Laetmogone cf. wyvillethomsoni Theel , 1979

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

Laetmogone cf. wyvillethomsoni Theel, 1979

Fig. 49

Material.

Clarion-Clipperton Zone • 1 specimen; APEI 7; 4.8877°N, 141.7569°W; 3132 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400689 (COI), ON406641 (18S); NHMUK 2021.18; Voucher code: CCZ_062 .

Other material.

Pacific Ocean • 1 specimen, holotype of Laetmogone spongiosa Théel, 1879; south of Japan; 34. 1167°N, 138°E; 1033 m deep; Challenger Expedition, Stn. 235; NHMUK 1883.6.18.47 .

Description.

Single specimen (Fig. 49A ). Body cylindrical, ~ 3 × as long as wide (L = 15.6 cm, W = 5.2 cm), with convex dorsal surface and somewhat flattened ventral surface, tapering posteriorly; mouth anterior, subventral, terminal; anus posterior, terminal, slightly dorsal; violet colouration in live and preserved specimen, with darker ventral surface (Fig. 49A-C ). Tentacles 15, of almost equal size, and very dark at the tips. Odd ambulacrum is naked; 27 or 28 tube feet arranged in a single row on each of the paired ventral ambulacra, forming a continuous line on the anterior ⅔ of the body and scattered posteriorly, also decreasing in size (Fig. 49C ). Each paired dorsal ambulacrum with a single row of long processes, 12 on the left and 13 on the right; longest processes longer than ⅓ of the body length. Twenty pedicels along each side of the ventral surface, posterior pairs smaller than the others. Fourteen processes of the bivium along the left ambulacra and thirteen along the right. Tegument is thick, completely covered by calcareous ossicles. Dorsal ossicles are wheel-like of various sizes (40-226 μm in diameter), with four or five studs, mostly five, on primary central crosses, and with 8-17 spokes, mostly eight on large wheels; ossicle is convex, rim smooth, interspoke areas small, and large central area on large wheels (Fig. 49D ).

Remarks.

Closest match on public databases for the COI gene sequence was other sequences of Laetmogone wyvillethomsoni Théel, 1879 (4.0-5.8% K2P genetic distance) from the Ross Sea and Marie Byrd Seamounts ( O’Loughlin et al. 2011). The specimen from the CCZ and specimens from L. wyvillethomsoni from Antarctica were recovered in our phylogeny (Fig. 34 ) in a well-supported clade (Fig. 34 ), which is subdivided in three clades including the two Antarctic clades stratified by depth reported in O’Loughlin et al. (2011), and the specimen from the CCZ. Type material for L. wyvillethomsoni was collected during the H.M.S. Challenger expedition at stations 300 (off the coast of South America; 33.7° S, 78.3°W; 2514 m depth) and 147 (west of the Crozet Islands; 46.2667° S, 48.45° E; 2926 m), and high morphological variability was reported ( Théel 1879). The CCZ specimen morphologically resembles L. wyvillethomsoni , but no rod-shaped ossicles were found in the dorsal skin, differing from the original description.

Ecology.

The specimen was found on the sedimented seafloor of a seamount in APEI 7 at 3132 m depth.

Comparison with image-based catalogue.

No similar laetmogonid morphotypes have been encountered in seabed image surveys conducted in the eastern CCZ or in abyssal areas of the Kiribati EEZ. Consequently, the in situ image of specimen CCZ_062 was catalogued as a new morphotype (i.e., Laetmogone sp. indet., HOL_123).

Class Ophiuroidea

To date, there are 1201 records of ophiuroids occurring at> 3000 m depth in the CCZ, with 117 representing preserved specimens ( OBIS 2022). Four specimens belonging to three different species were collected and the barcoding gene COI was amplified for all but one, for which both 18S and 28S were amplified. These sequences, excluding 18S, were included in a concatenated alignment (28S, and COI) and used to estimate a phylogenetic tree (Fig. 50 ). Ophiuroidea is amongst the most challenging groups to identify and classify based on seabed image data only; key morphological features are too small to be appropriately visualised (e.g., plates and scales) and/or are found on the ventral disc (not visible in images). As a result, the taxonomic resolution of ophiuroid morphotypes catalogued from seabed imagery is usually much lower than that in other echinoderm groups. Consequently, connectivity and distribution patterns of ophiuroids derived from seabed image data should be interpreted cautiously.

Subclass Myophiuroidea Matsumoto, 1915

Infraclass Metophiurida Matsumoto, 1913

Superorder Ophintegrida O’Hara, Hugall, Thuy, Stöhr & Martynov, 2017

Order Ophioscolecida O’Hara, Hugall, Thuy, Stöhr & Martynov, 2017

Family Ophioscolecidae Lütken, 1869

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 49. Laetmogone cf. wyvillethomsoni Theel, 1979. Specimen CCZ _ 062 A in situ image; B dorsal view of specimen before preservation C ventral view D dorsal calcareous ossicles. Scale bars: 2 cm (A); 1 cm (B, C); 50 μm (D). Image attribution: Durden and Smith (A); Wiklund, Durden, Drennan, and McQuaid (B, C); Bribiesca-Contreras (D).

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.