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