My Trilobites Trilobites are an extinct group of marine arthropods which existed during the Paleozoic era, from the Cambrian to the Permian period about 540-245 million years ago. In order to get bigger the trilobites periodically moulted, like all other arthropods.
Entire trilobites are uncommon because the skeleton breaks apart while moulting.
The trilobites have legs, located in pairs under each body segment. The extremities have also a fringed appendage probably with gill and swimming functions. Legs, antennae and other soft parts are rarely preserved. This Triarthrus eatoni from the North American strata of Beecher s Trilobite Bed have however both extremities and antennae fossilized. Many trilobites were capable of curling their body for protection.