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Phylum Arthropoda
(jointed foot)
Page 715
Arthropods are classified based on the number
of body segments they have and the
appendages attached to these segments.
• Arachnids (spiders, scorpions and ticks)
• Crustaceans (lobster, crabs, barnacles, krill,
• Centipedes and millipedes 
• Insects (bugs, grasshoppers, flies, bees, ants)
• First appeared in the sea over 600 million
years ago.
• First arthropods had many body segments.
Some have evolved to have just two or three.
• Major characteristics of Arthropods?
– Jointed appendages (structures that extend from
the body---legs, antennae)
– Segmented bodies
– Exoskeleton made of protein and chitin
• Why must an arthropod molt its exoskeleton?
• You are a molting arthropod…
What would you be doing? Where would you be?
Form and function in arthropods
Feeding: omnivores, herbivores and carnivores
with a variety of suitable adaptations.
Respiration: Most terrestrial arthropods breath
through a network of branching tracheal
tubes that are throughout the body. Air enters
and leaves the tracheal tubes through small
openings called spiracles. Spiders have book
lungs- layers of respiratory tissue stacked like
a book. Most aquatic arthropods have gills.
How gills work
Circulation – Open circulatory system. Welldeveloped heart that pumps blood through
vessels. Blood leaves vessels and moves
through cavities. Finally collects in a large
sinus surrounding the heart, re-enters the
heart and is pumped around again.
Excretion: Most terrestrial arthropods dispose of
nitrogenous wastes using Malpighian tubulessaclike organs that extract waste from the
blood and add them to feces. Cellular waste
of aquatic arthropods is released directly into
the water.
Response: Well-developed nervous system with
a brain and sophisticated sense organs (ie.
compound eyes)
Movement: Well-developed muscle systems
controlled by the nervous system. (see
diagram page 718)
Terrestrial: internal fertilization
Aquatic: external fertilization – females
release eggs and then males release sperm
over them.
• 2 segments
• 4 pairs of appendages
• Spin webs made of silk
using their spinnerets
which are located near
the back of their
• Also use silk to wrap
prey and baby spiders
sometimes use it as a
balloon to float away.
• Some spiders chase their prey.
• First set of appendages have poison (fangs!)