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Chapter 28
28.1 Arthropod?
Chapter 2
A. What is an Arthropod?
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1. Pollinate many of the flowering plants on Earth
a. Some even spread disease
2. A typical arthropod is segmented, coelomate
invertebrate, with bilateral symmetry
3. They have an exoskeleton, and jointed structures
called appendages
a. An appendage is any structure, that grows out
of the body of an animal
b. Highly adapted for a variety of purposes
including sensing, walking, feeding and mating
4. Earliest known invertebrates to have jointed
appendages
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A. Arthropod ( cont )
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5. Jointed appendages are great because they allow
more flexibility in the exoskeletons
a. Better movement, and stronger animal
6. Exoskeleton
a. Hard, thick, outer covering made of protein and
chitin
b. Some exoskeleton cover most of the body,
others protects and support the internal tissues
and a place for muscle attachment
c. Some are covered by a waxy layer to protect
from water lost
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A. Arthropods ( cont )
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7. Some Molt the exoskeleton
a. Because they are heavy structures, on most
they must periodically shed the old
b. A new soft exoskeleton form
c. When molting occurs, the animal rear par t of
body forces blood forward and the forward part of
the body swells, splitting the old and the new
exoskeleton hardens into a larger size allowing the
animal to grow larger into the new shell
D. About 4 to 7 times during their life
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B. Segmentation in Arthropods
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1. Segments have been fused into three body parts
a. Parts are head, thorax and abdomen
2. In some arthropods the two body parts also fuse
together Cephalothorax ( head and thorax fused
together)
3. Based on this; Beetles have separate head and
thorax and can move easier
4. Lobsters have a Cephalothorax and are limited in
movement
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C. Systems
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1. Respiratory
a. Quick creatures that run, fly, swim, dig, climb
b. Some flies beat their wings as fast as 1000 times per
second
c. Efficient respiratory structures
d. There are three types of respiratory structures
 1 Gills, tracheal tubes, and book lungs
e. Most insects have tracheal tubes which is a branching
networks of hollow air passages that carry air throughout the
body
 1 Muscle activity helps pump the air through body
 2 Air enters and leaves tubes through openings on the
thorax and abdomen called spiracles
f. Spiders have book lungs, air filled chambers that contain
leaf-like plates
 1 The stacked plates are like pages of a book
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C. Senses ( cont )
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2. Acute senses
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a. Quick movements because of strong
muscular contractions
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b. So can respond to a variety of stimuli
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c. Movement, sound, and chemicals can be
detected
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d. Antennae are also used for communication
as well as pheromones
1 Pheromones are chemical odors given
off that the antennae can sense
e. Accurate vision is also important
1 Most have 1 pair of compound eyes,
but some have simple eye
2 Simple eyes have only one lens
3 Compound eyes have many lenses
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C. Systems (cont)
 3. Nervous systems
a. Well developed
b. Consists of a double ventral nerve cord, and
an anterior brain, and several ganglia
c. Ganglia act as control centers for body
section in which they are located
 4. Other systems
a. Circulatory
 1 one or more hearts in an open circulatory
system
 Blood flows out of the vessels, bathes the
tissues of the body, and returns to heart
through open body spaces
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C. Systems ( cont )
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4. Other systems ( cont )
b. Digestive
 1. Mouth, stomach, intestine, and anus
 2. Have various glands that produce digestive
enzymes
 3. Mouth consists of mandibles ( jaws )
adapted for holding, chewing, sucking, or biting
c. Excretion
 1. Have malpighian tubes located in the
abdomen
a. Attached to intestine and empty it
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C. Systems ( cont )
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4. Other systems ( cont )
d. Muscular
 1 muscles are attached to the inner surfaces of
exoskeleton on both sides of the joint
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C. Systems ( cont )
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5. Reproduction
a. Separated sexes and internal reproduction in
land and external in aquatic
 1 Some like barnacles are hermaphrodites
 2 Some including bees, exhibit
parthenogenesis
a Form of asexual reproduction in which a
new individual develops from an unfertilized
egg
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D. Diversity
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1. There are more arthropods species than
all other animal species combined
a. See problem-solving lab on page 766.
Diversity
Arachnids
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Class Arachnida
Only two body regions
First pair of appendages called chelicerae
Located near mouth
Modified pincers or fangs
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2nd pair called pedipalps
For handling food and sensing surroundings
Diversity
Spinnerets- structure used to make webs
Other archnids
Ticks, mites, scorpions
Ticks and mites only have one body region
Crustaceans
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Only arthropod to have two pair of antennae
All have mandible for crushing food
Move side to side
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Two compound eyes usually on stalks
Diversity
Many have 5 pair of walking legs
Live in moist environment to aid in
respiration
Class Chilopoda- centipedes
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Carnivorous
Have malpighian tubules for waste removal
Class Diplopoda- millipedes
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Eat mostly plants
Diversity
Centipedes and millipedes have tracheal
tubes instead of book lungs for gas
exchange.
Class insecta- the insects
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Mate only once (or some, a few times) during
life
Have internal fertilization
Large number of eggs assures some will
survive
Diversity (insects)
Metamorphosis- in some cases, adult
insect does not look at all like the juvenile
stage
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Series of chemically controlled changes
Usually 4 stages: egg, larva, pupa and adult
Pupa is a period of reorganization
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Ex. Caterpillar turning into a butterfly
Complete metamorphosis is an advantage
because adult does not compete with larva for food
Diversity (insects)
Incomplete metamorphosis
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Three stages: egg, nymph, adult
Nymphs have same general appearance as
adult but may lack some general features
Success
Success of arthropods can be attributed to
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Varied life cycles
High reproductive output
Structural adaptation
Small size
Hard exoskeleton
Jointed appendages
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Most likely evolved from Annelids