The Clamavore!

CLAMAVORE

SIZE: Large (8-10 ft. wide)
MOVE: 180 ft., swimming 180 ft.
ARMOR CLASS: 0
HIT DICE: 8
ATTACKS: 2
DAMAGE: 2-12 + 6
SPECIAL ATTACKS: Spit pearls
SPECIAL DEFENSES: Half damage from fire
MAGIC RESISTANCE: None
RARITY: Very rare
NO. ENCOUNTERED: 1-4
LAIR PROBABILITY: 80%
TREASURE: None
INTELLIGENCE: Animal
ALIGNMENT: Neutral
LEVEL/X.P.: 6 / 1,100 + 10/hp

General information: Clamavores are an abomination from the Elemental Plane of Water. None know what purpose brings these horrors to the Prime Material Plane, but one thing is certain: when on the Prime Material Plane they seek to destroy all mundane life.  A Clamavore will always attack whichever opponent which has done the most damage to it previously. It attacks with the 2 claws. Should a claw strike an opponent, rearward facing spikes will embed itself in the target. In subsequent rounds, the Clamavore will work the claws back and forth in a saw-like fashion, automatically doing damage to the ensnared victim. Should an unfortunate individual be struck by both claws, the Clamavore will attempt to bite with its shell for an additional 2-12 +6 damage.

Additionally, the Clamavore can spit one pearl per round up to 120 ft. Upon a hit, the pearls do 2-12 damage, destroy any metal it contacts (magic items saves versus acid), and drains one point of Wisdom from the victim (save to negate). If the opponent is in the grasp of both claws, the Clamavore can forgo the bite attack and spit a pearl at +4 to hit. A Clamavore will have 3-6 pearls available for spitting, which are replaced at a rate of 1 per week.

Physical description: At rest, Clamavores appear to be enormous clams (8-10 feet across). They have peculiar markings all over the shell consisting of a circle with two lines radiating outward forming a V shape, terminating in smaller circles. When the Clamavore takes notice of a mundane lifeform, the true, horrifying nature of the creature becomes apparent. The shell opens, the hinge at the base separates, and 6 limbs sprout forth, 4 clawed, chiton encrusted legs, and two likewise encrusted arms, each terminating in terrible, snapping claws.