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Arthropods
 ARTHROPODS
 1 million known species of
arthropods.
 May be up to 30 million species
in the world’s tropical rain
forests. Two out of three
animals living on earth are
arthropods.
Phylum Arthropoda
 Arthron- means joint
 pous- means foot
 Typical arthropod: an invertebrate
with bilateral symmetry, a coelom,
an exoskeleton, jointed appendages,
an open circulatory system and
complex social behavior.
 Arthropods include:
insects,
centipeds, millipeds, spiders, ticks,
scorpions, mites, lobsters, shrimp,
crabs, and crayfish.
 Evolutionary success due to
jointed appendages and
exoskeleton.
 Jointed appendages: most
recognizable feature. Allow
for more powerful
movements and allows
appendages to be used for:
 1)walking,
 2)sensing
 3) feeding
 4) mating.
***Appendage may be a leg
or an antenna.
Exoskeleton –
Hard, thick
outer covering made of protein and
chitin. It may be one continuous
covering or it is made of separate
plates held together by hinges.
 Provides: protection and support for
internal tissues
 protects against water loss
 provides places for muscle
attachment
 Disadvantage:
Exoskeletons are heavy some have adapted to
their habitats by
developing thinner,
lightweight exoskeleton.
However, this provides
less protection.
 Molting –
periodic shedding of
exoskeleton
 allows the animal to grow larger;
 4 to 7 times in their life
 during molting animal is
vulnerable to predators
Process of
Molting:
 animal contracts muscles in the rear
part of its body, forcing blood
forward.
 The forward part of the body
swells, causing the old exoskeleton
to split open.
 The animal then wiggles out.
Segmentation
 Less segmented than worms; the
body segments have become
fused into 1-3 body sections
 1) HEAD
 2) THORAX
 3) ABDOMEN
Some arthropods have
the head and thorax
fused to form a
cephalothorax
 Efficient gas exchange
 Arthropods are generally quick,
active animals. They crawl, run,
climb, dig, swim, and fly. Some
flies beat their wings 1000 times
per second. Oxygen delivery to
cells must be quick.
 3 Types of Respiratory Structures
 1. gills – aquatic (Ex. Crabs)
 large surface area enables a large
amount of blood-rich tissue to be
exposed to water containing oxygen.
2.tracheal tubes – land (most insects)
 most insects
 branching network of hollow air passages
that carry air throughout body; air
enters and leaves through openings on
the thorax and abdomen called spiracles.
 3. book lungs – land
 Spiders
 are air filled, folded
membranes that
contain leaf-like plates
(looks like pages in a book)
which increase the surface
area of tissues exposed to
air.
Book Lungs
 Arthropods have acute senses
 Movement, sound, or chemicals can
be detected by antennae. Antenna
are also used for communication,
detect pheromones. Example ants
use it for scent trails and for mating.
 Acute vision – most have
one pair of large compound
eyes and 3 to 8 simple eyes.
 Simple eye – visual structure with
only 1 lens, used for detecting
light.
Side eyes: pick up movement
Middle front: sharp images, some color
Side front: judge distances
 Compound eye – many lenses
that register light from one area of
the total field of view; can detect
slight motion of prey, mates, or
predators; can see colors, but
image is fuzzy.
 SYSTEMS
 Nervous system – well
developed; consists of
 1) ventral nerve cord
 2) anterior brain
 3) several ganglia (nerve &
tissue cells)
circulatory (yellow),
digestive (green),
nervous (blue) systems.
 Open Circulatory system – one or more
hearts; blood flows out of vessels, bathes
the tissue, returns to heart through open
body spaces.
 Complex Digestive System
 1) mouth – contain a variety of jaws called
mandibles; mouthparts are adapted for
holding, chewing, sucking or biting, this
enables them to fit a variety of niches.
•Sand flies feed by drawing
blood
•Butterflies and moths use a
rolled-up sucking tube
Sponging tongue of
housefly uses saliva to
digest food
 Most terrestrial arthropods
excrete wastes through
Malpighian tubules. They are
located in the abdomen, attached
to and empty into the intestine
 Muscular System – attached to
exoskeleton
How far can a flea jump?
 Reproductive System – most species
have male and females that
reproduce sexually
 Terrestrial arthropods – internal
fertilization
 Aquatic arthropods - external
fertilization
 Some species are
hermaphrodites (animals w/both
male and female organs).
 Some species are asexual.
Reproducing through a process
called parthenogenesis (organism
develops from an unfertilized
egg).
ECOLOGY OF ARTHROPODS
 Found in a wide variety of habitats due to
the variety of adaptations they have for
obtaining and digesting food. Some are
consumers and others are parasites
(some lay eggs on the larvae of other
insects).
Beneficial to humans
1) pollinate flowering trees and
crop plants
2) wax
3) silk
4) provide alternatives (ladybird
beetles) to chemical
 5) control of other insects
 Research on arthropods has led to
advances in the fields of genetics,
evolution, and biochemistry. From crab
shells, scientists have made artificial skin,
surgical sutures, and anti-fungal
medication.
But, they can also be detrimental to humans.
 1) Spread diseases to plants and animals
(West Nile, malaria, yellow fever, Lyme’s
disease)
 2) Eat crops.