Use a hatchet or megatherium to harvest for max silica pearls and oil. Gives about a stack of chitin with a primitive metal hatchet and loads with the mega.

They seem to spawn in the south of the standard island map, usually near the water on a Sandy bitch at dusk and dawn

Trilobites... Also known as the Cockroach of the Sea!

If you spot one of these when 2x is active stop and kill it. High levels give 100 chitin, Oil, S pearls & B pearls.

You can find them on land next to an ocean & in shallow water. Where there's 1 their is usually a few more around aswell.