English: Representative holothuroid diversity included in this study. (a). Synapta sp. (b). Peniagone cf. vitrea. (c). Benthogone sp. (d). Pseudocolochirus violaceus. (e). Abyssocucumis albatrossi. (f). Colochirus robustus. (g). Ypsilothuria n. sp. (SIO-BIC E6221). (h). Molpadia amorpha. (i). Pseudostichopus cf. mollis. (j). Synallactidae. (k). Bathyplotes cf. moseleyi. The classification of these terminals can be found in electronic supplementary material, table S1. All photos except (g) are of the voucher specimens sequenced (catalogue numbers can be found in electronic supplementary material, table S1; further sampling information is accessible through the SIO-BIC online database, https://sioapps.ucsd.edu/collections/bi/). Images (b), (c), (i) and (k) are courtesy of the Schmidt Ocean Institute, and image (j) is courtesy of Monterey Bay Aquarium and Research Institute.