Coelacanth

Note: Make sure to name your coelacanth with a nametag. They will certainly despawn otherwise.

Coelacanth (meaning "Hollow Spine") is a large passive aquatic prehistoric creature that was added in Build 6.1. It is a living fossil fish that spawns naturally in the world but can also be created by the player.The only other naturally spawning creature is the nautilus. It is around 1 block tall and 3 blocks long and drops raw fish when killed. The three subspecies spawn randomly instead of in the biomes they are named after. The Ocean subspecies seems to be more common than the others. Right-clicking a coelacanth puts it into your inventory as an item.

BEHAVIOR
Coelacanth is an aquatic mob that can spawn naturally in the world. They tend to spawn in deeper waters, and sometimes in rivers and beaches. Most of the time, they gravitate towards the bottom of a pool. Since they are passive mobs and do not defend themselves, they are vulnerable to marine predators like mosasaurus and liopleurodon. They can only live underwater; when placed on land, they they flop around, dying of suffocation at a rate of one heart per second. Right-clicking catches them, and then you can release them into the water.

Like some other non-dinosaurian mobs, they cannot be tamed, ordered, fed, bred, or aged. They also do not make sounds.