Brine Swimmer (CR 3)

Large Vermin
Alignment: Always neutral
Initiative: +3 (Dex); Senses: low-light vision

AC: 17 (-1 size, +3 Dex, +5 natural), touch 12, flat-footed 14
Hit Dice: 5d8+10 (32 hp)
Fort +6, Ref +4, Will +1
Speed: 20 ft., swim 40 ft.
Space: 10 ft./5 ft.
Base Attack +3; Grapple +10
Attack: Bite +5 melee
Full Attack: Bite +5 melee
Damage: Bite 1d6+4
Special Attacks/Actions: Improved grab, rake 1d4+1
Abilities: Str 17, Dex 16, Con 15, Int -, Wis 10, Cha 4
Special Qualities: Immunity to acid and dehydration, snap turn, vermin traits
Feats: -
Skills: Swim +3
Advancement: 6-10 HD (Large); 11-15 HD (Huge)
Climate/Terrain: Warm aquatic
Organization: Solitary or colony (6-30)
Treasure/Possessions: None

Source: Sandstorm

Improved Grab (Ex): To use this ability, a brine swimmer must hit an opponent with its bite attack. It can then attempt to start a grapple as a free action without provoking attacks of opportunity. If it wins the grapple check, it establishes a hold and can rake.

Rake (Ex): Six legs, attack bonus +5 melee, damage 1d4+1.

Snap Turn (Ex): A brine swimmer can change direction quickly once each round as a free action. It can turn 180 degrees without expending any of its swim speed and can even use the run action after executing such a turn.

Skills: A brine swimmer has a +8 racial bonus on any Swim check to perform some special action or avoid a hazard. It can always choose to take 10 on a Swim check, even if distracted or endangered. It can use the run action while swimming, provided it swims in a straight line.

A brine swimmer grabs at prey with its mandibles, then holds on and rakes with its legs.

Brine swimmers can make sudden turns by flexing their segmented abdomens, and they use this surprising maneuverability both when hunting and when attempting to escape danger.

Brine swimmers generally travel in large groups, and a movement by one toward a food source soon brings dozens of others.