Spotted on a dive by an Earth Touch cameraman off the coast of Lembeh, Indonesia, this Berry's bobtail squid (Euprymna berryi) is quite the master of disguise. These animals are tiny – and we do mean tiny – reaching lengths of just five centimetres! The miniature cephalopod looks adorable burying itself in the sand, but this behaviour is also completely necessary for its survival! 

Like most squid species, bobtail squid emerge at night to forage for crustaceans and fish. Being so small has its perks, but it also means that staying out of sight during the day is a must. To do this, the squid hide in sandy substrates, typically near seagrass beds for extra protection. 

And there's another reason for hitting the sand: bacteria. Bobtail squid have a symbiotic relationship with a bioluminescent bacterium called Vibrio fischeri. These glowing micro-organisms live in special light organs within the squids' mantle, and in return for a ride and some tasty nutrients, they help their hosts hide from predators. 

The light organ is covered by a thick, transparent tissue, and can expand and contract to diffuse the light produced by the bacteria. By directing the light downward, the stealthy cephalopod becomes nearly invisible when viewed from below, blending seamlessly against the moonlight above. 

So what does this have to do with sand? Amazingly, the squid vents 90 percent of its bacterial arsenal back into the surrounding seawater each morning. The bacteria replenishes itself during the day while the squid is buried – attracted, in part, by a sticky mucous. By evening, when it's time to feed, the squid has a new crop of helpers in tow. 

As for that sticky mucous, it also allows the squid to glue sand to their bodies, which ensures they stay hidden despite any commotion around them. 


Top header image: Nick Hobgood/Flickr