Major subgroups in the Class

Trilobites come under the phylum Arthropoda. There are 9 orders, over 180 families, over 5000 genera and over 15000 species, with new species being described each year. There is far to much information to cover in this web site so I have provided details of the 9 orders and the associated suborders, superfamilies and families where appropriate. A more detailed description can be found at Sam Gon's web site, (See references).
    ORDER REDLICHIIDA (Lower Cambrian to Mid Cambrian)
        The cephalon is semicircular with a typically long glabella. Eyes are large
        and semicircular. the thorax has numerous segment >60. the pygidium is
        typically very small.
       Suborders: Olenellina and Redlichiina.
     ORDER AGNOSTIDA (Lower Cambrian to Upper Ordovician)
         typically very small (only a few mm). The cephalon and pygidium are similar in
         shape and size. There is normally only two thoracic segments.
         Suborders: Agnostina and Eodiscina.
ORDER CORYNEXOCHIDA (Lower Cambrian to Mid Devonian)
  Glabella is elongate and often concave. Eyes are typically large. 7-8 thoracic
  segments normal. Pygidium large and sometimes spinose.
  Suborders: Corynexochina, Illaenina and Leiostegiina.
ORDER LICHIDA (Ordovician to Devonian)
  Typically spiny. Thoracic segments vary between 8-13. Pygidium often longer than
   width and ending in spiny tips
  Suborders: Lichoidea, Odontopleuroidea and Dameselloidea.
ORDER PTYCHOPARIIDA (Lower Cambrian to Upper Ordovician)
Very large order. problems with classification. Thorax typically large with over 8 segments. The pygidium can by quite variable but typically small.
Suborders: Ptychopariina and Olenina.
ORDER HARPETIDA (Upper Cambrian to Late Devonian)
Small order. Cephalon semi-circular to ovate with a flat, convex or concave brim. Thorax with over 12 segments and a small triangular pygidium.
 Families: Entomaspididae, Harpetidae, Harpidadae.
ORDER PHACOPIDA (Lower Ordovician to Upper Devonian)
  Large eyes. 8-19 thoracic segments. Pygidium can vary in size and shape gratly.
  Suborders: Calymenina, Phacopina and Cheirurina.
ORDER ASAPHIDA (Mid-Upper Cambrian to Upper Ordovician-
    Lower Silurian)
  Cephalon often equal to pygidium. Eyes usually large. Thoracic segments range
  from 5-12 segments. Pygidium typically large.
  Superfamilies: Anomocaroidea, Asaphoidea, Dikelokephaloidea,
  Remopleuridoidea, Cyclopygoiddea and Trinucleioedea.
  ORDER PROETIDA (Ordovician to Permian)
   Typically small. Large glabella. Thoracic segments vary from 8-22. Pygidium often 
   Superfamilies: Proetoidea, Aulacopleuroidea and Bathyuroidea.

Websites produced by students on the MSc Palaeobiology programme in the Department of Earth Sciences at the University of Bristol for academic year 2003-4