Molpadiodemas stet. CCZ_194

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

Molpadiodemas stet. CCZ_194

Fig. 36

Material.

Clarion-Clipperton Zone • 1 specimen; APEI 1; 11.2517°N, 153.6055°W; 5205 m deep; 10 Jun. 2018; Smith & Durden leg.; GenBank: ON400725 (COI); NHMUK 2022.71; Voucher code: CCZ_194 .

Description.

Single specimen (Fig. 36A ). Colouration of live specimen is whitish yellow, with skin somewhat translucent (Fig. 36A, E ). Body subcylindrical in live specimen, but dorso-ventrally flattened when preserved, tapering anteriorly, ~ 4 × as long as wide (L = 25 cm, W = 8.2 cm); semi-translucent body wall, longitudinal muscles visible through it; colouration of preserved specimen is yellowish (Fig. 36E ), darker on the ventral side (Fig. 36F ). Ventral surface with small, black, unidentified epibionts embedded in the skin (Fig. 36C, D ). Specimen barely covered by sediment. Ossicles in tentacles; unbranched rods with thick central swelling; and branched rods, often with branches intertwining at the ends creating an irregular perforated mesh (Fig. 36B ).

Remarks.

The COI sequence of Molpadiodemas stet. CCZ_194 is similar to sequences of other species of Molpadiodemas , including M. villosus , M. morbillus , M. crinitus , M. involutus , and Molpadiodemas stet. CCZ_102. COI genetic divergence between both specimens collected in the CCZ is 6%, in accordance with values of genetic interspecific divergence for the genus. The specimen is recovered in a well-supported clade along with other members of the genus (Fig. 34 ), but species are not well delimited. As mentioned above, three species of Molpadiodemas have been previously reported in the CCZ ( O’Loughlin and Ahearn 2005). The tentacle ossicles from specimen CCZ_194 are very similar to those of M. helios , but this latter species is distinguished by the prominent tube feet that are barely visible in our specimen.

Ecology.

This specimen was found on the sedimented seafloor of an abyssal plain on APEI 1 at 5205 m depth.

Comparison with image-based catalogue.

A very similar Molpadiodemas sp. morphotype (i.e., Molpadiodemas sp. indet., HOL_004) has been commonly encountered in seabed image surveys conducted across nodule fields areas of the eastern CCZ (e.g., Amon et al. 2017b), but not in abyssal areas surveyed within the Kiribati EEZ.

Order Synallactida Miller, Kerr, Paulay, Reich, Wilson, Carvajal & Rouse, 2017

Family Synallactidae Ludwig, 1894

Synallactidae stet. CCZ_061

Fig. 37

Material. Clarion-Clipperton Zone • 1 specimen; APEI 7; 4.8877°N, 141.7569°W; 3132 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400688 (COI), ON406640 (18S); NHMUK 2022.75; Voucher code: CCZ_061.

Description. Single specimen; description of external morphological features only from in situ image as the specimen was damaged during collection (Fig. 37A ). Body semi-circular, with ventral surface flattened, tapering distally; very wide, widest part of body ~ 7 cm; anus posterodorsal; mouth anteroventral. Tegument seems thick. Ossicles present in tentacles, slightly curved rods, <250 μm (Fig. 37B ).

Remarks. There are no close matches to the COI sequence of Synallactidae stet. CCZ_061 in public databases. The closest match is to Synallactidae stet. CCZ_066 (14% K2P). Both specimens are recovered in a well-supported clade representing the family Synallactidae (Fig. 34 ). They are recovered very close to Paelopatides Théel, 1886, but COI divergence suggest they belong to different genera.

Comparison with image-based catalogue. No similar Synallactidae morphotypes have been so far catalogued from seabed imagery collected in the eastern CCZ or in abyssal areas of the Kiribati EEZ. Consequently, the in situ image of Synallactidae stet. CCZ_061 was catalogued as a new morphotype (i.e., Synallactidae gen. indet., HOL_120).

Ecology. This specimen was collected on the sedimented seafloor of a seamount in APEI 7 at 3132 m depth.

Synallactidae stet. CCZ_066

Fig. 38

Material. Clarion-Clipperton Zone • 1 specimen; APEI 7; 4.8896°N, 141.75°W; 3095 m deep; 27 May. 2018; Smith & Durden leg.; GenBank: ON400692 (COI), ON406642 (18S); NHMUK 2022.63; Voucher code: CCZ_066.

Description. Single specimen, body semi-circular with ventral surface flattened; ~ 3 × longer than wide (L = 21 cm, W = 6 cm; Fig. 38A ). Mouth anteroventral, anus posterodorsal. Colouration in live specimen is bright red (Fig. 38D, E ). Specimen severely damaged during collection, guts separated from skin. Tegument is thick and leathery, with wart-like protrusions on the dorsal surface, more evident on live specimen (Fig. 38A ), and with a small, very short, triangular dorsal appendage. Brim evident on ventral surface. Small tube feet arranged in two irregular rows, one on each side of ventrum, running longitudinally. Tentacles 18. Ossicles present in dorsal skin (Fig. 38B ) and tentacles (Fig. 38C ).

Remarks. There are no close matches to the COI sequence of Synallactidae stet. CCZ_066 in public databases. The closest match is to specimen Synallactidae stet. CCZ_061 (14% K2P). Both specimens are recovered in a well-supported clade representing the family Synallactidae (Fig. 34 ). They are recovered very close to Paelopatides Théel, 1886, but COI divergence suggest they belong to different genera.

Ecology. This specimen was collected on the sedimented seafloor of a seamount on APEI 7 at 3095 m depth.

Comparison with image-based catalogue. No similar Synallactidae morphotypes have been so far catalogued from seabed imagery collected in the eastern CCZ nor in abyssal areas of the Kiribati EEZ. Consequently, the in situ image of CCZ_066 was catalogued as a new morphotype (i.e., Synallactidae gen. indet., HOL_121). The dorsal protrusions that differentiate HOL_121 from HOL_120 may not be clearly visible in vertically-facing seabed imagery, and hence these two taxa might only be classifiable into a single, generic morphotype (i.e., HOL_120) in quantitative analyses.

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 36. Molpadiodemas stet. CCZ _ 194 A in situ image B tentacle ossicles C epibionts on ventral surface D detail of epibionts E dorsal surface F ventral view of specimen before preservation. Scale bars: 2 cm (A); 25 μm (B); 1 cm (E, F). Image attribution: Durden and Smith (A); Bribiesca-Contreras (B-D); Wiklund, Durden, Drennan, and McQuaid (E, F).

Figure 37. Synallactidae stet. CCZ _ 061 A in situ image B tentacle ossicles. Scale bars: 2 cm (A); 50 μm (B). Image attribution: Durden and Smith (A); Bribiesca-Contreras (B).

Figure 38. Synallactidae stet. CCZ _ 066 A in situ image B ossicles on dorsal skin C tentacle ossicles D dorsal surface E ventral surface of specimen before preservation. Scale bars: 2 cm (A, D, E); 50 μm (B, C). Image attribution: Durden and Smith (A); Bribiesca-Contreras (B, C); Wiklund, Durden, Drennan, and McQuaid (D, E).