Horned helmet shell

Cassis cornuta

Guardian Matt Quintal

So if you were a sea urchin this creature would be the stuff of nightmares. With a massive foot it would be too fast to outrun and when close enough, it rises up and falls upon you. It has a paralysing liquid which will hold all of your spines still, and helpless, motionless, you will feel the monsters extendable mouth melt a hole through your shell and then move into you to devour your insides.