Another" what is this thing"?

[sharuq1]

Covered in a shroud of mucous, best pic I can get, it's about the size of an oversized pea with trailing lines of what I am assuming is mucous. Inside it looks like a curled up armadillo. That is to say I see spines, like on one of those pinecones with the triangular spines? It's roundish, it moves, no idea how it's moving, just moving over the rock. It isn't a jellyfish. It is more alike to a chitton, but round and shrouded in that mucous thing. Any clue? Just curious.