Carry On, Carry Crab

Carry crab with sea pen Anna DeLoach
Carry Crab with a live (for now) sea pen (a soft coral)

I love carry crabs! These little crabs of the family Dorippidae, have modified back legs that they use to grip things, living or inanimate, to disguise themselves. Last month, I posted video of one that I saw years ago, stumbling around with a live, writhing nudibranch. In 1999, on a night dive in Lembeh Strait Indonesia, I saw a tissue box run across the sand. I knew nothing about “carry” crabs at the time but laughed out loud when our dive guide gingerly tipped the box over to reveal a small crab clinging to the squared off edge. As soon as the box was released, it wobbled off, under crab power, into the darkness.

Carry crab w:banana Ned DeLoach
If you can’t find an urchin, carry a banana peel

While we’ve been mighty amused at the sight of a moving banana peel or a tipsy nudibranch, this is serious business to these crabs that depend on camouflage to avoid predators. We usually see them moving about at night so I wonder how many animals or pieces of debris we’ve passed by during the day that were serving as cover for one of these crabs?

Carry crab w:jellyfish Ned DeLoach
Carry Crab (Ethusa sp.) carrying an upside-down jellyfish (Cassiopea sp.) for shelter

Two of my favorite sightings are a tiny crab that was totally overpowered by the jellyfish it was carrying – begging the question of who was carrying whom and the other was the crab at the beginning of this post, that had pulled a sea pen, a soft coral of the order Pennatulacea, from the bottom. Sea Pens are sessile animals that anchor themselves into the substrate with a fleshy peduncle. I knew something was amiss when I saw the entire animal exposed and lying on its side in the open sand. I paused and watched for about a minute and sure enough it started walking sideways – imagine that!