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