can anyone help id the part 2

[alvintheclownfish]

ok this guy live where its covered in corraline algae on the rock where my polyps are, it looks like the red patch lifts up like a sewr grate and he sticks his tentacles out, looks marbled color, black n whit, sticks out then when disturbed goes right back in anyonE?



just look carefully youll see it

 

[Anonymous]

I can't make out your picture. From your description, it sounds like a worm but I'm not sure.