Bobtail Squid
Bobtail squid rely on their mutualist bacteria Allivibrio fischerii to generate light. The bacteria inhabits a special light organ in the squid's mantle and receives sugars and amino acids in exchange for light.
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"Euprymna scolopes (Bobtail squid)."
http://en.wikipedia.org/wiki/File:Euprymna_scolopes_(Bobtail_squid).jpg
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