Nautilus

The Nautilus is a passive mob added by Upgrade Aquatic. They are found in underwater caves and ravines.

Behavior
Nautiluses bob up and down and dash randomly, leaving a bubble trail when they do. When approached by a player, Drowned, or Squid, or if they are hit they will perform a few dashes to escape. Additionally, Nautiluses are immune to bubble columns and are unaffected by their pull. Nautiluses released from a Bucket will not despawn.

Drops
The Nautilus always drops one Nautilus Shell and can be captured in a Bucket.