Fig 5. The inside of the S. stellaris egg case at stage 5.

A: Position of placoid denticles and caudal denticles (dorsal view). B: Body shape began to resemble an adult shark and the external yolk sac shrank visible in size (lateral view). C: The magnified head and reduced gill filaments (ventral view). The key feature for stage 5 was nearly complete loss of external gill filaments. See S5 File for original photographs of Fig 5 illustrations.