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Arthropods
Arthropods
• Arthropods are the most diverse and
numerous animals on earth
• More than 1 million different species have
been identified
• They thrive in almost every habitat
• There worldwide population is estimated at a
billion billion, or 1018 individuals
General Characteristics of the Phylum
Arthropoda (Arthropods)
• Arthropods are characterized by there segmented
bodies, jointed appendages and hard exoskeletons
• The exoskeleton is composed of chitin
• In most arthropods the segments are called the
head, thorax and abdomen
• The head contains the antennae and mouth pieces,
the thorax supports the legs and wings and the
reproductive organs are found in the abdomen
General Characteristics of the Phylum
Arthropoda (Arthropods)
• As arthropods grow, they will outgrown the
chitinous exoskeleton. They will shed the
exoskeleton in a process called molting
General Characteristics of the Phylum
Arthropoda (Arthropods)
• All arthropods have an open circulatory
system in which blood is pumped from a tubelike heart to bath the internal organs
• All arthropods have a ventral nerve cord and
brain
• Along the nerve cord are specialized nerve
cells called ganglia
• Most arthropods have compound eyes
General Characteristics of the Phylum
Arthropoda (Arthropods)
• Aquatic arthropods have gills used for
respiration
• Terrestrial arthropods have tracheae, which
are chitin lined tubes that lead from the
internal organs to the outside of the body
where they end in little holes called spiracles
that are used for breathing
Overview of Arthropod Diversity
• Arthropods first evolved in the sea about 560
million years ago
• A good example of an early extinct arthropod
is called a trilobite
Overview of Arthropod Diversity
• One ancient living arthropod is the horseshoe
crab, which have been living virtually
unchanged for over 300 million years
Overview of Arthropod Diversity
• Modern arthropods include the crustaceans,
arachnids, insects and myriapods
Crustaceans
• The crustaceans include the lobsters, crabs,
shrimp and barnacles
• Crustaceans have specialized appendages
(claws or chelipeds) often used for fighting
Terrestrial Arthropods
• The three groups of terrestrial arthropods
include the arachnids, insects and myriapods
• The arachnids include the spiders, ticks,
scorpions and mites
• The insects include beetles, ants,
grasshoppers, butterflies and dragonflies
• The myriapods include centipedes and
millipedes
Metamorphosis
• Insects undergo metamorphosis a process by
which the body changes from a sexually
immature phase to the mature adult phase
• Once metamorphosis is complete the adult no
longer grows
• Both molting and metamorphosis are
controlled by hormones
Metamorphosis
• Incomplete metamorphosis (grasshoppers)
the immature young look like the adults but
lack wings and sexual organs
• Complete metamorphosis (butterflies) the
larval stage looks and functions much
differently from the adult stage