Here is the full list of all 32 Another Crab's Treasure achievements worth 1,000 gamerscore.
Defeated Nephro.
Defeated the Polluted Platoon Pathfinder.
Defeated The Duchess.
Defeated the Royal Shellsplitter.
Defeated the Curdled Carbonara Connoisseur.
Defeated Heikea.
Defeated Topoda.
Defeated the Ceviche Sisters.
Defeated the Scuttling Sludge Steamroller.
Defeated The Consortium.
Defeated the Diseased Lichenthrope.
Defeated Pagurus.
Defeated Voltai.
Defeated Roland.
Defeated Petroch.
Defeated Inkerton.
Defeated Camtscha.
Defeated Camtscha (For real.)
Defeated Praya Dubia.
Defeated Firth.
Get your shell back.
Completed the Path of the Predator.
Completed the Path of the True Crab.
Completed the Path of the Hermit.
Begin the treasure hunt.
Upgrade your fork to its full potential.
Buy some shell insurance.
Fall to your death for the first time.
Find a certain hero's helmet.
Shoot a crab with a gun.
Try on every shell in the game.
Learn all Adaptations.