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Chapter 28 Power Point


									     Chapter 28:
        Section 1:
Introduction to Arthropods
     Introduction to Arthropods
• Arthropod – animal having a segmented
  body, an exoskeleton containing chitin, and a
  series of jointed appendages; belong to the
  phylum Arthropoda
   – More than 1 million species have been
   – Vary enormously in size, shape, and habits
   Diversity and Evolution in Arthropods
• Arthropods are divided into four subphyla:
   – Trilobita
       • Oldest subphylum of arthropods
       • Trilobites were dwellers in ancient seas
           – Extinct
   – Chelicerata
       • Chelicerates include spiders, ticks, mites, scorpions, and
         horseshoe crabs
   – Crustacea
       • Crustaceans include such familiar (and edible) organisms
         as crab and shrimp
   – Uniramia
       • Uniramians include most arthropods: centipedes,
         millipedes, and all insects—including bees, moths,
         grasshoppers, flies, and beetles
                      Spotted Cleaner Shrimp
Flat Rock Scorpions
Form and Function in Arthropods
• All arthropods exhibit several key features
  – 3 most important features
      • Tough exoskeleton
      • Series of jointed appendages
      • Segmented body
  – Other characteristics
      • Brain located in dorsal part of head
      • Ventral nerve cord
      • Open circulatory system powered by a single
                           Deer Tick
California Spiny Lobster
          The Arthropod Body Plan
• The exoskeleton is a system of external supporting
  structures that are made primarily of the
  carbohydrate chitin
• Provide excellent protection from physical damage
• Waterproof (terrestrial)
   – Prevents water loss
• Helps arthropods move efficiently and adapt to their
• Disadvantages
   – Cannot grow as the animal grows
   – Movement can occur only at the joints of the
         The Arthropod Body Plan
• All arthropods have jointed appendages that
  enable them to move
• Over millions of years, appendages have
  evolved into marvelously versatile adaptations
  to different environments
   – Antennae
   – Claws
   – Walking legs
   – Wings
   – Flippers
• All arthropods have segmented bodies
• Appendages enable these animals to eat almost
  any food you can imagine
• Exhibit every mode of feeding
   – Herbivores
      • Some eat any plant, others are more
   – Carnivores
      • Some catch and eat other animals, others
        feed on animals that are primarily already
– Parasites
   • External parasites drink blood or body
     fluids from animals, internal parasites
     passively absorb nutrients through
     body walls
– Filter feeders
   • Use comb like bristles on mouthparts
     or legs to filter plants and animals from
– Detritus feeders
                   Lubber Grasshopper--

Praying Mantis--
• Have evolved three basic types of respiratory
  structures—gills, book gills and book lungs,
  and tracheal tubes
   – Most have only one of these respiratory
      • Aquatic arthropods have gills just under
        the cover of their exoskeleton
          –Are formed from part of the same
           appendages that form mouthparts and
• Book gills (horseshoe crabs) and book lungs
  (spiders and their relatives) are unique to these
    – Several sheets of tissue are layered like the
      pages of a book
    – Increase the surface area for gas exchange
• Tracheal tubes (terrestrial arthropods)
    – From spiracles, long branching tracheal tubes
      reach deep into the animals’ tissues
    – Supplies oxygen by diffusion to all body
    – Work well in only small animals
Fiddler Crab--Gills
           Internal Transport
• A well-developed heart pumps blood through
  an open circulatory system
• When the heart contracts, it pumps blood
  through arteries that branch into smaller
  vessels and enter the tissues
• There the blood leaves the vessels and moves
  through spaces in the tissues called sinuses
• Eventually, the blood collects in a large cavity
  surrounding the heart, from which it re-enters
  the heart through small openings and is
  pumped around again
• Undigested food becomes solid waste that
  leaves through the anus
• Most terrestrial arthropods dispose of nitrogen-
  containing wastes by using a set of Malpighian
   – Bathed in blood inside the body sinuses
   – Remove wastes from the blood, concentrate
     them, and then add them to undigested food
     before it leaves via the anus
• Terrestrial arthropods may have small excretory
  glands by their legs instead of Malpighian tubules
• Aquatic arthropods dispose of cellular wastes by
  diffusing them from the body into the surrounding
   – Also eliminate nitrogen-containing wastes
     through a pair of green glands located near the
     base of the antennae
      • Are emptied to the outside through a pair of
        openings in the head
The diamond beetle uses
Malpighian tubules to get rid of
nitrogen-containing wastes,
whereas the hermit crab uses its
green glands and gills.
• Have well-developed nervous systems
• All have a brain that consists of a pair of
  ganglia in the head
• Have a nerve cord with several other pairs of
   – Serve as local command centers to
     coordinate the movement of legs and wings
      • Why insects can move after their heads
        are cut off
• Have simple sense organs such as statocysts and
  chemical receptors
• Have compound eyes that contain more than 2000
  separate lenses that can detect color and motion
• Have well-developed sense of taste
   – Receptors located on mouthparts, antennae, and legs
• Insect ears are found in strange places
   – Eardrums are normally located behind their legs
• Sense organs help it detect and escape predators
• Some also have venomous stings and bites
• Some arthropods trick predators by creating a
   – Drop a claw or a leg
      • Body part keeps moving to distract the predator
        while the rest of the animal scurries away
• Use visual trickery to fool predators
• Hide through camouflage
• Others imitate the warning coloration of poisonous or
  dangerous species—mimicry
The Band-Eyed Brown Horsefly
has huge compound eyes

   A harlequin beetle uses its
   long antennae as “feelers.”
   The red hourglass on the
   abdomen of the black widow
   spider warns of the spider’s
   venomous bite.
• Have well-developed muscle systems that are
  coordinated by the nervous system
• Muscle generate force by contracting, then
  transfer that force to the exoskeleton
• At each joint, some muscles are positioned to
  flex the joint and other muscles extend to it
   – Allows arthropods to beat their wings
     against the air to fly, push their legs against
     the ground to walk, or beat their flippers
     against the water to swim
• Reproduction is simple
• Males and females produce sperm and eggs
• Fertilization takes place inside the body of the
• The male uses a special reproductive organ to
  deposit sperm inside the female
• EXCEPTION: In spiders and some
  crustaceans, the male deposits a small packet
  of sperm that the female picks up
   Growth and Development in
• Exoskeletons present a problem in terms of
• Arthropods must replace their exoskeletons
  with larger ones in order to allow their
  bodies to increase in size as they mature
• In order to grow, all arthropods must molt,
  or shed, their exoskeletons
  – Controlled by hormones
    Growth and Development in
• When molting time is near, the epidermis
  digests the inner part of the exoskeleton and
  absorbs much of the chitin
• After its secretes a new exoskeleton inside the
  old one, an arthropod pulls completely out of
  its old skeleton
   – Often eat what is left of the old exoskeleton
   – Must then wait for the new exoskeleton to
       • Can take a few hours to a few days
   Growth and Development in
• Molt several times between hatching and
• In most cases, the process of growth and
  development involves metamorphosis, or a
  dramatic change in form
• As the young grow, they keep molting and
  getting larger until they reach adult size
• Along the way, they gradually acquire the
  characteristics of adults
 Growth and Development in Arthropods
• Many insects undergo complete metamorphosis—a
  four stage process where the eggs of insects hatch into
  larvae that look nothing like their parents
• As they grow, they molt repeatedly
• When it reaches a certain age, it sheds its larval skin
  one last time and becomes a pupa
   – During this stage the insects body is completely
   – After metamorphosis, the animal emerges as a fully
     grown adult with both internal and external body
     parts that are completely different from what it had
     Chapter 28:
         Section 2:
Spiders and Their Relatives
   Spiders and Their Relatives
• Belong to the subphylum Chelicerata
  – Arthropods that are characterized by a
    two-part body and mouthparts called
  – Lack sensory feelers
  – Body is divided into two parts
Spiders and Their Relatives
• Cephalothorax
   –Anterior end contains the brain, eyes,
    mouth and mouthparts, and
   –Posterior end carries the front part of
    the digestive system and several pairs
    of walking legs
• Abdomen
   –Contains most of the internal organs
   Spiders and Their Relatives
• All chelicerates have two pairs of
  appendages attached near the mouth that
  are adapted as mouthparts
   – 1st pair – chelicerae
   – 2nd pair – pedipalps
A jumping spider captures its prey by
pouncing on it, rather than by
catching it in a web
The internal structures of a typical spider
            Horseshoe Crabs
• Among the oldest chelicerates
• Not true crabs
• Appeared in the Ordovician Period (more than
  430 million years ago)
• True “living fossils”
• Heavily armor-plated, have 5 pairs of walking
  legs, and long spike like tails
• Can grow up to 60 cm long
• Newly hatched horseshoe crab larvae are
  called trilobite larvae because they look much
  like their extinct distant relatives
A horseshoe crab’s tiny pincher like
chelicerae and five pairs of walking legs
are visible when the animal is turned on
its back
• Most familiar chelicerates are the
   – Includes spiders, scorpions, ticks, and
   – All adult arachnids have four pairs of
     walking legs on their cephalothorax
   – Many are carnivores and are adapted
     for capturing and holding prey and
     also biting and sucking out soft parts
• Usually feed on insects
• Capture their prey in a variety of ways
   – Ensnare prey in webs
   – Stalk and pounce prey
• Once a spider captures its prey, it uses hollow fanglike
  chelicerae to inject paralyzing venom into it
• When the prey is paralyzed, the spider’s mouth introduces
  enzymes into the wounds
   – Break down the prey’s tissues, enabling the spider to
     suck up the liquefied tissues with it’s esophagus and a
     specialized pumping stomach
• Whether or not they spin webs, all spiders produce a
  strong, flexible protein called silk
   – Silk, which is produced in special glands located
     in the abdomen, is five times stronger than steel
   – Spiders spin silk into webs, cocoons for eggs,
     wrappings for prey, and other structures by
     forcing liquid silk through organs called
      • As the liquid silk is pulled out of the
         spinnerets, it hardens into a single strand
      • The spiders of web-spinning species can build
         intricate webs almost as soon as they hatch –
         without having to learn how
The wolf spider ambushes prey from
its silk-lined burrow. Large tarantulas
are capable of catching and devouring
small vertebrates, such as lizards
             Mites and Ticks
• Small arachnids, many of which are parasites
  on humans, farm animals, and on important
  agricultural plants
• Most are smaller than 1mm
• The chelicerae are needlelike structures that
  are used to pierce the skin on their host
• May also have large teeth to help the parasite
  keep a firm hold on the host
• The pedipalps are often equipped with claws
  for digging in and holding on
             Mites and Ticks
• Some species damage houseplants and are major
  agricultural pests on crops such as cotton
• Others cause painful itching rashes in humans,
  dogs, and other mammals
• A whole host of ticks parasitize humans and the
  animals we raise
• Tick bites are not just annoying, they can be
   – Rocky Mountain spotted fever
   – Lyme disease
Red velvet mites are similar in form
to other members of their class,
However, they are unusual in that they
are not parasites and are relatively large
• Scorpions are widespread in warm areas around
  the world
• All scorpions are carnivores that prey on other
  invertebrates, usually insects
• The pedipalps of scorpions are enormously
  enlarged into a pair of claws
• The abdomen, which is long and segmented,
  terminates in a venomous barb used to sting prey
• Usually, a scorpion grabs prey with its pedipalps,
  then whips its abdomen over its head to sting the
  prey, thus killing or paralyzing it
• Then chews its meal with its chelicerae
• Most North American scorpions have venom
  powerful enough to cause about as much pain
  as a wasp sting
   – However, there are some more harmful
     species of scorpions that have killed small
     children who were stung accidentally
The loser of a fight between two scorpions will be stung
and eaten by the winner. Biologists can locate scorpions
at night by shining UV light on the desert floor. Under UV
light, scorpions glow brightly in the dark.
Chapter 28: Arthropods

   Section 3: Crustaceans
• Subphylum Crustacea contains over 35,000
• Primarily aquatic
• Range in size from microscopic to 6 meters in
• All crustaceans share a number of structural
   – Hard exoskeleton
   – Two pairs of antennae
   – Mouthparts called mandibles
• Main crustacean body parts are the head,
  thorax, and abdomen
• In many crustaceans, the head and thorax have
  fused into a cephalothorax that is covered by a
  tough shell called the carapace
• Many large crustaceans have calcium
  carbonate in the exoskeleton
   – This is what makes the shells of crustaceans
     such as crabs and lobsters hard and stony
• In crustaceans, the first two pairs of appendages are
  “feelers” called antennae
   – Bear many sensory hairs
• The third pair of appendages are mouthparts that are
  called mandibles
   – Short, heavy structures designed for biting and
     grinding food
• The appendages on the thorax and abdomen vary greatly
  from one group of crustaceans to another
   – May be modified for internal fertilization, carrying
     eggs, spearing prey, burrowing, or many other

• The appendages on a crayfish’s thorax and
  abdomen are adapted for several different functions
   – Thorax
      • Pair of large claws
         –Catch prey, pick up, crush, and cut food
      • Four pairs of walking legs
   – Abdomen
      • Swimmerets
         –Used for swimming
      • Paddle-like appendages
• The paddle like appendages and the final
  abdominal segment together form a large, flat
• When the muscles of the abdomen contract,
  the crayfish's tail snaps forward
• This provides a powerful swimming stroke that
  can rapidly pull the animal backward
Pill Bug
Black Tiger Shrimp
Hermit Crab
• Page 621 #1 – 3
  Chapter 28: Arthropods

Section 4: Insects and Their Relatives
     Insects and Their Relatives
• The subphylum Uniramia contains more
  species than all other groups of animals alive
   – Includes centipedes, millipedes, and insects
   – Characterized by one pair of antennae and
     appendages that do not branch
   – Are thought to have evolved on land about
     400 million years ago
   – Inhabit almost every terrestrial habitat on
      Centipedes and Millipedes
• Centipedes and millipedes are many-legged animals
• These two classes of arthropods are quite similar in
   – 3000 species of centipedes
   – 7500 species of millipedes
• Centipedes and millipedes are characterized by a long,
  wormlike body composed of many leg-bearing
• Because they lack closeable spiracles and a waterproof
  coating on their exoskeleton, their bodies lose water easily
• Thus they tend to live beneath rocks, in soil, or in other
  relatively moist areas
• Carnivores
• Have a pair of poison claws in their head region
   – Used to catch and stun or kill prey
• Eat other arthropods, earthworms, toads, small snakes,
  and mice
• Usually about 3 – 6 cm long
• Despite their name, which means 100 legs, centipedes
  may have from 15 to 170 pairs of legs
• Each segment that makes up the body of the centipede
  bears one pair of legs, except for the first segment and
  the last three segments
• Each millipede body segment is formed from the
  fusion of two segments in the embryo and thus
  bears two pairs of legs
• Timid creatures that live in damp places under
  rocks and in decaying logs
• Feed on dead and decaying plant material
• When disturbed, many millipedes roll up into a
  ball to protect their softer undersides
• Some can also defend themselves by secreting
  unpleasant or toxic chemicals
• More than 900,000 insects
  – New ones are discovered in the tropics all the time
  – Extremely varied in body shape and habits
  – Insects are characterized by a body that is
    divided into three parts – head, thorax, and
    abdomen – and has three pairs of legs attached
    to the thorax
  – A typical insect has one pair of antennae and one
    pair of compound eyes on the head, two pairs of
    wings on the thorax, and uses a system of tracheal
    tubes for respiration
• Insects get their name from the Latin word
  insectum, meaning notched, which refers to the
  division of their body into three main parts
• The essential life functions in insects are
  carried out in basically the same ways as they
  are in other arthropods
• However, insects show a variety of interesting
  adaptations in feeding, movement, and
• Three pairs of appendages that are used as
• Can take on an enormous variety of shapes in
  species adapted to feed on different foods
• Insect adaptations for feeding are not restricted
  to the shapes of the mouthparts
• Many insects produce saliva that contains
  digestive enzymes and helps break down food
• Insects have three pairs of walking legs
   – Often equipped with spines and hooks for holding onto
      things and for defense
   – May be adapted for functions such as jumping or
      capturing and holding prey
• Along with birds and bats, insects are the only living
  organisms that are capable of unassisted flight
• The flying ability of insects varies greatly
• In flying insects, most of the space in the thorax is taken
  up by the large muscles that operate the wings
             Insect Societies
• Many animals form colonies, which are
  collections of individuals of the same species
  that live together
• Several types of insects are unique among
  invertebrates in that they form a special type of
  colony known as a society
   – Separate individuals are dependent on one
     another for survival
      • Social insects
             Insect Societies
• These insects have developed complicated
  societies that may be composed of from half a
  dozen to more than 7 million individuals
• Within such societies there is division of labor
   – Different individuals perform the tasks
     necessary for the survival of the entire group
   – There are several types of individuals within
     insect societies
               Insect Societies
• The basic types are:
   – Reproductive females
      • Queens
      • Lay eggs that hatch into new individuals for the
      • Largest individual in the colony
   – Reproductive males
      • Fertilize the queen’s eggs
   – Workers
      • Perform all the colony’s tasks except for
       Insect Communication
• All insects use sound, visual, chemical,and
  other types of signals for communication
• Much of the communication done by
  nonsocial insects involves finding a mate
• Insects release chemical messengers called
  pheromones that affects the behavior
  and/or development of other individuals of
  the same species
          Insect Communication
• Communication in social insects is generally more complex
  than in nonsocial insects
• A sophisticated system of communication is necessary to
  organize a society
• Each species of social insect has its own “language” of
  visual, touch, sound, and chemical signals that convey
  information among members of the colony
• Pheromones are particularly important in insect societies
   – Short-term messages
   – Long-term controls
• Also use “dances” to convey information
   – Round dance
   – Waggle dance
 Chapter 28: Arthropods

Section 5: How Arthropods Fit into
            the World
    How Arthropods Fit into the
• Arthropods play many roles in the natural world
   – Direct food source for carnivorous organisms
   – Two-thirds of the world’s flowering plants depend on
     insects to pollinate them
   – Agriculture would be impossible without the bees,
     butterflies, wasps, moths,and flies that pollinate crops
   – Bees manufacture honey
   – Silkworms produce silk
   – Shrimp, crab, crayfish, and lobster are a large food
     source for humans
   – Many useful chemicals can be obtained from
    How Arthropods Fit into the
• Not all arthropods are beneficial to humans
  – Insects and arachnids cause billions of dollars in
    damage each year to livestock and crops around the
  – Mosquitoes inflict annoying bites, and some
    species carry malaria and yellow fever
  – Termites cause extensive damage to wooden
  – Farmers have spent billions of dollars on poisonous
    chemicals to save their crops from these pests

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