Its hard to tell, but from that photo it looks like a limpet. Many limpets are intertidal, spending much, sometimes most, of their day out of the water. Leave it alone......it will go back in when it needs water. Limpets are unlikely to carpet surf, but other intertidal snails like periwinkles will frequently end up outside the tank. However, their operculum seals in moisture, so they can survive a very long time out of water. Limpets don't have an operculum, so they never move very far from water.