Answer
Trilobites are members of the extinct Arthropoda subphylum, Trilobata. Their origin was probably in the preCambrian, and they were abundant in the Cambrian and Ordovician periods. They were marine bottom living creatures, but they probably could swim. They obtained nourishment mainly as scavengers, but they were also predators and filter feeders. Trilobites became extinct about 200 million years ago.
Work Step by Step
Trilobites had a hard exoskeleton, but it was segmented; therefore, they could roll themselves into balls. To facilitate growth the exoskeleton was periodically shed by a process known as molting or ecdysis.
From head to tail, the trilobite body was divided into three tagmata--head, thorax and tail. They were also characterized by three body lobes, from side to side--one central (axial) and two pleural (side)lobes.
The head, or cephalon, bore eyes, mouthparts, and antennae; the thorax was composed of many joined segments, and the tail (pygidium) comprised many fused segments.
Trilobites constitute a very important group of early fossils.
