Worm / Cucumber ID?

[falconut]

Does anybody know what this thing is? It's about 1/2" long & I pulled it out from under a rock next to my dead serpent star? It has tentacles and is moving along the bottom of the cup. Here is a photo:

 

[Mike J.]

Definitely a sea cucumber. Don't know what kind, sorry. I'd keep it though.

 

[falconut]

Alright, I threw it in my refuge.