egg capsule of Diphyllobothrium latum, the fish tapeworm. This egg
capsule often displays a button on the non-opercular end (seen to the lower
portion of the image). The enclosed embryo will develop into a coracidium,
a ciliated, free-swimming larva which must be eaten be a copepod, such as Diaptomus
or Cyclops in order to continue the life cycle. 400x