Heteropods like this Carinaria are some of the very few planktonic organisms which are not bioluminescent. However they still must deal with luminescence: Notice that the gut (the pink stripe below the eye) is pigmented, and is oriented vertically, probably to minimize its silhouette. (See the pteropod below for another non-luminous mollusc, and the squid for a mollusc which is luminescent.)

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