Trilobite Classification - The Nine Orders of Trilobites

Phylum Arthropoda

Page within:
Tree of Life
Of related interest:
Paleozoic Paleobiology
Trilobite Paleobiology
Trilobite Evolutionary Arms Race
Numerous fossil image galleries

cephalon front part (head) of the trilobite
isopygous pygidium and cephalon of essentially equal size
macropygous pygidium larger than cephalon
micropygous pygidium is much smaller than cephalon
pygidium rearmost body section (tagma) comprising fused segments, including tail that is separated from thoracic segments by an articulation
schizochroal a type of trilobite eye with compound lenses, each with separate cornea, and each lens separated from others by deep scleral walls. A corneal membrane extends downward into sclera. (contrast with see abathochroal and holochroal trilobite eye types).
spinose having an exoskeleton with one to many spines
subisopygous pygidium somewhat smaller (subequal) to cephalon
suture A linear break in the trilobite's exoskeleton along which it separated during molting

Fortey RA 1990. Ontogeny, hypostome attachment and trilobite classification. Palaeontology 33:529-576.
Fortey RA. 2000. Trilobite! Eyewitness to Evolution. HarperCollins, London.
Fortey RA A. 2001. Trilobite systematics: The last 75 years. Journal of Paleontology 75:1141–1151.
Kaesler RL, ed. 1997. Treatise on Invertebrate Paleontology, Part O, Volume 1, revised, Trilobita. Geological Society of America and University of Kansas Press, Lawrence, Kansas.
Levi-Setti R 1993. Trilobites. University of Chicago Press, Chicago.

A Guide to the Orders of Trilobites
- website by Dr. Sam Gon III