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Arthropods
Arthropods (Arthropoda – whose name means joint footed) make up about three-quarters of all known invertebrates.
All arthropods are symmetrical about a line down the centres of their bodies. The body is also divided into segments, and the segments each bear pairs
of jointed limbs, wings or jaws. The soft parts are protected by the ‘shell’ (exoskeleton), which is on
the upper (dorsal) side of the animal. Because the arthropods are invertebrates, their bones cannot grow steadily, but must be shed and re-grown periodically. The shedding of shells results in large amounts of fossil material.
The arthropods are divided into insects, spiders, crustaceans (crabs, etc.), centipedes and millipedes, and trilobites.
Many insects and spiders have delicate bodies that are not well preserved as fossils except in special circumstances, such as when they are found in amber. Fossils from crustaceans are more common. Trilobite remains are also commonly preserved.
(Above) Tertiary insect in amber.
(Above) A cirripede (barnacle).
(Above) A Carboniferous beetle.
(Above) A eurypterid.
(Above) Limulus, the king crab.
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