n large amphibious animal swarm 

Perception +11; darkvision, tremorsense (imprecise) 15 feet

Skills Athletics +12

Str +4 Dex +2 Con +3 Int -4 Wis +1 Cha -1

AC  19; Fort +13, Ref +10, Will +7

HP 42; Immunities precision, swarm mind; Weaknesses area damage 5, splash damage 5

Speed 30 feet, swim 15 feet

Swarming Snips [>] Each enemy in the swarm's space takes 2d8 piercing damage (DC 20 basic Reflex save). Creatures that fail this save also take 1d4 persistent bleed damage.

Bestiary 3, page 58.