Placoid scales are tiny, hard, tooth-like structures, also called dermal denticles. 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 placoid scales.

The dorsal ridge is a raised line or hump on the back of a some whales (instead of a dorsal fin).

Poikilotherms are animals whose internal temperature changes depending on the environment. Reptiles are poikilothermic.

The snout is the front part of an animal's face.

Ray-finned fish (class Actinopterygii) are the largest group of fish. These bony fish evolved during the very end of the Silurian, about 408 million years ago. These fish dominate the seas today. Sharks are not ray-finned fish.

Benthic feeders are organisms (plants and animals) that live in or on the bottom of a body of water. Some sharks, like angel sharks

A calf is a baby whale (or other baby cetacean).

The calf shark (also known as the Bigeye sixgill shark and the Lesser sixgill shark) lives in warm temperate seas, usually living on the bottom. It averages about 6 feet (1.8m) long. The skin ranges from dark gray to light gray. Classification: Order Hexanchiformes

Family Carcharinidae (also known as requiem sharks) are a type of large Carcharhiniformes sharks

The Carribean Reef Shark (Carcharhinus perezi