Leech, Giant (CR 1/3)

Small Vermin (Aquatic)
Alignment: Always neutral
Initiative: +1 (Dex); Senses: blindsight 10 ft. and scent

AC: 12 (+1 size, +1 Dex), touch 12, flat-footed 11
Hit Dice: 1d8 (4 hp)
Fort +2, Ref +1, Will -1
Speed: Swim 10 ft.
Space: 5 ft./5 ft.
Base Attack +0; Grapple -6
Attack: Bite +2 melee
Full Attack: Bite +2 melee
Damage: Bite 1 plus blood drain
Special Attacks/Actions: Anesthetize, attach, blood drain, disease
Abilities: Str 6, Dex 12, Con 11, Int -, Wis 8, Cha 2
Special Qualities: Vermin traits
Feats: Weapon Finesse
Skills: Hide +9 and Swim +6
Advancement: 2-3 HD (Small)
Climate/Terrain: Warm marsh
Organization: Colony (2-5) or swarm (6-11)
Treasure: None

Source: Stormwrack

This worm like creature is the size of a human forearm. Its mouth is a round, suckerlike orifice.

Giant leeches have little ability to attack foes in open water or clear terrain but can pose a serious danger to characters wading or swimming in murky or muddy water.

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.