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