The body of a mature purple worm is 5 feet in diameter and 80 feet long, weighing about 40,000 pounds. The creature has a poisonous stinger in its tail.

In battle, a purple worm forms into a coil 20 feet in diameter, biting and stinging anything within reach.
Improved Grab (Ex): To use this ability, a purple worm must hit with its bite attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it establishes a hold and can attempt to swallow the foe the following round.
Poison (Ex): Injury, Fortitude DC 25, initial damage 1d6 Str, secondary damage 2d6 Str. The save DC is Consitution-based.
Swallow Whole (Ex): A purple worm can try to swallow a grabbed opponent of a smaller size than itself by making a successful grapple check. Once inside, the opponent takes 2d8+12 points of crushing damage plus 8 points of acid damage per round from the worm?s gizzard. A swallowed creature can cut its way out by using a light slashing or piercing weapon to deal 25 points of damage to the gizzard (AC 17). Once the creature exits, muscular action closes the hole; another swallowed opponent must cut its own way out. A Gargantuan worm?s interior can hold 2 Large, 8 Medium, 32 Small, 128 Tiny, or 512 Diminutive or smaller opponents.
Skills: A purple worm 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.

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System Reference Document -> List of Creatures (SRD)