Subphylum Trilobitomorpha

• Parts of Trilobite

  A) Cephalon

  B) Thorax

  C) Pygidium

  
• Fossil trilobites, belong to the Paleozoic era
• "Trilobite" means three-lobed and it refers to the transverse trilobation (axial lobe + left and right pleural lobe) of the dorsal body surface
• body

  oval, flattened with dorsal cuticle; forms are dictated by the mode of existence that may be burrowing, benthic crawling, and planktonic swimming
• 3 larval stages of development

  • Protaspia: planktonic with carapace
  • Meraspia: carapace, pygidium & some developing trunk appendages present
  • Holaspia: adult features are evident
• Cephalon

  bears a ventral mouth, a pair of ventral antennae, with biramous appendages, distal tips of which bifurcates
• Thorax/trunk

  • segments are separated, each bearing a pair of biramous appendages
  • with telopodite (inner walking leg) & pre-epipodite (outer gill bearing branch)
• Pygidium

  • fused segments with reduced appendages
  • possesses lateral lobes & middle axial lobe arising from 3 longitudinal divisions made by a pair of furrows from anterior to posterior
• Protaspia

  the larva (protaspis) is composed od of an unarticulated exoskeletal shield, and often very simple in form
• Meraspia

  marked by a body with 2 or more articulated segments, and during this period, each molt meant the potential addition of usually one or two, but rarely greater numbers of articulated thoracic segments to the body of the growing trilobite
• Holaspia

  when the number of thoracic segments reached that of adult specimens, this marked the holaspid period; the last period of development
• Phylum: Arthropoda

  Subphylum: Trilobitomorpha

  Class: Trilobita

  Order: Ptychopariida

  Family: Olenidae

  Genus: Balnibarbi