Name: Trinucleus.
Meaning : Three nuclei, three centres.
Grouping: Arthropod, Trilobite.
Informal ID: Trilobite.
Fossil size: Head-tail length 2cm/ 1/3 in.
Reconstructed size: As above.
Habitat: Muddy deep sea floor.
Time span: Middle to Late Ordovician, 470-440 million years ago.
Main fossil sites : Western Europe, North Africa.
Occurrence: •