The image above provides most of the dorsal morphological terms used
to define trilobite species, genera, families, and orders. Ventral (underside) morphology can also be
important. For example, there are hypostomal attachment
terms describing the way the hypostome (a hard mouthpart on the underside
of a trilobite) attaches to the rest of the cephalon. There are also broader
categories (Major Trilobite Features),
that refer to major body divisions such as cephalon, pygidium,
cranidium, axis, etc. There are some terms that relate
to the relative sizes of the cephalon and pygidium.
Facial sutures (lines along which
the exoskeleton split to allow molting) are also important in classifying
trilobites. There was also significant variation of trilobite eyes. We don't know very
much about a trilobite's internal anatomy, with some exceptions!
Finally there are some special morphological
terms that apply only to certain groups of trilobites. If
you want more detailed definitions of the terms in the image above,
I have provided a general alphabetical glossary
of terms.
