n large amphibious animal 

Perception +13; darkvision, tremorsense (imprecise) 15 feet

Skills Acrobatics +9, Athletics +15, Stealth +9

Str +6 Dex +2 Con +4 Int -4 Wis +2 Cha +0

AC  21; Fort +15, Ref +9, Will +9

HP 114; Weaknesses bludgeoning 5

Protective Pinch [R] Trigger A creature adjacent to the hermit crab attempts to Strike the hermit crab while it is Retracted; Effect The hermit crab makes a big claw Strike against the triggering creature.

Speed 20 feet, climb 10 feet, swim 15 feet

Melee [>] big claw +15, Damage 2d8+8 piercing plus Grab

Melee [>] claw +15 (agile), Damage 2d4+8 piercing

Constrict [>] 1d8+6 bludgeoning, DC 22

Retract [>] The hermit crab curls fully into its shell to protect itself. This gives it a +4 circumstance bonus to AC, removes its weakness to bludgeoning damage, and grants it resistance 5 to piercing and slashing damage. The only actions the hermit crab can use while in this state are Protective Pinch and Interact to come out of its shell.

Bestiary 3, page 58.