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ARTHROPODS: SPIDERS

ATHROPODS

      While the body of arthropods is segmented, this segmentation is less obvious in the bodies of some adult arthropods (such as beetles and crabs) because of the fusion of embryonic segments.  Complex structures (such as the head of insects) are thought to have resulted from the fusion of a number of ancestral segments.  The arthropod exoskeleton is made of chitin and offers protection from predators and water loss in addition to allowing movement.

CHELICERATES

TARANTULA TARANTULA

     Scorpions, spiders, ticks, mites, and horseshoe crabs are classified as chelicerates.  They typically possess six pairs of appendages, the first pair of which form mouthparts called chelicerae which are often modified to form pinchers or fangs.  The second pair of appendages may form pedipalps which manipulate food, leaving on four pairs of appendages to be classified as legs (as in spiders).  There are no antennae and the body typically possesses two segments.

     All spiders are carnivores which feed primarily on insects, although large spiders can even kill small vertebrates. 

SPIDER
SPIDER SPIDER

Some spiders (wolf spiders, jumping spiders, and crab spiders) hunt for prey or ambush them.  Most spiders possess thin structures at the tips of their abdomens called spinnerets which produce silk.  Webs produced by silk may be irregular in shape with fibers going in all directions or they may have definite patterns in flat planes or funnels.  Some spiders spin silk from an elevated position so that the wind may carry them for some distance.

     Female spiders are often much larger than males.  Spider eggs are wrapped in silk cases.

WEB
WEB SPIDER
SPIDER SPIDER
SPIDER SPIDER