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Domain: Eukaryote
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerates
Includes Classes:
◦ Arachnida
 Spiders scorpions mites ticks
◦ Pycnogonida –
 Sea spiders
◦ Merostomata –
 Horseshoe crabs
 Eurypterids (NYS Fossil)
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Four pairs of legs (1)
◦ (horseshoe crabs have five pairs)
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Two body segments
◦ Cephalothorax (2) - contains brain, eyes,
mouth, walking legs
◦ Abdomen (3) – contains most internal
organs
NO antenna
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Chelicerae –
◦ Mouthparts
◦ Contain fangs to stab prey and venom to paralyze
prey
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Pedipalps – longer than chelicerae
◦ appendages near mouth modified to grab prey
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Respire (breathe) with book lungs or book
gills
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Air flows over folded surfaces that
look like pages from a book
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Among oldest living arthropods
(~ 500mya)
Heavily armored like crabs
Their anatomy is closer to that
of spiders.
Five pairs of legs
Long spike like tail used for
movement
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Spiders do not have jaws for chewing
They first inject prey with paralyzing venom
Then liquefy their food before swallowing by
injecting enzymes into their prey and
Suck the juice into their stomach
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Spinnerets at the end of the
abdomen contain organs that
produce silk.
Silk can be used for webs,
create egg cocoons, wrapping
prey and other structures
(trap door)
Programmed behavior –
◦ can start almost as soon as they
are hatched
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Often parasitic
Chelicerae and pedipalps specialized to dig
into host tissues and suck out blood and
fluids
◦ Chelicerae used to pierce the skin
◦ Pedipalps used to hold onto skin
Can be vectors (transmit diseases)
◦ Ticks carry bacteria that cause diseases
 Lyme disease
 Rocky Mountain spotted fever
◦ Mites cause itching or rashes
 Mange, scabies
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Widespread in warm areas of
world
Can chew prey using their
chelicerae
Pedipalps are enlarged to form
claws
Long segmented abdomen
carries a venomous stinger
that can kill or paralyze prey.