Trilobites Flashcards
Phylum and class?
Arthropoda
Trilobita
Exoskeleton?
Chitin
Three main body parts
Cephalon, thorax, pygidium
How does it breathe?
Gills attached, underneath pleuron with appendages
Describe morphology of cephalon
Several structures, compound eyes, facial sutures, free cheek, fixed cheek and glabella. Spines may be attached at genal angle, for defence or to spread mass
Describe morphology of the thorax
Made up of thoracic segments, each has pair of appendages and gills, two pleurae and segment from axis. Many articulated plates which may enable it to enroll
Describe morphology of the pygidium
Several segment fused together
What is ecdysis?
Exoskeleton cannot grow so is shed. Fractured along lines of weakness like facial sutures, separated fixed cheek from free cheek, animal wriggles out, period of rapid growth before new skeleton forms
When did trilobites live?
Cambrian to Permian-died at end Permian extinction, peaked in Ordivician
Example of epifaunal trilobite
Calymene
What morphological features did Calymene posses?
Many pleura, to support many legs and gills, flexible so could enroll
Compound eye, ability to see 360 degrees, so safe from predation, may be active hunter
Large and not streamlined, didn’t need to swim or float, walked on sea floor
Name a pelagic trilobite
Agnostus
What morphological features did Agnostus possess?
No eyes, did not need to hunt for food as filter feeder
Very small and light, so could easily float in water column
Inflated glabella, filled with gas for buoyancy
Few pliers, didn’t swim, limited flexibility
Name a nektonic trilobite
Dephion
What are the morphological features of Dephion?
Eyes on stalks, could see all around it
Inflated glabella for flotation
Very small size, light to stay afloat
Numerous separated pleura with spines, could be used to paddle, increase surface area for buoyancy
