I'd say the crap is probably from the crab. He must have eaten something prior to you putting him in that cup. I hear crabs have a fast moving digestive track, which is what leads me to this conclusion.
Looks like a rock crab that come in live rock very very tiny and grow to get quite big. Move around rock three times thier size and will eat what ever it can catch. Catches alot of things! Notice the very pointed pincher. Tearing, ripping, poking and digging.
last night i actually found another crab clinging onto a rock. so i decided to grab him. guess i grabbed him too hard because i ripped him in two oops. either way ill probably flush these crabs down the toilet..
what do you guys think about green emeralds though?
I'd say the crap is probably from the crab. He must have eaten something prior to you putting him in that cup. I hear crabs have a fast moving digestive track, which is what leads me to this conclusion.
I'm thinking mythrax also. If you look at the ends of it claws, they should look like little "scoopers" on the inside part; they use it for scraping the rock clean. I've had some that seemed (were) harmless for a long time, then they hit a certain size (in my case, always much bigger than that guy) and start displaying what can only be described as predatory ambush tactics.