Arthropods
Phylum Arthropoda Arthropods
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Largest and most successful phylum
75% of all animals!
Segmented body
Tough exoskeleton
Joint appendages (legs and
antennae)
Cephalization
Bilateral Symmetry
 Exoskeleton:
an external covering
that protects and supports the body
– Made from chitin
– Varies in size, shape, and roughness.
Firm
and leathery (caterpillars)
Tough and hard (crabs and lobsters)
Waxy (land dwelling arthropods)
Evolution of Arthropods
 Evolution
of
Arthropods
 Typical
primitive
arthropod:
– many identical
segments with a
pair of appendages.
 Evolution
led to
fewer segments and
specialized
appendages
Fossilized Trilobites
Feeding
 Feeding
– Includes herbivores, carnivores,
omnivores, detritivores, filter feeders,
bloodsuckers, and parasites.
– Mouth parts adapted to type of food
eaten
 Pincers,
fangs, jaws
RESPIRATION
• Terrestrial arthropods:
breathe through
tracheal tubes
Spiracles
• Air enters and leaves
tracheal tubes through
spiracles
•
small openings located
along the side of the body.
Tracheal tubes
Tracheal tubes
RESPIRATION CONTINUED…
•Book lungs organs that
have layers of respiratory
tissue (stacked like pages of
a book.)
•Spiders, scorpions,
horseshoe crabs
Circulation and Excretion
 Arthropods
system
have a open circulatory
No distinction between blood and other
fluids
 Malpighian
tubules (terrestrial): saclike
organs that extract waste from the
blood
 Diffusion (aquatic)
Response and Reproduction
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Response
– Well developed nervous system
– Brain serves as central switchboard
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Reproduction
– Terrestrial arthropods: internal fertilization
 Place
sperm inside female OR deposit sperm packet
– Aquatic arthropods: internal or external
Reproduction
 Separate
sexessexual reproduction
 Males directly transfer sperm to
females
 Ex. Barnacle stretches out
appendage to local females
 Mating occurs after female molts
MOVEMENT
 Movement:
Groups of well
developed muscles coordinate
movement
– generating force by pulling on the exoskeleton
– Muscles flex (bend) or extend (straighten) the
joint.
Growth and Development
Arthropods will outgrow their exoskeleton
and undergo a period called molting.
 Molting: the shedding of its entire
exoskeleton
– New/soft skeleton starting to form
– Controlled by the endocrine system
– Molting Cicada Video
– http://upload.wikimedia.org/wikipedia/c
ommons/6/62/Cicada_molting_animate
d-2.gif
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Groups of Arthropods
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Classified by number of body
segments and mouth parts
3 major groups
1. Crustaceans
2. Spiders and their relatives
3. Insects and their relatives
1) Crustaceans
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Primarily aquatic
– Includes crabs, shrimps, lobsters, crayfishes,
and barnacles.
– 2 pairs of antennae, two or three body
sections, and chewing mouthparts called
mandibles.
Abdomen
Cephalothorax
Antennae
Antennules
Mandible
Body Plan of Crustaceans
swimmerets
Cheliped
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Cephalothorax
– Fusion of head with
the thorax
Mandible:
– Mouthpart adapted
for biting and
grinding food
•Cheliped: first pair of
legs that have large
claws modified to catch,
pick up, crush, and cut
food.
•Swimmerets: flipperlike appendages used for
swimming
1) Small Crustaceans
 Copepods-
extremely abundant,
planktonic, filter feed
 Barnacles- usually sessile, filter
feed, body enclosed by calcareous
plates
 Krill- planktonic, shrimp-like, have
carapace to cover anterior, filter
feed
True Crabs
 Small
abdomen and tucked under
cephalothorax
 V-shape ab. in males
 U-shape ab. in females
 Largest and most diverse of
decapods
 Scavengers and predators
Male Jonah Crab
Female Jonah Crab
2) Chelicerates
 Horseshoe
scorpions
crabs, spiders, ticks, and
– No antennae
– Have mouthparts called chelicerae
– 2 body sections
– 4 pairs of walking legs
 Divided
into 2 main classes:
 Merostomata
(horseshoe crabs)
 Arachnida (spiders, mites, ticks, and
scorpions)
Horseshoe crabs
Horseshoe Crabs
 Appeared more than 500 million years ago
– changed little since that time.
 Have
chelicerae, five pairs of walking legs,
and a long spike-like tail (telson) that is used
for movement.
Horseshoe Crab
1. Carapace
 2. Telson
 3. Compound eye
 4. Anterior spine
 Five pair of legs
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Spiders
 Food
and Digestion
– Spin webs of a strong, flexible protein
called silk
– No jaws for chewing
 must
liquefy food using enzymes
 Use fanglike chelicerae to inject paralyzing
venom
What does the spider use silk for?
Silk glands
Spinnerets
Mites, Ticks, and Scorpions
Mites and ticks are small arachnids that
are often parasitic
 Ticks can transmit bacteria that cause
serious diseases
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– chelicerae and pedipalps are specialized for
digging into a host’s tissues and sucking out
blood
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Scorpions inhabit warm areas around the
world.
– Chew their prey
3) Uniramians
 Centipedes,
millipedes, and insects
 Characteristics of Uniramians
– Have jaws
– One pair of antennae
– Un-branched appendages
– Carnivores
Class Insecta (Insects)
 Characteristics
of Class Insecta
– Contains most species of any other
animals
– Body divided into 3 segments
 Head,
thorax, and abdomen
Characteristics continued…
 Segmented
body
 Exoskeleton
 Jointed
appendages
 A typical insect also has:
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a pair of antennae
a pair of compound eyes
two pairs of wings on the thorax
tracheal tubes that are used for respiration
Response
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Compound Eye: made up of many lenses
– Detect minute changes in color and movement
– Information from eye is assembled in the brain
and directs the insects response
Chemical receptors for taste and smell
– Located on the mouthparts, antennae, and
legs
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Sensory hairs: detect movement in
surrounding air or water
 Well developed ears
Feeding and Specialized Mouth
Parts
3
pairs of appendages that are used
as mouthparts, including a pair of
mandibles
Ant
Specialized mouth parts
continued…
Spongelike mouthpart used to lap up food
Fly
Specialized Mouth Parts
Tubelike mouthpart used to suck nectar
Moth
Movement and Flight
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pairs of legs used for walking,
jumping, capturing and holding prey.
– Legs have spines and hooks that are
used for grasping and defense.
 Flying
insects typically have two
pairs of wings made of chitin
Metamorphosis
 Process
of changing shape and form
– Insects undergo either incomplete
metamorphosis or complete
metamorphosis
 Incomplete
Metamorphosis
– Look very much like adult form
– Immature forms are called nymphs
 lack
functional sexual organs and wings
Complete Metamorphosis
 Animals
hatch into larvae that look
and act nothing like their parents
 Feed and grow rapidly and molt a
few times
 Undergo a final molt and change into
a pupa
– stage in which an insect changes from
larva to adult.