 Unlike many bioluminescent marine organisms, Etmopteridae bioluminescence does not come from symbiotic relationships with bioluminescent bacteria, but from their own light-producing organs called photophores.The ventral side of the sharks contains many photophores.Each photophore contains several light-producing vesicles called photocytes and photophores also have an iris-like structure that may allow sharks to control the level of light they produce.