Compare the above pictorial approach to the narrative description
(pictorial features highlighted above are boldfaced green below):
Introduction: large and variable group of related suborders.
Cephalon: typically proparian (Phacopina and Cheirurina) or gonatoparian (Calymenina), preglabellar field often very short or absent, 4 or fewer pairs of glabellar furrows (these sometimes fused); eyes, when present, schizochroal (Phacopina) or holochroal (Cheirurina and Calymenina); with rostral plates (Calymenina and Cheirurina) or without (some Phacopina); hypostome conterminant (all suborders) to impendent (some Phacopina).
Thorax: 8 – 19 segments, sometimes distinctly furrowed, axis sometimes broad (e.g., Homalonotidae).
Pygidium: typically micropygous (most Calymenina and Phacopina), but variable (e.g., subisopygous in Dalmanitoidea and Acastoidea), may be lobed or spiny (e.g., Cheirurina, some Dalmanitoidea, Acastoidea), or smooth-margined, with round or subtriangular outline (e.g., Calymenina, Phacopoidea).
Other: All suborders share similar ontogeny (particularly in the protaspides) that in particular link the Calymenina to other Phacopida.
Occurrence: Lower Ordovician (Tremadoc) to Upper Devonian (Famennian)
Suborders: Calymenina, Phacopina, Cheirurina.
PHACOPIDA includes three Suborders
Return to Phacopida Fact Sheet
Walking Trilobite animation ©2000 by S. M. Gon III
All line drawings this page ©1999 - 2005 by S. M. Gon III