- Axis - the central lobe of the trilobite exoskeleton. This
together with the two lateral or pleural lobes gives rise to the name trilobite.
- Cephalon - the 'head' of the trilobite.
- Cranidium - consists of the glabella and the free cheeks.
- Doublure - where the exoskeleton folds under the lower side of the trilobite.
- Facial sutures - separate the fixed and free cheeks. Used to assist in moulting but not present in all trilobites.
- Fixed cheeks - areas of the cephalon between the glabella and the facial sutures.
- Free cheeks - areas of the cephalon outside the facial sutures.
- Glabella - bulbous structure in the axial area of the cephalon. Contained the trilobites stomach.
- Graptolites - planktic colonial organisms alive at the same time as the trilobites but died out millions of years before them.
- Hypostome - plate on the ventral side of the animal, below
the glabella. The trilobites mouth was located at the posterior end of
- Pelagic - animals capable of swimming through the open ocean.
- Planktonic - anything that drifts through the open ocean.
- Pygidium - the 'tail' of the trilobite. Also known as the protopygidium in protaspids (early growth stages).
- Rostral plate - a small plate between the doublures of the free cheeks.
- Sister groups - nearest evolutionary relatives.
Author: Laurence Dale
Last updated: 18/11/06
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produced by students
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Palaeobiology programme in the Department
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