Lets see what I can come up with.
Pic 1, the most common ones have a hard shell usually divided into 8 sections. They feed on algae amongst other things and bore holes in rocks. This one is unlike most if not all that I'm familiar with. It doesn't have 8 distinctive sections and is around 5"-6" long and I've seen it stretch close to 10".
Pic 2, the name of this goes well on a salad but if aggravated in a reef tank could be poisonous. It spends most of it's time on the sandbed.
Pic 4, Fairly common hitchhiker from Tonga. Looks completely different at times with a smooth, glossy hard surface. Common name begins with same letter as it's Family name. Diet can vary between different ones, omnivore, scavanger, or specific predator.
