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Alex_Mustard

Neck crab arm waving

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I photographed this neck crab in Cayman. I didn't spend long with it because it was deepish and nearby there were a pair of pink clingfish which I hoped might mate (they didn't). Anyway, in most of pictures of this crab, it is waving its arm in the air (water). The arm is covered in feathery hydroids and I can't help thinking that this would be a pretty efficient net for catching particles for the crab.

Do you think it was doing this intentionally, or just a coincidence of when I happened to take the photo?

 

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Looking through my library of neck crab images I have lots of shots of them when not all their legs are touching the fan or black coral they are living on. Although none as obviously being waved around as this one. But it often seems to be these long first legs that are not holding on, but out in the current.

 

Alex

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Given your affinity and ability to approach critters, he was probably waving back at you Alex.

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Given your affinity and ability to approach critters, he was probably waving back at you Alex.

 

Or giving me the finger...

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It's certainly possible. Boxer crabs sweep their anemones over surfaces to pick up food particles which they then take from the anemones. Arm waving could make them look more like a collection of hydroid branches for better camouflage. Last possibility is that he really was trying to get your attention & get into one of your books.

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Many of the Decorator Crabs with small anemones all over their bodies that I watch here in Lembeh seem to always be brushing, collecting then eating the particles that get stuck on these decorations, so it's definitely likely.

 

I also observe the Hairy Squat Lobsters doing the same with particles getting trapped in their hairs. They have a back pair of almost invisible non-hairy legs which they run over their bodies, collecting the particles, which they then eat. I'm presuming this is why Hairy Squat Lobsters are hairy. You can see this if you look closely on this video

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Thank you!

 

I have had a more careful look through more of my neck crab pictures and in most of them these longer first legs are usually not touching everything. Although not as obviously sticking out as in the first image.

 

There might be something in this. Or it might just be a quirk of the angle I took the photo from. I will make a point of watching them next time I shoot them.

 

Alex

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