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Pocket Science – will all camouflaged cuttlefish please raise their tentacles?

Cuttlefish are masters of camouflage. Like their relatives, the squid and octopuses, they can change the colour of their skin to perfectly match a bed of pebbles, a clump of algae, or a black-and-white chessboard. I’ve written about their amazing colour-changing feats before, and the video above from the peerless Robert Krulwich shows what they can do. But their disappearing acts involve more than just colour and texture – they also use their tentacles to sell the illusion.

Cuttlefish arms are flexible tubes of muscle and can bend all the way down their length. They can hang their arms in a clump in front of their heads, or splay them out in wavy zig-zags. Now, Alexandra Barbosa from the University of Porto has shown that these postures depend on what the cuttlefish can see. She placed ten young cuttlefish in front of striped backgrounds. If the stripes ran horizontally, so did the cuttlefish’s arms. If the stripes ran vertically, they raised their first pair of arms straight up, and if the stripes ran diagonally, they held their arms at an off-vertical angle.

The cuttlefish in these images still stand out against the black-and-white walls. But against natural backdrops, the convincing nature of their raised tentacles becomes more obvious. Here are three cuttlefishes (the same animal in each pair of photos) posed normally against plastic, sand or rocks (on the left) and against algae (on the right). In the wild, scientists have reported that these animals can hold their contortions for more than 20 minutes.

Reference: Barbosa, Allen, Mathger & Hanlon. 2011. Cuttlefish use visual cues to determine arm postures for camouflage. Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2011.0196

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