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