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
spineless.
Superfamilies: Proetoidea,
Aulacopleuroidea and Bathyuroidea.
