If you were to find eggs like this one in the plankton or in a tide pool, you could be sure they belonged to a chiton: chiton eggs are easily distinguished by the elaborately ruffled, multi-faceted hulls that surround them.  The mossy chitons of the genus Mopalia are found intertidally on rocks and on hard substrata in the harbor.  These chitons are called “mossy” because the girdle, which surrounds the eight valves on its dorsal surface, is covered in stiff hairs, resembling its namesake moss. 

The hull is basically just an especially fancy eggshell, out of which the larva must hatch.  Culture dishes of Mopalia that have been successfully reared through hatching are littered with empty hulls, intact save for a very small hole through which the swimming larva made its escape.  Instead of digesting the entire eggshell, Mopalia’s larva somehow cracks away just one or a few of the hull facets and squeezes through the gap.  It’s remarkable that the larval epithelium, which only hours ago was a series of loosely connected cells, remains intact even after squirting itself through the hull like toothpaste from a tube!

— text by Katie Bennett & George von Dassow