Like mentioned before in chapter TRILOBITA, trilobites had an repeating ecdysis
(moulting) during the body growth phases from larval stage to adult trilobite.
During moulting process, the facial sutures (Suturae) representing the breaking
points between cranidium (glabella+ fixigenae) and librigenae including
conjunctive structures. The course of sutures continuing, passing over the doublure, at cephalons ventral side, cause moulting is only possible in common
interaction with hypostome and rostral plate. Furthermore sutures are one of the
key factors in classification of trilobites groups.
The definition of a suture is defined by it's position at cephalons edge
relative to the genal angle. There are three main types of facial sutures
distinguished as followed:
Proparian sutures are anterior advancing the genal angle. The gonatoparian type
is ending at the genal angle (travelling). Finally the opisthoparian suture are
ending at the posterior cephalons edge (lagging).
These courses are described at the cephalon of our Zlichovaspis sp. (dorsal
view) using the punctated lines. Of course every species has it's own one
characteristic type of facial sutures. Zlichovaspis sp. has proparian