When beachcombing around tide pools, you’re likely to find a rather prehistoric-looking creature stuck to the side of rocks. They’re practically impossible to remove from their chosen spots; neither human hands nor the crashing waves have an easy time of it. These are the West Indian Chitons, locally called “Suck Rocks” for obvious reasons.

Suck Rocks are a type of snail. They can grow up to three inches in size and have overlapping plates and a dark body underneath. The dorsal shell is an oval, convex form with horizontal lines revealing the overlapping eight plates which make up the shells and which inspired another name, coat-of-mail shells. Around the plates are narrow, leathery borders, girdles, which are covered with tiny spikes. These allow them to stick so strongly to the rocks. The plates also provide protection and the ability to arch up and move across uneven surfaces, though you’ll likely never notice any movement at all; their movement across the rocks is so gradual that it’s imperceptible.

Chitons are most visible when the tide is lowish because they live in the intertidal zone. They spend their days meticulously grazing algae from rocks, eating with tongue-like ribbons of tiny teeth with metal tips. They also scrape algae off each other’s backs.

Just below its shell, Chitons have thousands of eyes and though more extensive research is required, it has been discovered that they can differentiate between a predator’s shadow and changes in light caused by clouds. Their predators include sea stars, crabs, sea snails, birds, and fish.