Trilobites are an important group of extinct arthropods. Their bodies were divided into three segments: the head, body and tail. Although they looked like woodlice, and could roll into balls for protection, trilobites were more closely related to spiders and scorpions.
The majority of trilobites lived on the sea floor, though some could swim. Some large trilobites were active hunters, feeding on smaller, soft-bodied invertebrates.
Trilobites became extinct 250 million years ago, but even so survived for over half of the history of animal life. This first 250 million years of animal life is known as the Palaeozoic era.