The Arthropods

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The Arthropods

• Chapter 33

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General statistics

• Most numerous and successful phyla
• 400,000 known plant species
• 250,000 known non-arthropod animals
• Over 1,000,000 species of arthropods.

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5 classes of arthropods
diplopoda
crustacea
chilopoda
Insecta
arachnida
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General characteristics

• Arthropoda
• From the Greek word arthron meaning joint and
  poda meaning foot
• 1) Jointed appendages used for crawling,
  swimming, flying, etc.

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More characteristics

• 2. Possess an exoskeleton
• Made up of protein and chitin
• Helps to waterproof and prevent water loss
• Main disadvantage exoskeleton does not grow
  with the organism. Must be shed.
• molting

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• 3. Segmented body
• 4. Well developed nervous systems
• 5. Open circulatory system

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Class Crustacea

• Lobsters, crayfish, crabs, shrimp.
• Mostly marine, some fresh water.
• All have 2 pairs of antennae on the head and 2
  body regions.

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The crayfish

• Cephalothorax fusion of the head and thorax
• Antennules first pair of appendages attached to
  the head. Shorter of the two pairs of antennae
• Used for touch, taste, and balance

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More appendages

• 2nd pair antennae (long) used for touch and
  tasting
• Mandibles (jaws) 1 pair. Used for crushing food
• Maxillae 2 pairs. Used to handle food
• Maxillipeds 3 pairs. Touch, taste, handling of
  food

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Chelipeds

• Large first legs where claws are found.
• Used for defense and grasping prey.

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and more appendages

• Walking legs (4 pairs)
• Swimmerets appendages found on the underside of
  the abdomen.
• Used for swimming and carrying eggs and young.

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Internal Structure

• NUTRITION
• Food is caught with the chelipeds, crushed by the
  mandibles and passed into esophagus.
• Food then digested and wastes passed out the anus.

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Excretion

• Wastes from the blood are removed by the green
  glands in the head.

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Circulation and respiration

• Possess a dorsal heart.
• Open circulatory system (no capillaries nor
  veins)
• Arteries dump blood into open spaces, sternal
  sinus collects old blood and channels it to gills
  to pick up oxygen.

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• Hemocyanin copper containing pigment in the
  blood that aids in transport of oxygen.
• Gasses are exchanged at gills

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Nervous system

• Well developed sensory organs
• Compound eyes, many sensory hairs
• Statocysts sacs at the base of the antennules
  that aids in balance.

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Reproduction

• Separate sexes. Can determine sex by looking at
  first pair of swimmerets.
• Male will have enlarged first pair of swimmerets
  to transfer sperm to seminal receptacle of female
  during the fall.
• Eggs attach to swimmerets and hatch in the
  spring.
• Young stay attached until self sufficient.

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Baby crayfish
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Class Chilopoda (centipedes)

• centipede literally means 100 feet
• Usually 30 to 60 legs, can be as many as 350 legs
• A distinct 6 segmented head
• Worm-like body with similar segments.

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More centipede facts

• All body segments have one pair of legs except
  the one behind the head and the last two. Fairly
  fast crawlers
• Feed on insects using poison claws.
• Usually found in dark damp places
• Under logs and rocks, in basements

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Class diplopoda (millipedes)

• Literally 1000 legs although no species has this
  many legs. World record is 750 legs.
• Usually anywhere from 100 to 300 legs.
• Two pairs of legs per body segment except for the
  last two segments. Slow moving
• No poison claws feed on decaying plant material.

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Class arachnida

• Spiders, scorpions, ticks, and mites
• Mostly free-living. A few parasitic
• Some are harmful to humans (poisonous cause
  disease)
• Mostly helpful
• Get rid of pests like mosquitos

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Ticks

• Can cause disease ex.
• Spotted Rocky Mt. Fever
• Lyme Disease

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Lyme Disease

• Carried by deer ticks. Caused by a bacterium.
• Usually in wooded areas of Mid-Atlantic states
  and New England.

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spiders

• 2 body segments
• Cephalothorax (6 pairs of appendages)
• Adbdomen
• No antennae or
• Chewing jaws

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chelicerae

• First pair of appendages
• Also known as the fangs of a spider
• Will inject a poison into its prey.

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pedipalps

• Found between the first pair of legs and the
  chelicerae.
• Used for sensing chemicals and touch
• Used to manipulate food.

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Abdomen appendages

• 4 pairs of walking legs
• Book lungs respiratory organs on underside of
  abdomen
• Spinnerets posterior end of abdomen, used to
  make silk for webs and raising and lowering
  themselves.

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Class insecta

• Most successful class of arthropods
• 30 orders
• Live in all habitats
• High reproductive rates (all reproduce sexually)
• Small in size
• Only invertebrates capable of flight

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Why is flight such an advantage?

• Escape form enemies
• Search for food
• Allow insects to inhabit environments not
  inhabited by other organisms.
• Less competition for natural resources.

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3 body regions

• Head (mouthparts, antennae, eyes)
• Thorax (3 pairs of legs, wings)
• Abdomen (respiratory structures)

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Specialized structures

• Mouthparts
• 2 main types

sucking
chewing
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legs

• Used for swimming, collecting pollen. Defense,
  grasping prey, jumping

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Incomplete metamorphosis

• Series of changes where an insect grows from eggs
  to a nymph to an adult
• Nymph immature form that closely resembles the
  adult form except for certain features.
• Examples grasshoppers, crickets

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Complete metamorphosis

• 4 stages
• Eggs, larva, pupa, adult
• Larval stage examples caterpillars, maggots
• Pupa cocoon
• Changes are controlled by hormones.
• ex.

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Grasshopper (order Orthroptera)

• Head
• 2 large compound eyes
• 3 simple eyes
• 1 pair of antennae
• Mouthparts located outside the mouth(mandible,
  maxilla, special tongue-like organ)

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Thorax

• 3 separate segments to the thorax with each
  possessing a pair of legs
• Each leg has five segments ending in a clawed
  tarsus or foot
• 1st and 2nd pairs of legs are for crawling.
• Last pair used for jumping
• 2 pairs of wings

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Abdomen

• Made up of 10 segments
• Each segment has one pair of spiracles (openings
  into air tubes)
• 1 pair of tympanum (hearing organs)
• reproductive organs

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Female abdomen

• Ovipositor hard four pointed organ at the base
  of the abdomen used to dig holes for burying eggs.

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Harmful effects of insects

• Cause millions of dollars in crop damage.
• examples
• Corn smut, rootworm, locusts, tent caterpillars

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Images
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Transmit diseases

• Malaria transmitted by mosquitoes
• West Nile virus also mosquitoes
• West Nile link

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Destroy property

• Cockroachestermites moths

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Economic value of insects

• Help pollinate fruit trees
• Produce honey
• Kill other harmful insects
• Eat dead plant and animal material

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Ways to kill insects

• Most common insecticides
• Trap and sterilize males
• Genetic engineering
• Bt corn

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Phylum Echinodermata

• Literally means spiny-skinned
• All marine
• Examples

starfish
sea urchin
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characteristics

• Well developed coelom
• Endoskeleton
• Simplest organism showing embryological formation
  of the anus before formation of the mouth.
• Radial symmetry

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starfish

• Usually five arms but can possess up to 20 arms
• Extensive water-vascular system
• Water will enter through the sieve plate and pass
  through a series of canals into each arm.

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Tube feet

• Small water filled tubes or projections on the
  ventral surface used for locomotion, respiration,
  grabbing prey, and digestion.

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More starfish facts

• Feed on clams and oysters
• Skin gills small finger-like appendages on the
  surface of starfish that is a site for
  respiration
• Separate sexes
• Can regenerate lost arms. An entire new starfish
  can grow as long as part of the central disk is
  present.

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Assignment

• Page 730
• 1-17,20,21,22,25,26,27,30,32