Trilobites are an entirely extinct class of arthropods. Trilobites were a very diverse group consisting of 9 orders and numerous families, with over 15,000 recognized species! Though often considered primitive, they had a number of advanced features such as compound eyes, antennas and cerci.

Trilobites were found in nearly every marine habitat from the deep ocean floor to the near shore envrionment. Some may have occupied the intertidal zone, and may have occasionally washed up on the beach, but none are known to have occupied land or freshwater habitats.

Trilobites ranged in size from less than 1 mm to over 2½ feet!

Trilobites had a gradual metamorphosis, typically adding only 1 segment with each molt until they reached the adult form and number of segments. The first stage is called the Protaspid, the middle stages the Meraspid and the adult form is called the Holaspid. Usually only the hardened calcified parts fossilized so any newly hatched stages that lacked a calcified shell would be unknown to us.

Considering that they have been extinct since the end of the Permian , it is amazing how much we know about them!

For more information on trilobites, see the definitive guide to the trilobites.

The group of trilobites shown here is what is known as a "growth series". These are all holaspids, showing that, like lobsters, trilobites continued to grow once they reached the adult form.

These Trilobites are of the most common and best known trilobite species, Elrathia kingi in the order PTYCHOPARIIDA.

The trilobites in this group range from 16.2mm to 39.8mm in length and are referred to by number, #1 being the smallest and #5 being the largest.

Below you'll find links to pages showing closeups and meausrements of each trilobite specimen. #2 and #5 also show ventral views.