Here is the full list of all 32 Another Crab's Treasure achievements.
Get your shell back.
Defeated Firth.
Try on every shell in the game.
Defeated the Curdled Carbonara Connoisseur.
Shoot a crab with a gun.
Defeated Praya Dubia.
Defeated Camtscha.
Defeated Camtscha (For real.)
Find a certain hero's helmet.
Fully upgrade Kril's fork.
Defeated Inkerton.
Defeated Petroch.
Learn all adaptations.
Defeated Roland.
Defeated Voltai.
Unlock all skills on the Path of The True Crab.
Unlock all skills on the Path of The Predator.
Unlock all skills on the Path of The Hermit.
Defeated the Ceviche Sisters.
Defeated the Scuttling Sludge Steamroller.
Defeated the Consortium.
Defeated Pagurus.
Defeated Topoda.
Defeated Heikea.
Defeated the Diseased Lichenthrope.
Start the treasure hunt.
Purchase some insurance.
Fall off a cliff.
Defeated Magista.
Defeated a miniboss.
Defeated the Royal Shellsplitter.
Defeated Nephro.