Bobtail Squid playing in the sandbox
This is Euprymna berryi. A layer of iridescent cells gives this squid its gorgeous glowing blue/green coloration. When chromatophores expand within these cells, the squid can turn completely brown to blend with its sandy surroundings. E.berryi also has formed "a symbiotic relationship with bioluminescent bacteria (Vibrio fischeri), which inhabit a special light organ [on] the squid's [underside]." (Wikipedia) At night when bobtails are active, "the organ contains filters which may alter the wavelength of luminescence closer to that of downwelling moonlight and starlight" so that bottom-dwelling predators will not spot this stealthy squid swimming overhead. Very cool!