Corpsegrinder Worm

HD 8 AC chain Bite 2d6 + grab
Move 9 Burrow 3 Int 5 Mor 6

Barf 1/day
30' cone, 3d6 damage from bone shards (save for half) and covers targets in acid (1d6 damage each turn). One turn later, 1d6-5 animated skeletons rise from the barf and immediately attack.

Grind
Grabbed targets are hit automatically on subsequent turns for double damage.

Corpsegrinder worms are sluggish monsters about 40' long.  They have a mouth like a garbage disposal; when eating, they spit up almost as much as they swallow.

They frequent battlegrounds and graveyards, where they leisurely devour buried corpses.  They are scavengers first, and ambush predators second.  They will only attack if a person walks off alone, or if the PCs start messing with their food source (exhuming corpses, opening crypts).  If given a fresh corpse (or when they have grabbed someone), they will usually retreat with their prize and spend a couple of hours savoring it.

They will happily chase down and devour zombies.

It is usually apparent when you are in the territory of a corpsegrinder worm.  Buried coffins have been broken into and even sarcophagi appear well-gnawed.  When the dungeon is quiet, you can hear them behind the wall, regurgitating swallowed bones and grinding them in their mouths.  It sounds exactly like what you think it does.

Acid Rules: Take damage (usually 1d6) at the end of each of your turns.  Can be ended by pouring a liquid on yourself, scraping the acid off (1d6 damage), or removing your armor/clothing.

Shield Rules: Take no damage or effects of any kind from breath attacks if you make your save.