The underwater world is full of fascinating and strange creatures. While we may be familiar with dolphins and sharks, there are thousands of lesser-known species that are equally amazing. Here are five such underwater creatures you've probably never heard of.

1. Vampire Squid (Vampyroteuthis infernalis)

Don't let the name fool you; the Vampire Squid doesn't feed on blood. This creature lives in the deep ocean and can turn itself inside out to avoid predators. Its name comes from its dark color and webbed arms, which resemble a cloak. Find out more about the Vampire Squid here.

2. Sarcastic Fringehead (Neoclinus blanchardi)

This aggressively territorial fish is found off the Pacific coast of North America. When threatened, it opens its large mouth in an attempt to fend off intruders. The fringe-like appendages over its eyes are what give this fish its unusual name. Discover more about the Sarcastic Fringehead here.

3. Leafy Seadragon (Phycodurus eques)

Resembling something out of a fairytale, the Leafy Seadragon is a type of seahorse found along the southern and western coasts of Australia. Its leaf-like protrusions provide camouflage among the seaweed and kelp formations where it resides. Learn more about the Leafy Seadragon here.

4. Dumbo Octopus (Grimpoteuthis)

Named for its resemblance to the cartoon elephant Dumbo, this deep-sea octopus uses ear-like fins to propel itself through the water. It lives at extreme depths of up to 7,000 meters and is known for its gentle nature. Find out more about the Dumbo Octopus here.

5. Christmas Tree Worm (Spirobranchus giganteus)

These colorful, festive-looking creatures are named for their tree-like appearance. They have beautiful, spiraling plumes that they use for feeding and respiration. Christmas Tree Worms are found on coral reefs around the world. Discover more about the Christmas Tree Worm here.