The Elasmosaurus is a large plesiosaur. It has a long, thin, slightly hooked neck, with a small head and tapered snout with small, narrowed black eyes. It has a plump body, thin, short flippers, and a short tail. It's a fisheater, not being built for hunting large prey.
The Subnautica Jellyray Elasmosaurus, more commonly known as "jellyfish" or "jellyray", bears a great resemblance to the Jellyray from Subnautica, hence the name. Its outer body, tentacles and tail are all a neon blue, while its inner body is a bright pink. You can see it under the surface of the water, just like the Aurora.
The Black Leviathan is a massive skin for the Elasmosaurus. The creature resembles a large Elasmosaurus, with black rocky armor. Running down the sides of the Leviathan are streaks of orange. The Black Leviathan's eyes and mouth are a deep orange color too. This skin is the largest aquatic creature in the game, and due to its size, it's actually hard to use when traveling in areas with many rocks and walls.
Elasmosaurus was a large plesiosaur species native to inland seas in the Late Cretaceous USA and various other locations. It was a sleek hunter, sticking the long neck through fish schools and snapping them.