Anomalocaris

This three-foot creature glides forward on rippling oar-like lobes, spiked appendages waving menacingly from either side of its round mouth

Originally Posted by Jonah Bomgaars  
On the d20despot.blogspot 

Anomalocaris        

CR 1XP 400 N Small vermin (aquatic)Init +1; Senses darkvision 60 ft.; Perception +1

DEFENSE

AC 13, touch 12, flat-footed 12 (+1 Dex, +1 size, +1 natural)

hp 13 (2d8+4)Fort +5, Ref +1, Will +1Immune mind affecting effects

OFFENSE

Speed 5 ft., Swim 30 ft. Melee bite +2 (1d6 plus grab)

Special Attacks gnaw (1d6)

STATISTICS

Str 11, Dex 12, Con 14, Int –, Wis 13, Cha 2

Base Atk +1; CMB +1 (+3 grapple); CMD 12

SPECIAL ABILITIES

Gnaw (Ex)An anomalocaris gnaws at its prey, dealing bite damage, when it makes a successful grapple check (including the one made as part of a grab with its bite attack). 

ECOLOGY

Environment any oceans

Organization solitary

Treasure none

Anomalocaris is a predator of primeval seas.  Its three-foot-long, segmented body is broadened by a lateral array of a dozen paddle-like lobes; these grow longer toward the creature’s midsection, giving it an oval or diamond-shaped outline.  These lobes, along with a tail resembling that of a shrimp, propel it through the water with an undulating motion.  Its rounded head is topped with two large compound eyes on short stalks.  A circular mouth of overlapping, serrated plates occupies the underside of the head.  The anomalocaris has two six-inch-long barbed claw-like appendages that it uses to graps prey and pull it towards its grinding mouth.