Dermal denticles are small, hard, tooth-like structures, also called placoid scales. They have the same structure as a tooth, having an outer layer of enamel, dentine and a central pulp cavity. Sharks' teeth and skin are composed of this type of scale. Dorsal Fin - This is the fin that is located along the fishes back. Exoskeleton - An exoskeleton is a tough, structural body armor made of chitin.
Crustacean s have exoskeletons.
Gill - Breathing organ in fish. Gut - The intestines of a fish. Hermaphrodite - Having the organs of both sexes. Invertebrates - Animals without backbones. This can include corals, snails, and shrimp or crabs.