Fig. 1

Stereomicroscopy images of living specimens of Ramisyllis kingghidorahi and in situ underwater photography of its host sponge Petrosia sp. A, Fragment of the anterior region including the prostomium, proventricle, and first branches, dorsal view. Arrowhead points to the anterior end. B, Host sponge Petrosia sp. in its natural habitat [modified from 54]. C, Fragment of a R. kingghidorahi specimen including several posterior ends. Arrow points towards the direction of the anterior end, which is missing. D, Developing male stolon attached to its parental stalk. Dashed line indicates the boundary between the stalk (left) and the stolon (right). Scale bars: 2 mm (A, C); 1 cm (B); 250 µm (D)