Evolved in cambrian + became extinct at end of the Permian
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exoskeleton
made of chitin; provides protection and support; provides attachment for muscles; may have had sensory hairs emerging from the exoskeleton to detect chemicals/changes in the environment
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exoskeleton morphology
made up of 3 layers. A waxy outer layer and 2 further layers of chitin and protein. The middle layer may be impregnated with calcium carbonate for increased strength
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appendages
term for jointed legs and antennae. used for moving and feeding
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pleuron
segment adjoining the axis. each had a pair of jointed legs, probably used for walking or swimming
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gills
for respiration. feathery structure used for gas exchange. positioned above the legs, so it didn't drag on the sea floor
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Cephalon morphology; Appendages-headlegs
feeding and sensory role to detect environment and feeding
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Cephalon morphology; Antenna
to detect environment. part of sensory system
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cephalon morphology; Glabella
formed by the presence of the stomach, which is inside the head. shape may indicate diet
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cephalon morphology; compound eye
made up of many calcite plates, for wide-angled vision. part of sensory system
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cephalon morphology; free cheek
part of cephalon that breaks away from the skeleton during ecdysis
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cephalon morphology; facial suture
a line of weakness where the exoskeleton breaks first during ecdysis
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cephalon morphology; fixed cheek
part of cephalon that remains attached to the exoskeleton at the beginning of ecdysis
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cephalon morphology; genal angle
part of cephalon which may have spines attached. actual angle can be measured in some species
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thoracic segment
made up of 3 articulating plates; very flexible; ability to enroll(defensive mechanism)
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Thorax morphology
made up of thoracic segments, each possessing a pair of appendages, gills in life and a segment from the axis
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thorax morphology; pleuron
segment adjoining axis; may also have spines extending from them
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appendages: walking/swimming legs
for locomotion and gill attachment
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Pygidium
fused tail piece(several segments fused together); may have spines. this may stabilise the animal
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Benthonic
organism lives on or in the sediment substrate of the sea floor/ river bed
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infaunal
organism lives in the sediment, usually in a burrow. many will filter feed
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