Crayfish, Giant (CR 3)

Large Vermin (Aquatic)
Alignment: Always Neutral
Initiative: +2 (Dex); Senses: darkvision 60 ft.

AC: 16 (+9 natural, -2 Dex, -1 size), touch 6, flat-footed 16
Hit Dice: 4d8+12 (30 hp)
Fort +7, Ref -1, Will +2
Speed: 20 ft., swim 30 ft.
Space: 10 ft./5 ft.
Base Attack +3; Grapple +11
Attack: claw +7 melee
Full Attack: 2 claws +7 melee
Damage: Claws 1d6+5
Special Attacks/Actions: -
Abilities: Str 20, Dex 7, Con 16, Int -, Wis 12, Cha 1
Special Qualities: Amphibious, vermin traits
Feats: Improved Initiative; Run
Skills: Swim +13
Advancement: Large (5-8 HD), Huge (8-12 HD)
Climate/Terrain: Warm aquatic
Organization: Solitary
Treasure/Possessions: None

Source: Dragon #321

Giant crayfish hide until prey comes near, and then leap out attempting to gain surprise.

These strange creatures are found only in fresh water. They move slowly when walking, but they can swim with great rapidity for short periods.

Aquatic Subtype

Creatures with the aquatic subtype always have swim speeds and thus can move in water without making Swim checks. An aquatic creature can breathe underwater. It cannot also breathe air unless it has the amphibious special quality.