These sea monsters grew upwards of 40 feet (12 meters) long. About half that length was neck, a feature that allowed Styxosaurus to sneak up on schools of fish as it slowly cruised the shallow ...

Xiphactinus was one of the largest bony fish of the Late Cretaceous and is considered one of the fiercest creatures in the sea. A powerful ... long (5-meter-long) monster through the surface ...

The short-necked plesiosaur likely had few enemies, but those that attacked were some of the fiercest monsters of the seas, including sharks with razor-sharp teeth and the giant mosasaur Tylosaurus.

The ornately colored sea anemone (uh-NEM-uh-nee) is named after the equally flashy terrestrial anemone flower. A close relative of coral and jellyfish, anemones are stinging polyps that spend most ...

Sea dragons are some of the most ornately camouflaged creatures on the planet. Adorned with gossamer, leaf-shaped appendages over their entire bodies, they are perfectly outfitted to blend in with ...

This story appears in the October 2017 issue of National Geographic magazine. How close can you really get to two monster squid fighting? Very close, it turns out. This month National Geographic ...

The green turtle is a large, weighty sea turtle with a wide, smooth carapace, or shell. It inhabits tropical and subtropical coastal waters around the world and has been observed clambering onto ...

Sea moss is rich in nutrients—but it can also contain dangerous levels of heavy metals and iodine. Here’s what to know before you take it. A mix of kelp, Irish moss, and sea lettuce harvested ...

Females likely migrated hundreds of miles to lay eggs on sandy beaches, much like sea turtles do today. Movement onshore, however, was difficult. An adult female Protostega may have weighed a ton ...

Our earthly insignificance and In 2010, National Geographic celebrated the 25th anniversary of Explorer, the longest-running documentary series in cable television history. Monsters and Critics ...