This little creature is known as a clusterwink snail.
The tiny (about the size of a fingernail) sea snail gives off green luminescent light flashes to scare away predators. The flashes trick the enemy by making the snail look larger. The thick, heavy, opaque shell acts as a powerful reflector.
The clusterwink snail is found along the New Zealand and Australian rocky shores. When the tide is out, the snails cluster together, hiding under rocks and in crevices. When the tide comes in, they journey out to graze on algae.
Embryos of the snail are incubated in a brood chamber located internally behind the female head. When mature they are expelled into the sea.
Several research studies are being done to learn the biological cause of the luminescence and how the shell works to reflect.
Below shows the snail at rest and in danger mode.