Arthropods

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Arthropods
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What are ARTHROPODS?

• Coelomate
• Segmented
• Bilateral Symmetry
• Exoskeleton made of protein and chitin
• Jointed appendages any structure (leg or
  antennae) that grows out of the body

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What are Arthropods?

• earliest invertebrates to exhibit jointed
  appendages
• Jointed appendages are an advantage because they
  allow more flexibility for animals with hard,
  rigid exoskeletons
• Joints allow powerful movements and allow
  appendages to be used in many ways

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What are Arthropods?
Appendages Jointed Appendages
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Exoskeletons Provide Protection

• made up of protein and CHITIN
• can be a continuous
• covering over most
• of body OR
• made of plates
• that are held
• together by hinges

Continuous
Hinged
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Exoskeleton Advantages

• Protects, supports internal tissues
• Provides place for muscle attachment
• Aquatic arthropods have exoskeleton reinforced
  with calcium carbonate

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Exoskeleton Disadvantages

• Heavy
• the larger the animal, the thicker and heavier
  the exoskeleton
• Exoskeletons dont grow
• animals must molt when they get too large for
  exoskeleton

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Molting

• Animal contracts muscles and takes in air or
  water
• Body swells and causes exoskeleton to split open,
  usually along the back

• Most arthropods will molt 4-7 times before
  becoming an adult.

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Before the new exoskeleton hardens...

• increased circulation to all parts of the body
  cause the animal to puff up and new exoskeleton
  hardens leaving some growing room
• animal cant protect itself, cant move

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Question 1

• Which of the following organisms would be
  most likely to have an exoskeleton reinforced
  with calcium carbonate?
• Spider
• Beetle
• Crab
• Dragonfly

Correct!
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Question 2

• Exoskeletons are heavy. Why can aquatic
  arthropods grow so much larger than terrestrial
  arthropods?

The buoyancy of the water helps support the
weight of the exoskeleton
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Question 3

• What is one advantage and one disadvantage of
  flying arthropods having a thinner, lighter
  weight exoskeleton?

Disadvantage less protection Advantage greater
freedom to fly and jump
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Question 4

• What is one advantage and one disadvantage of
  having a cephalothorax?

Disadvantage less flexibility,
mobility Advantage more protection
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Segmentation

• 3 segments
• abdomen
• thorax
• head

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Segmentation

• Sometimes these segments can be fused together
• some have head and fused thorax and abdomen
• some have abdomen
• and fused head and
• thorax (cephalothorax)

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Respiration

• Efficient respiratory systems to meet large O2
  demands
• Large O2 demand needed to sustain high
  metabolism for fast movements
• 3 types of respiratory structures
• gills (aquatic arthropods)
• tracheal tubes (terrestrial arthropods)
• book lungs (terrestrial arthropods)

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Respiration

• Gills
• water moves over gills
• O2 from water diffuses
• into gills and into
• bloodstream
• CO2 from body diffuses out through gills into
  surrounding water

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Respiration

• Tracheal tubes
• branching network of hollow air passages that
  take air throughout the body

Muscle movement brings air in/out through
SPIRACLES (openings in abdomen and thorax)
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Respiration

• Book lungs
• spiders and relatives
• air filled chambers with leaf-like plates
• stacked plates
• are arranged
• like pages
• of a book

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Antennae

• Acute sensing by antennae
• stalk like structure that can detect changes in
  the environment
• movement
• sound
• chemicals
• Used for sound and odor communication

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Eyes

• Compound Eyes
• visual structure with
• many lenses
• Simple Eyes
• visual structure with one lens for detecting
  light
• one pair of compound eyes and 3-8 simple eyes

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Nervous System

• Double ventral nerve cord
• Anterior brain
• Several fused ganglia that control the body
  section they are located in

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Circulatory System

• Open circulatory system
• blood flows away from the heart in vessels
• blood flows out of vessels into tissues
• blood returns to the heart through open spaces

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Digestive System

• Complete digestive system with mouth, intestine,
  and anus
• Mouth has 1 pair of jaws called MANDIBLES
• adapted for holding, chewing, sucking, or biting

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Reproduction Sexual and Asexual

• Sexual reproduction
• separate sexes
• internal fertilization for terrestrial species
• external fertilization for aquatic species

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Reproduction Sexual and Asexual

• Asexual reproduction
• PARTHENOGENISIS
• a new individual develops from an unfertilized
  egg
• seen with ants, aphids and bees

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Arachnids

• spiders (largest group), ticks, mites, and
  scorpions
• 2 body regions cephalothorax and abdomen
• 6 pairs of jointed appendages 12 total
  appendages!

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Arachnids

• 1st pair - chelicerae, are near the mouth
• modified into pincers (hold food) or fangs
  (inject poison)

chelicerae
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Arachnids

• 2nd pair pedipalps, for handling food and
  sensing

pedipalps
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Arachnids

• Silk, for webs, is secreted by silk glands in the
  abdomen
• as it is secreted, it is spun into thread by
  SPINNERETTES
• spiders are predatory and feed almost exclusively
  on other animals

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Arachnids

• Ticks and mites have only 1 body section
• Head, thorax and abdomen are completely fused
• Ticks feed on blood of other animals

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Arachnids

• Mites feed on fungi, plants, and animals
• small not usually visible
• can transmit diseases

Dust mites
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Arachnids

• Scorpions have many abdominal body segments
• Enlarged pincers
• Long tail with
• venomous stinger
• at the tip

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Crustaceans

• crabs, lobster, shrimp, crayfish, barnacles
• Only arthropods with 2 pairs of antennae
• mandibles move
• from side to side
• 2 compound
• eyes

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Crustaceans

• 5 pairs of walking legs
• 1st pair are claws for defense

claw
legs
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Crustaceans

• Most are aquatic and use gills
• pill bugs (roly-polies) live on land, but must
  have moisture to aid in gas exchange

Yes! This is a crustacean!
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Centipedes and Millipedes

• Centipedes are carnivorous eat soil arthropods,
  snails, slugs,
• and worms
• Bites can be painful
• Millipedes eats plants and dead material on
  damp forest floors
• Does not bite, but does
• spray foul-smelling fluid

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Horseshoe Crabs

• Class Merostomata
• Living Fossils- unchanged for 220 million years
  (Triassic period)
• Extensive exoskeleton
• Live in deep coastal waters
• forage bottoms for algae,
• annelids and molluscs

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Insecta

• Flies, grasshoppers, lice, butterflies, beetles
• 3 body segments
• 6 legs
• Very diverse - more insects than all other
  classes of animals combined

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Insecta

• mate once in lifetime
• internal fertilization
• some exhibit
• parthenogenesis
• large number of eggs
• to increase survival rate

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Insecta

• insect embryos develop inside eggs, eggs hatch
• some look like miniature adults
• will molt several times until adult size

Molt
Nymph
Eggs
Nymph
Molt
Adult
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Insecta

• INCOMPLETE METAMORPHOSIS
• 3 stages egg, nymph, adult

• Nymphs cant reproduce
• Nymph gradually becomes an adult

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Insecta

• Some undergo COMPLETE METAMORPHOSIS
• 4 stages egg, larva, pupa, adult
• Metamorphosis is controlled by chemical
  substances in the insect

Egg
Adult
Larva
Pupa
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Insecta

• Incomplete metamorphosis grasshoppers and
  cockroaches
• Complete metamorphosis ants, beetles, flies,
  wasps

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Origins of Arthropods

• Successful because of
• varied life styles
• high reproductive output
• structural adaptations
• hard exoskeletons
• jointed appendages

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Origins of Arthropods

• Hard exoskeletons fossilize a lot is known
  about evolutionary history
• Evolved from ANNELIDS (segmented worms)
• Arthropods have more complex segments, more
  developed nervous systems
• circular muscles in annelids do not exist in
  arthropods

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Question 5

• Spiders are
• predators
• scavengers
• decomposers
• parasites

Predators!
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Question 6

• Having 2 pairs of antennae distinguish _________
  from other arthropods.
• centipedes
• millipedes
• crustaceans
• horseshoe crabs

Crustaceans!
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Question 7

• Why are horseshoe crabs called living fossils?

They remain unchanged after 220 million years!