Chapter 28 - Arthropods

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Biology - Chapter 28Arthropods
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Introduction to Arthropods

• Phylum Arthropoda - vary enormously in size,
  shape, and habits

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Crustaceans

• Crustacea- over 35,000 species, mainly aquatic
• tiny as a water flea (0.25 mm) to Japanese spider
  crabs (6 meter)
• characterized by a hard exoskeleton 2 pairs of
  antennae mouthparts called mandibles

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Introduction to Arthropods

• Although there are many different types of
  arthropods, they all have four important
  arthropod features
• Tough exoskeleton shed to allow for growth
  (molt)
• Protection
• Prevent water loss
• Made up of chitin (protein)
• 2. Series of jointed appendages in pairs
• 3. Segmented body head, thorax, abdomen

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Introduction to Arthropods

• Well developed nervous system
• -- sense organs eyes, touch, hearing
• brain, located in dorsal part of head
• open circulatory system, powered by a single
  heart
• Flows into open cavities called sinuses

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Introduction to Arthropods

• Development through Metamorphosis
• 1. Incomplete metamorphosis eggs hatch to nymph
  (kid) to adult
• examples grasshoppers and crickets

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Spiders and their Relatives

• also lack sensory feelers found on the heads of
  most other arthropods
• the two-part body is
• 1. Cephalothorax
• 2. Abdomen

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Introduction to Arthropods

• 2. Complete metamorphosis involves four stages
• a) the egg
• b) larvae (a wormlike stage that does not look
  like the adults)
• c) pupa (an inactive stage that totally
  rearranges the body)
• d) the adult
• Moths, butterflies, flies, lady bugs

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Introduction to Arthropods

• Phylum Arthropods is subdivided into three
  subphyla
• 1. Subphylum Chelicerata
• Includes spiders, ticks, mites, scorpions, and
  horseshoe crabs

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Spiders and their Relatives

• Cephalothorax- contains the brain, eyes, mouth
  and mouthparts, and esophagus
• Abdomen- contains most of the internal organs

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Spiders and their Relatives

• All chelicerates have two pairs of appendages
  attached near the mouth that are adapted as
  mouthparts
• first pair are chelicerae
• second pair is longer, and called pedipalps
• both serve different feeding job

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Spiders and their Relatives

• Among the oldest chelicerates are the horseshoe
  crabs

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Spiders and their Relatives

• Scorpions- carnivores that prey on other
  invertebrates, usually insects
• pedipalps are enormously enlarged into a pair of
  claws
• abdomen is long and segmented ends in a venomous
  barb to sting prey

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Introduction to Arthropods3 Subphylums

• 1. Subphylum Crustacea
• includes crabs, shrimp, crayfish

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Crustaceans

• Main body parts are the head, thorax, and abdomen
• in many, the head and thorax have fused
  cephalothorax, many (crabs, lobsters)

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Introduction to Arthropods

• 3. Subphylum Uniramia includes most arthropods
  centipedes, millipedes, and all insects (bees,
  moths, flies, grasshoppers, beetles)

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Insects Anatomy

• Head
• Antennae (sensory appendages)
• Mouthparts
• Compound eye
• Thorax
• 3 pairs of legs
• Wings?
• Abdomen

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Insects and their Relatives

• Subphylum Uniramia- more species than all other
  groups of animals alive today!
• 1. Class Insecta flies, bees, butterflies,
  dragonflies, grasshoppers, lice, mosquitos
• 2. Class Chilopoda centipedes
• 3. Class Diploda -- millipedes

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Section 28-2Spiders and their Relatives

• Have 4 pairs of walking legs
• long spike-like tails
• can grow up to 60 cm long, about the size and
  shape of a frying pan
• newly hatched are called trilobite larvae because
  they look so much like them

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Section 28-2Spiders and their Relatives

• Class Arachnida- includes spiders, ticks,
  scorpions, and mites
• have 4 pairs of walking legs
• pedipalps capture and hold prey chelicerae
  adapted for biting and sucking out soft parts

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Section 28-2Spiders and their Relatives

• Spiders- predators that usually feed on insects
• capture prey in a variety of ways
• ensnare in a web
• stalk, and then pounce
• ambush under camouflage, then leap out and grab

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Section 28-2Spiders and their Relatives

• Once captured
• 1. Hollow fanglike chelicerae inject paralyzing
  venom
• 2. Mouth introduces enzymes
• 3. Enzymes break down tissue
• 4. Spider sucks up the liquefied tissues with
  esophagus and specialized pumping stomach

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Section 28-2Spiders and their Relatives

• Whether or not they spin webs, all spiders
  produce a strong, flexible protein called silk
• produced in special glands in the abdomen
• is 5 times stronger than steel
• makes webs, cocoons for eggs, or wrappings for
  prey

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Section 28-2Spiders and their Relatives

• Forces the liquid silk through organs called
  spinnerets
• it then hardens into a single strand
• do not have to learn how to spin the intricate
  webs it is programmed into their brain as soon
  as they hatch

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Section 28-2Spiders and their Relatives

• Mites and Ticks- small arachnids, many of which
  are parasites
• the chelicerae are needlelike structures that are
  used to pierce the skin of their hosts
• the chelicerae also have large teeth to help the
  parasite hold on to the host

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Section 28-2Spiders and their Relatives

• Some, such as spider mites,are major agricultural
  pests
• others, such as chiggers, mange and scabies
  mites,cause painful itching rashes in humans
• tick bites are not just annoying they may also
  spread Rocky Mountain spotted fever and Lyme
  disease

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Section 28-2Spiders and their Relatives

• Scorpion grabs the prey with its pedipalps then
  whips the abdomen over its head to sting the
  prey- thus killing or paralyzing it
• they like to crawl in moist, dark places- good
  idea to check your shoes when putting them on!

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Section 28-3Crustaceans

• OBJECTIVES
• Discuss the distinguishing characteristics of
  crustaceans.

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Section 28-3Crustaceans

• OBJECTIVES
• Describe the anatomy of a typical crustacean.

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Section 28-3Crustaceans

• In crustaceans, the first two pairs of appendages
  are feelers called antennae, which bear many
  sensory hairs
• third pair of appendages are mouthparts called
  mandibles
• might bite and grind filter feeding

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Section 28-3Crustaceans

• Appendages can vary greatly
• barnacles have delicate, feathery appendages for
  filter feeding
• others have legs for walking or swimming
• some modified for fertilization, carrying eggs,
  spearing prey

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Section 28-3Crustaceans

• Appendages are adapted for
• the large claws catch prey pick up, crush, and
  cut food- these are on the thorax
• 4 pairs of walking legs, also on the thorax
• Flipper-like swimmerets for swimming on the
  abdomen

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Section 28-3Crustaceans

• The paddle-like appendages and the final
  abdominal segment form a large, flat tail
• very powerful a crayfish can snap forward, thus
  rapidly pulling the animal backwards
• roly-poly in Figure 28-22, page 620- pill bug
  (a crustacean)

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Section 28-4Insects and their Relatives

• OBJECTIVES
• Describe and give examples of three classes in
  the subphylum Uniramia.

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Section 28-4Insects and their Relatives

• OBJECTIVES
• Discuss the anatomy of a typical insect.

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Section 28-4Insects and their Relatives

• OBJECTIVES
• Explain how insects communicate.

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Section 28-4Insects and their Relatives

• They lack closable spiracles and a waterproof
  coating on their exoskeleton
• thus they lose water easily
• therefore, they tend to live beneath rocks, in
  soil, or in other relatively moist areas

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Section 28-4Insects and their Relatives

• Class Chilopoda- centipedes
• these are carnivores that have in addition to
  their mouthparts, a pair of poison claws in their
  head region
• used to catch and stun or kill prey- other
  arthropods, earthworms, toads, small snakes, and
  even mice

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Section 28-4Insects and their Relatives

• Most centipedes in North America are 3-6 cm long
  but some tropical species are brightly colored,
  and up to 26 cm
• Despite the name (which means 100 legs), they can
  have a variable number, depending upon how long
  they are

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Section 28-4Insects and their Relatives

• There is only one pair of legs per body segment
• except the mouth, which has the poison claws, and
  the last three segments (which are legless)

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Section 28-4Insects and their Relatives

• Class Diplopoda- these are the millipedes, and
  they do not have a thousand legs like the name
  implies
• they have 2 pairs of legs per body segment
• these are timid creatures, and are detritus
  feeders

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Section 28-4Insects and their Relatives

• Class Insecta- the insects have more than 900,000
  species new ones are being discovered in the
  tropics all the time
• 3 out of every 4 animals!
• three part body head, thorax, and abdomen.
  There are 3 pairs of legs on the thorax

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Section 28-4Insects and their Relatives

• A typical insect has one pair of antennae, one
  pair of compound eyes on the head, two pairs of
  wings on the thorax, and uses a system of
  tracheal tubes for respiration
• Figure 28-26, page 623

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Section 28-4Insects and their Relatives

• Insects get their name from the Latin word
  insectum, meaning notched- refers to the division
  of their body into the three parts
• many insects, such as ants, have clear cut
  divisions- others such as grasshopper may not
  have body parts sharply defined

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Section 28-4Insects and their Relatives

• Feeding- insects have 3 pairs of appendages that
  are used as mouthparts, including a pair of
  mandibles (jaws)
• many shapes and varieties
• grasshopper cut / chew plants
• mosquito tube pierces skin to suck blood
  (females only)

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Section 28-4Insects and their Relatives

• butterfly long tube for sipping nectar
• bee chewing and gathering nectar
• fly spongy mouthpart used to soak up food

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Section 28-4Insects and their Relatives

• The saliva of female mosquitoes, which is
  injected when the mosquito bites, contains
  chemicals that prevent blood from clotting- also
  has chemicals that cause the itching
• bee body covered with many hairs that collect
  pollen

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Section 28-4Insects and their Relatives

• Chemicals in bee saliva help change nectar into a
  more digestible form- honey
• glands on the bee abdomen secrete wax, which is
  used to build storage chambers for food and
  others structures within a beehive

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Section 28-4Insects and their Relatives

• Movement- insects have 3 pairs of walking legs
• often equipped with spines or hooks for holding
  on, or used for defense
• may be used for jumping (fleas), or holding prey
  (praying mantis)

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Section 28-4Insects and their Relatives

• Movement- along with birds and bats, insects are
  the only living organisms capable of unassisted
  flight
• flight ability varies greatly from slow
  butterflies to fast flies, bees, and dragonflies
• requires enormous energy, thus have oversized
  mitochondria

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Section 28-4Insects and their Relatives

• Insect societies- many animals form colonies,
  collections of individuals of the same species
• several types of insects for a special colony
  called a society
• separate individuals are dependent upon one
  another for survival

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Section 28-4Insects and their Relatives

• Insect societies- examples are termites, wasps,
  bees, and ants
• all called social insects
• they have a division of labor
• 1) reproductive females
• 2) reproductive males
• 3) workers

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Section 28-4Insects and their Relatives

• Reproductive females queen, typically there is
  only one, and usually the largest individual in
  the colony- page 625
• termite queen may be 14 cm long, 10 times normal
• can produce more than 30,000 eggs a day!

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Section 28-4Insects and their Relatives

• The reproductive males function only to fertilize
  the queens eggs
• queen bee mates only once
• the successful males die after mating, and the
  unsuccessful males are ejected from the colony
  and soon perish (since they are no longer needed!)

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Section 28-4Insects and their Relatives

• The workers perform all colony tasks except
  reproduction
• care for queen and eggs gather and store food
  build and maintain the colonys home
• in bees, the workers are sterile females in
  termites, the workers consist of males and females

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Section 28-4Insects and their Relatives

• Insect communication- may use sounds, visual,
  chemical, or other methods
• may be necessary to find mate
• male crickets chirp by rubbing their forewings
  together
• male cicadas buzz special membranes on their
  abdomen

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Section 28-4Insects and their Relatives

• Male fireflies turn a light producing organ in
  their abdomen on and off
• many insects can release chemicals that attract
  the opposite sex- called pheromones
• communication in non-social insects not near as
  complex

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Section 28-4Insects and their Relatives

• Queen bee produces a pheromone, called queen
  substance, that prevents the development of rival
  queens
• this substance makes the worker bees unable to
  lay eggs
• need a new queen? Feed the larvae a special diet

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Section 28-4Insects and their Relatives

• Honeybees communicate with sound and movement, as
  well as with pheromones
• worker bees are able to convey information about
  the type, quality, direction, and distance of
  food by dancing
• Austrian biologist Karl von Frisch

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Section 28-4Insects and their Relatives

• 1. Round dance- bee that has found food will
  circle first one way, then the other, over and
  over again (Fig. 28-32, p.627)
• tells others that food is within 50 meters, but
  not direction
• frequency of dance conveys quality of the food

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Section 28-4Insects and their Relatives

• 2. Waggle dance- the bee that has found food runs
  forward in a straight line while wiggling her
  abdomen, then circles around much like a figure
  eight
• food is more then 50 m away
• the direction of the dance tells the direction of
  the food source

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Section 28-5 How Arthropods Fit Into the World

• OBJECTIVES
• Describe how arthropods interact with other
  organisms in nature.

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Section 28-5 How Arthropods Fit Into the World

• OBJECTIVES
• Discuss how arthropods affect humans.

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Section 28-5 How Arthropods Fit Into the World

• Such a large diverse group will play many roles
  in the natural world
• can be a direct source of food for many organisms
• either eating others or being eaten by them

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Section 28-5 How Arthropods Fit Into the World

• Involved in symbiotic relationships Fig. 28-34,
  p.629
• pores of our skin are home to thousands of
  harmless microscopic mites no matter how much we
  clean our home, even our beds, there are millions
  of these dust mites

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Section 28-5 How Arthropods Fit Into the World

• Agriculture would be impossible if not for bees,
  butterflies, wasps, moths, and flies that
  pollinate
• honey from bees silk from silkworm moths
• shrimp, crab, crayfish, lobster used as a food
  source for humans

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Section 28-5 How Arthropods Fit Into the World

• Grasshoppers and termites can also be eaten they
  can also do considerable damage to crops and wood
  materials
• many insects and spiders are predators on other
  harmful species

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Section 28-5 How Arthropods Fit Into the World

• Chemicals from arthropods
• extract of horseshoe crab blood is used to test
  purity of medications
• chitin from exoskeletons used to dress wounds and
  make thread for surgical stitches

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Section 28-5 How Arthropods Fit Into the World

• The chitin may also be sprayed on fruit and
  frozen food to prevent spoilage
• the adhesive that barnacles use to attach
  themselves to rocks under water could be used in
  dentistry or underwater construction

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Section 28-5 How Arthropods Fit Into the World

• Spider venom is being tested as a pesticide
• spider silk that could be used in making
  aircraft, helmets, bulletproof vests, and
  surgical thread

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Section 28-5 How Arthropods Fit Into the World

• However good they are, they can also do
  considerable damage
• parasites damage livestock and crops
• mosquitoes annoying bites and the spread of
  malaria and yellow fever

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Section 28-5 How Arthropods Fit Into the World

• Biting flies carry diseases such as sleeping
  sickness and river blindness
• fleas carrying bubonic plague
• termites damaging wood
• locusts (grasshoppers) destroying crops