Identify the fossil, describe its key features, state its pygidium size relative to its cephalon, explain the functions of parts X and Y, and specify its geological period.

a) Identification:
The fossil is a Trilobite.

b) Describe the fossil:
Trilobites are extinct marine arthropods characterized by a segmented body divided into three longitudinal lobes (an axial lobe and two pleural lobes) and three transverse sections: a head region (cephalon), a segmented middle region (thorax), and a tail section (pygidium). They possessed a hard exoskeleton and compound eyes.

c) State the size of the pygidium in relation to the cephalon:
The pygidium is approximately the same size as or slightly smaller than the cephalon.

d) What are the functions of the parts labelled X and Y?
Function of X: Protection of internal organs and articulation for movement.
Function of Y: Vision.

e) State the Period during which the fossil lived:
The fossil lived during the Paleozoic Era (from the Cambrian to the Permian period).