(photo found here)

This is a bobtail squid (Euprymna berryi). These squid have a spherical body, two large rounded fins at the posterior end, and large eyes. A layer of iridescent cells give them their typical blue-green color. Bobtail squid have a symbiotic relationship with bioluminescent bacteria (Vibrio fischeri), which inhabit a special light organ in the squid’s mantle. The bacteria are fed a sugar and amino acid solution by the squid and in return hide the squid’s silhouette when viewed from below by matching the amount of light hitting the top of the mantle. The organ contains filters which may alter the wavelength of luminescence closer to that of downwelling moonlight and starlight. They are found predominantly in the Pacific Ocean. Squid belong to the phylum mollusca (see this previous post) and the class cephalopoda (see this previous post).

(Source/Source)