Trilobites are an extinct form of Arthropod most closely related to modern horseshoe crabs.
They lived from the Cambrian Period to the end of the Permian. They are divided vertically into 3 distinct “lobes” hence the name tri-lob-ite.
They are the Central or axial lobe and the two pleural lobes on either side. They are further divided into 3 sections.
They are the Cephalon or head section, the Thorax or body section and the pygidium or tail section.
The head and tail are solid exoskeleton shields but the thorax is segmented and allows the trilobites to “enroll” for protection from danger.
The ventral or underside of the creature contained the soft tissues, legs, gill branches and mouth or hypostome.
In some parts of the world these soft tissues are found preserved but normally all that is preserved is the exoskeleton.