The is the Antillean Sponge Crab, (Cryptodromia antillensis). This nocturnal crab relies on camouflage to survive. They are usually wearing a sponge on their head, but this particular crab is naked. You can see the fine hairs on her exoskeleton.
The Spotted Porcelain crab will consume bits of food that are in your water column, capturing them with their webbed appendages that they wave throughout the day. An attractive reef safe crab often found in groups, and will love host anemones.
Eats Diatoms, Algae and Detritus on the rocks and glass in your tank. Extremely hardy under normal water conditions. This smaller snail only grows to about 2/5-3/5 of an inch.