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