution: Wiklund, Durden, Drennan, and McQuaid (A-D).