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