Map of collection sites A Japan and adjacent seas B Sagami Bay, Suruga Bay, and Pacific side of Honshu, and collection sites on Miura Peninsula and Yokohama C collection sites of Miura Peninsula and Yokohama D Wakaejima, Kamakura, type locality of Spirobranchus akitsushima sp. nov. E Hayama F Western part of Miura Peninsula, showing Tsurugizaki and Jogashima G Jogashima H close-up view of collection sites of Jogashima I close-up view of Tsurugizaki. Key: ○: paleo-aggregation, ●(red): current distribution. Arrow in H indicates (A) in Fig. 3; P1–P3 and C1 in I indicates site of (I) and (J) in Fig. 3.