Table 1. Sampling information for the specimens used in this study.
| Order | Species | Family | Sampling locality |
| Echiuroinea | Echiurus echiurus (Pallas, 1767) | Echiuridae | Akkeshi, Hokkaido, Japan |
| Arhynchite pugettensis Fisher, 1949 | Thalassematidae | GenBank | |
| Ikedosoma gogoshimense (Ikeda, 1904) | Thalassematidae | Kure, Hiroshima, Japan | |
| Listriolobus sorbillans (Lampert, 1883) | Thalassematidae | Nago, Okinawa, Japan | |
| Ochetostoma erythrogrammon Leuckart & Ruppell, 1828 | Thalassematidae | Kakeroma, Kagoshima, Japan | |
| Ochetostoma sp. 1 | Thalassematidae | Kakeroma, Kagoshima, Japan | |
| Ochetostoma sp. 2 | Thalassematidae | Uken, Kagoshima, Japan | |
| Ochetostoma sp. 3 | Thalassematidae | Kakeroma, Kagoshima, Japan | |
| Thalassema owstoni Ikeda, 1904 | Thalassematidae | Kure, Hiroshima, Japan | |
| Bonellia viridis Rolando, 1821 | Bonelliidae | Itoman, Okinawa, Japan | |
| Xenopneusta | Urechis caupo Fisher & MacGinitie, 1828 | Urechidae | GenBank |
| Urechis unicinctus (von Drasche, 1881) | Urechidae | Iyosaijo, Ehime, Japan | |
| Urechis sp. 1 | Urechidae | Kashimanada, Ibaraki, Japan | |
| Heteromyota | Ikeda taenioides (Ikeda, 1904) | Ikedidae | Hakatajima, Ehime, Japan |
| Ikeda sp. 1 | Ikedidae | Ishigaki, Okinawa, Japan | |
| Outgroup | Dasybranchus sp. 1 | Capitellidae | Hakatajima, Ehime, Japan |
| Heteromastus filiformis (Claparède, 1864) | Capitellidae | GenBank | |
| Notomastus tenuis Moore, 1909 | Capitellidae | GenBank | |
| Ophelina acuminata Örsted, 1843 | Opheliidae | GenBank | |
| Lepidonotus sublevis Leach, 1816 | Polynoidae | GenBank | |
| Siphonosoma cumanense (Keferstein, 1867) | Sipunculidae | GenBank | |
| Littorina littorea (Linnaeus, 1758) | Littorinidae | GenBank | |
| Solemya velum Lamarck, 1818 | Solemyidae | GenBank |
Taxonomic classification follows Ruppert et al. (2004) [3].