Cleon
Legend
Good, I think it's finally finished!
The working draft looks like a good start!
We can borrow this...
Light Fortification (Ex): A cacops' bony plates protect its vital areas and makes it resistant to extra damage from critical hits and sneak attacks. Anytime a cacops is hit by a critical hit or a sneak attack, it has a 25% chance to resist the extra damage.
I don't know BUGHUNTERS enough to comment on light vs somewhat-less-than-moderate fortification, so whichever. I agree with Shade that it doesn't need to change with size.
Everyone fighting the creature may well wind up in the water, no matter how the fight begins, as Anomalocaris is more than powerful enough to flip over a small boat, even one large enough to hold an entire infantry squad or typical AD&D adventuring party.