The barreleye is a small deep-sea fish, measuring about 6 inches (15 cm) long. Its most striking feature is its transparent head, which allows you to see the fish's internal structures ...

The footage, captured in Spain's Canary Islands, shows the female fish, whose Latin name translates to "black sea monster," swimming through the light-filled ocean waters off the coast of Tenerife.

Weedy sea dragons have very long, thin snouts; slender trunks covered in bony rings; and thin tails which, unlike their seahorse cousins, cannot be used for gripping. They have small, transparent ...

To move, this species uses two fins—one pectoral and one dorsal—that are so thin they are almost transparent. As with sea horses, sea dragon males are responsible for childbearing. But instead ...