Do Mithrax crabs have fan/feather like appendages?

[William Sharkspeare]

I know I have a large Ruby Mithrax that came with my TBS rock, but occasionally I will see some mobile invert that is filtering the water column. I also think it has some long skinny antennae. Unfortunately I can never get a good look at it. Is it the crab or some kind of shrimp? Attached is a picture of my crab. I don't believe this is what I am seeing.

 

[nautical_nathaniel]

Possibly a barnacle, they reach out and wave their fan through the water:

 

[Justfebreezeit]

Sounds like a porcelain crab or similar

 

[keagan]

There's a ton of barnacle shells all over that rock so I second barnacle

 

[William Sharkspeare]

Not a sessile invert. This thing definitely moves around.

 

[Justfebreezeit]

 

[keagan]

Where it's Florida rock it could be a mole crab (Emerita talpoida) or a green porcelain crab (Petrolisthes armatus) justfebreezeit is likely right IMO. Mole crabs are intertidal so more likely the porcelain crab if they don't leave the rock near the beach before collection or something.

 

[William Sharkspeare]

Definitely a porcelain crab. Thanks.

 

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TBS Hitchhikers - Porcelain Crab