Plesiodiadema cf. globulosum (A. Agassiz, 1898)

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

Plesiodiadema cf. globulosum (A. Agassiz, 1898)

Fig. 32

Material.

Clarion-Clipperton Zone • 1 specimen; APEI 1; 11.2527°N, 153.5848°W; 5204 m deep; 10 Jun. 2018; Smith & Durden leg.; GenBank: ON400726 (COI), ON406628 (18S); CASIZ 229305; Voucher code: CCZ_196 .

Description.

Single specimen, with a somewhat spherical, slightly flattened test (d = 2 cm, H = 1.5 cm). In situ colouration is purple, but the inflated anal cone is greyish blue (Fig. 32A ). Primary spines are also purple, very long (up to 17 cm), thin, flexible, and strongly verticillate (Fig. 32B, C ). Pedicellariae are tridentate (Fig. 32C ).

Remarks.

In 1980, the RV Governor Ray collected several Aspidodiadematidae specimens in the CCZ at ~ 4,800 m, and were assigned to the species P. globulosum . The type localities of P. globulosum are the north of Malpelo Island, and from off Galera Point, Ecuador in the Pacific Ocean, from 2877 to 3241 m depth ( Agassiz 1898). There are no genetic sequences available on public databases for the genus, but both COI and 18S closest matches are to species of the genus Aspidodiadema A. Agassiz, 1879, within the same family (18S: 99.4% similar to A. jacobyi A. Agassiz, 1880). The COI-only tree recovered a monophyletic clade including three specimens of A. tonsum (Fig. 31 ), but the genetic divergence is within interspecific values for COI (6.5-11.7%). Despite morphological characters being in accordance with the diagnostic characters for P. globulosum , the specimen is listed as cf. as the collection site is much deeper than the type locality.

Ecology.

The specimen was collected on the sedimented abyssal plain of APEI 1, at 5203 m depth.

Comparison with image-based catalogue.

A very similar Plesiodiadema sp. morphotype (i.e., Plesiodiadema globulosum sp. inc., URC_003) has been commonly found in image-based megafauna assessments conducted in the eastern CCZ (e.g., Amon et al. 2017b) and other areas of the eastern Pacific abyss (e.g., Yuzhmorgeologiya exploration area; Kamenskaya et al. 2013; Peru Basin; Simon-Lledó et al. 2019a), both in nodule fields and in seamount areas. URC_003 is usually the most abundant echinoid encountered in image-based megafauna surveys conducted at the eastern CCZ. In contrast, URC_003 was not encountered in surveys conducted in abyssal areas of the Kiribati EEZ, where kamptosomatids (e.g., see below) appeared to dominate the echinoid community ( Simon-Lledó et al. 2019d).

Order Echinothurioida Claus, 1880

Family Kamptosomatidae Mortensen, 1934

Figures

Figure 31. Phylogenetic tree of Echinoidea. COI-only 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 32. Plesiodiadema cf. globulosum (A. Agassiz, 1898). Specimen CCZ _ 196: A in situ image B specimen after recovery C detail of pedicellaria of specimen CCZ _ 196. Scale bars: 2 cm (A); 1 cm (B). Image attribution: Durden and Smith (A); Wiklund, Durden, Drennan, and McQuaid (B, C).