wired crab

anyone know what kind of crab this is??

Dorippe frascone carrying Astropyga radiata. Apparently it's a very common association.

Astropyga radiata = emperor sea urchin?

Called the long-spine or blue-spotted urchin. It's the one with 5 rows of bright blue spots between the long spines and is found on muck bottoms.

is the crab a specific crab ? or do they attach to any crabs ? and do or can any urchins do this ?

it's the other way around, Giles. This species of crab (and others like it) carry around objects for protection. The last 1 or 2 pairs of legs point upwards over the back so they can grip onto their "armor". I've seen several pictures from Indonesia of tDorippe carrying Astropyga. I don't know if the crabs actually prefer Astropyga or if it's just that they both live in the same muck environment.

perfect now i know the name of it

just a very fun looking crab whit the sea urchin on top of it

so the urchin has no choice in the matter or does it like it .. does the urchin get any benefits from it .. i cant imagine it wants to be a living shield .. especially when the crab is made with its own armour !!

Giles,

I'm sure, like the body guard I hired back in elementary school, the urchin gets a free lunch out of it.

You were a better employer than the crab since the urchin certainly can't feed while it's being carried around. I don't think the urchin gets any benefit. A quick web search produced images of Dorippes carrying around other species of urchins, sand dollars, and shell fragments. This image clearly shows the small hind legs curled around the edge of a sand dollar http://www010.upp.so-net.ne.jp/uca/crab/cr...x/crab0108.html

A fish that eats crabs might not bother to attack an urchin; same for octopus who love crab meat. Maybe they're not used as armor but rather for camoflague.