I haven't found an exact precedent. Here are some similar abilities...
Drown (Ex): The first victim hit by a dhour's pseudopods must make an opposed grapple check with the dhour. If the dhour wins the check, it draws the victim into its fluid body. The victim takes 2d6+6 points points of acid damage per round, and is also at risk of drowning (see Water Dangers in the Dungeon Master's Guide for the risks and effects of drowning). Because a dhour is composed of protoplasm, spells such as water breathing offer no help in surviving the effect of drowning in their fluids.
A trapped victim can attack the dhour or make additional grapple checks to escape its grasp. The character cannot cast spells with a verbal component or use any other item or ability that requires speech. If other characters use slashing or piercing weapons to attack a dhour while it is holding a victim, those attacks have a 25% chance of hitting the trapped character, and they do no harm to the dhour.
While holding a victim, a dhour continues to attack with its pseudopod, dealing slam damage to other characters. A dhour cannot move while holding a victim.
Drown (Ex): To use this ability, a breathweird must hit an opponent of Medium size or smaller with its slam 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 draws the victim into its fluid body. The victim is at risk of drowning (see Water Dangers in the DMG for the risks and effects of drowning). A trapped victim can attack the breathweird or make additional grapple checks to escape its grasp. The character cannot cast spells with a verbal component or use any other item or ability that requires speech. If other characters use slashing or piercing weapons to attack the breathweird while it is holding a victim, those attacks have a 25% chance of hitting the trapped character, and they do no harm to the breathweird. While holding a victim, the breathweird continues to attack with its pseudopods, dealing slam damage to other characters. Breathweirds have a +12 racial bonus on grapple checks (already figured into the Base Attack/Grapple entry above).
Drown: The first victim hit by an aballin's pseudopods must make an opposed grapple check with the aballin (the monster's bonus on this check is +11). If the aballin wins this check, it draws the victim into its fluid body. The victim is at risk of drowning (see Water Dangers in the DMG for the risks and effects of drowning). Because the aballin is composed of acid, not water, spells such as water breathing offer no help in surviving the effect of drowning in their fluids.
A trapped victim can attack the aballin or make additional grapple checks to escape its grasp. The character cannot cast spells with a verbal component or use any other item or ability that requires speech. If other characters use edged weapons to attack the aballin while it is holding a victim, those attacks have a 25% chance of hitting the trapped character, and they do no harm to the aballin.
While holding a victim, the aballin continues to attack with its pseudopods, dealing slam damage to other characters.