Beast of the Week: Scylla

Two of the most memorable monsters of Greek Mythology never (to my knowledge) made the transition to D&D.  Scylla and Charybdis, the twin terrors of the Straits of Messina.  This week you get Scylla, next week Charybdis.  So without further ado, here she is:

Scylla*
AC: 0 (20)
HD: 7*
Move: 60 (20) Swim 120 (40)
Attacks: 6 bites
Damage: 1d10 each
No. Appearing: 1 (1)
Save As: F7
Morale: 10
Treasure Type: D
Alignment: Chaotic
XP: 850

Scyllas are 50' long serpentine water monsters with the torso of a woman and six canine heads atop long, flexible necks that grow from where the humanoid torso meets the snake-like body.  They live in sea cliff caves, and prefer narrow straights where ships are likely to pass close to their lairs.  When a ship passes too close, the Scylla will strike out with its five canine heads, each seeking to bite and grab a sailor from the ship.  They rarely break off an attack until each head has a victim, but once it has taken six victims, it withdraws and returns to its lair to feast.  Scyllas are only damaged by spells or magic weapons.