Chapter 36 Arthropods & Chapter 37 Insects

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Chapter 36 Arthropods Chapter 37 Insects

• The real rulers of the Earth

Sources used include textbook, (Holt Modern
Biology) http//www.ucmp.berkeley.edu/arthropoda
/arthropoda.html
http//evolution.berkeley.edu/evolibrary/article/_
0_0/arthropods_intro_01
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Just how dominant are arthropods?

• More than 83 of all described animal species are
  arthropods.
• That's about 160 million insects for each person
  on Earth.
• Have evolved to fill a variety of ecological
  niches from tiny internal parasite to giant
  bird-eating predator.

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• Arthropods are a lot more than just delicious
  feasts and disgusting pests.
• What are the characteristics of an arthropod ?

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5 Characteristics of all Arthropods
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Bilateral symmetry

• High degree of Cephalization
• Variety of segmented appendages around the mouth
• Segmented antennae- sense environment
• Compound eyes- made of many individual light
  detectors, each with their own lens.

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Segmented Body

• Each body segment tends to repeat the same suite
  of structures (ie, a pair of legs, a set of
  breathing organs, a set of nerves),
• sets of segments are grouped into a larger unit,
  such as the abdomen cephalothorax.

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Hard Exoskeleton

• Made of protein Chitin (a polysaccharide)
• Must molt many times as grows
• Enzymes digest the layer of exoskeleton inside
  soften then
• shed. It takes a few
• days for the newly
• excreted exoskeleton
• to harden.

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Jointed Legs

• How can an animal with a rigid body covering move
  its legs? a problem for arthropods flexibility.
• All arthropods (arthro joint, pod foot) have
  jointed limbs.
• In most of the leg, the exoskeleton is hard, but
  at the joints it is softer and bendable, allowing
  movement in the same way that a suit of armor
  does.
• The limb can be controlled by contracting muscles
  connected to the exoskeleton on both sides of the
  joint.

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Many pairs of limbs

• ancestral arthropod had many body segments with
  one pair of limbs on each segment.
• in modern arthropods,
• some limbs have even been lost completely as they
  evolved to be smaller and smaller, while others
  have evolved into new shapes. functions.
• Tagma-specialized segements

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Systems in Arthropods

• All- Open circulatory system
• Respiration-
• gills (aquatic crustaceans)
• tracheae
• book lungs (spiders)
• Excretion-
• Green glands (Crusteaceans)
• Malpighian tubules(spiders)
• Many arthropods have wings.
• The two major types of mouthparts are
• mandibles, which are jawlike
• chelicerae (singular, chelicera), which are
  pincerlike

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The five major subphyla of the phylum Arthropoda.
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• Arthropods usually divided into 5 subphyla based
  on
• differences in development
• in the structure of appendages, such as
  mouthparts.

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Trilobites

• Extinct
• Many body appendages with one pair of appendages
  per segment
• Trilobites, living in shallow seas, flourished as
  swimmers, crawlers and burrowers for some 350
  million years. They evolved rapidly into many
  beautiful, bizarre and, even by today's
  standards, futuristic forms.
• Fossil evidence of these extraordinary marine
  creatures are found on all continents, entrapped
  in the hardened sediments of Ancient Seas.

http//www.trilobite.com/
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Subphylum Myriapoda

• Meansmany feet
• One pair of branched antennae
• Many body segments
• Includes class
• Diplopoda (millipedes)
• Up to 100 body segments
• 2 pairs of legs on each segment
• Chilopoda (centipedes)
• In tropical regions can reach 12 inches long
• From 15 to 175 pairs of legs

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Subphylum Crustacea

• contains about 38,000 known species.
• Terrestrial Marine
• so diverse their single defining characteristic
  is having two pairs of antennae.
• Most also have
• a pair of mandibles
• a pair of appendages on each body segment
• some branched appendages
• 16 to 20 segments
• several tagmata
• Many have a free-swimming
• larval stage called a nauplius.

http//copepodes.obs-banyuls.fr/images/NAUPLIUS.jp
g
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a. Terrestrial Crustaceans

• Sow bugs and pill bugs are terrestrial isopods.
• They lack adaptations for conserving water and
  live only in moist environments.
• They generally feed on decaying vegetation.
• Pill bugs roll into a ball when disturbed or
  threatened.

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b. Aquatic Crustaceans (many species)

• Copepods -important part of the oceans plankton.
  
• In freshwater, much of the plankton are water
  fleas such as Daphnia species.
• Barnacles are sessile as adults.
• Free-swimming barnacle larvae attach to surfaces
  and develop a shell that encloses the body.
• Barnacles use their cirri (singular, cirrus) to
  sweep food.

www.divediscover.whoi.edu
www.microscopyu.com
www.ryanphotographic.com
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More aquatic crustaceans

• Order Decapoda -means10 feet
• Decapods have five pairs of legs
• Crayfish, lobsters, crabs, and shrimp are
  decapods
• Respiration through gills
• (see more about crayfish in detail at end of
  chapter- know parts for dissection lab)

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4. Subphylum Chelicerata

• Defined by presence of chelicerae
• The first pair of appendages
• Modified into pincer or fangs
• Class Arachnid- spiders, scorpions, mites, ticks
• Some important Parts
• Chelicerae ( in spiders fangs to inject poison)
• Pedipalps (hold food)
• 8 simple eyes at anterior of cephalothorax (NOT
  compound eyes!)
• Spinnerets- 3 pairs on tip of abdomen, for making
  silk
• Book lungs- like folds in a book lots of surface
  area for gas exchange (some spiders use Tracheae
  for respiration instead)
• Malpighian Tubes- excretory tubes collect wastes,
  liquids. The liquid is reabsorbed (to conserve
  water) waste is nearly solid.

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Spiders-A full facial view of any spider shows
its killing ability.

• Two powerful chelicerae, protrude down
• Each chelicera bears a hinged fang.
• Both fangs have ducts that lead up to the venom
  glands within the head.
• Spiders fall into two groups, each being
  classified upon how they strike their prey.
• The fangs of Tarantulas are so hinged that they
  articulate in a front-to-back motion allowing
  them to strike their prey from above.
• Most other spiders have fangs that are hinged
  laterally, providing a left-to-right strike.

www.microscopix.co.uk/spiders/fangs/index.htm
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Spider Chelicerae
Fangs and Chelicerae of Tarantula
SpiderlingBrachypelma smithi(Mexican Red-Knee
Tarantula)
Fangs, Chelicerae of Zebra Jumping
SpiderSalticus scenicus
www.microscopix.co.uk/spiders/fangs/index.htm
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Anatomy of a spider

• Mites and ticks differ from spiders because
  they
• have a fused cephalothorax and abdomen.

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Life of a Spider

• Spiders feed on insects and other small animals.
  Many species are adapted to capture certain prey.
• Spiders rarely harm humans, but two species in
  the United States are dangerous
• the black widow
• the brown recluse
• A male spider is usually smaller than the female.
  
• Females lay eggs in a silken case.

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5. Subphylum Hexapoda

• Class Insecta
• By many standards- the most successful group of
  animals on earth.
• Entomology- the study of insects terrestrial
  arthropods.
• Body of an insect is divided into 3
  tagmata
• Head
• Thorax
• Abdomen

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bugs

• Because they dominate all terrestrial
  environments that support human life, insects are
  usually our most important competitors for food,
  fiber, and other natural resources.

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See page 743 for common insect orders

• See Example organism Grasshopper
• Please note parts for dissection lab, see p 745
  text.

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The crayfish- next 4 pages are notes for
dissection lab

• an abundant freshwater crustacean that is
  structurally similar to lobsters, which are
  marine crustaceans.
• Crayfish, lobsters, crabs, and shrimp are
  decapods, or members of the order Decapoda.
  Decapoda means 10 feet.
• Decapods have five pairs of legs that are used
  for locomotion.

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External Structure

• The crayfishs body is divided into
• the cephalothorax, which is covered by the
  carapace and is divided into
• the head, which has five segments
• the thorax, which has eight segments
• the abdomen, which is is divided into six
  segments
• A pair of appendages is attached to each segment
  of the crayfish. Several pairs have specialized
  functions.
• These appendages include
• Antennae
• Antennules
• Mandibles
• Maxillae
• Maxillipeds
• Chelipeds
• Walking legs
• Swimmerets

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Crayfish -Parts for lab
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• Excretion
• Green glands assist in excretion of excess water
  that enters the body by osmosis.
• Digestion
• Digestive gland near the stomach secretes enzymes
  for digestion.
• Respiration
• gills.
• Circulation
• open.
• Nervous Sensory Organs
• Many small sensory hairs. (sense water vibrations
  chemicals) Compound eyes are set on two stalks.

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Chapter 37 Insects

• Entomologists classify insects into more than 25
  orders based on characteristics such as
• structure of mouthparts
• number of wings
• type of development

• Factors responsible for their success include
• ability to fly -exoskeleton
• jointed appendages -small size
• large numbers offspring -short life span

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Just how dominant are insects?
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Comparison of 2 of the 5 groups of Arthropods
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Insects as Food

• http//www.cals.ncsu.edu/course/ent425/text01/inde
  x.html
• Insects were undoubtedly an important source of
  nutrition for our early human ancestors.  Even
  today, they are still collected and eaten by
  people of many cultures.  In Mexico, dried
  grasshoppers are sold in village markets.  High
  in protein and low in fat, they may be fried or
  ground into meal and mixed with flour to make
  tortillas.  Sago grubs, the larvae of a
  wood-boring beetle, are considered a delicacy in
  Papua New Guinea.  The islanders boil the larvae
  or roast them over an open fire.  Ants, bees,
  termites, caterpillars, water bugs, beetle
  larvae, flies, crickets, katydids, cicadas, and
  dragonfly nymphs are among a long list of edible
  insects that provide nutrition for the people of
  Australia, Africa, South America, the Middle
  East, and the Far East.  Indeed, Americans and
  other descendents of western European culture
  appear to be unique among peoples of the world in
  having such a strong cultural taboo against the
  use of insects as food.
• Silkworm pupae forhuman food inThailand

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A Recipe for Maggot Crispies

• 1/4 cup margarine4 cups small marshmallows3
  cups crispy cereal3 cups dry roasted maggots or
  mealwormsIn a saucepan, melt margarine and
  marshmallows. Remove from heat and stir in cereal
  and maggots. Spread mixture in a 9x13 greased pan
  and allow to cool.

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Insect body is divided into three tagmata

• Head -has mandibles and one pair of unbranched
  antennae.
• Thorax -has three pairs of jointed legs and, in
  many species, one or two pairs of wings.
• Abdomen -has 9 to 11 segments but neither wings
  nor legs in adults.

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Insects and People

• Insects negatively affect humans by
• competing for food
• transmitting diseases
• destroying buildings other manufactured
  products
• Insects benefit humans by
• serving as food for other animals
• pollinating flowers
• making valuable products such as honey
• recycling nutrients in ecosystems

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External Anatomy Grasshopper
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Internal Anatomy Grasshopper
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Grasshopper body- three tagmata

• The head
• mouthparts -labrum labium are mouthparts that
  function like upper and lower lips, respectively.
• a pair of unbranched antennae
• pairs of simple and compound eyes.
• The thorax is composed of
• Prothorax
• Mesothorax
• Metathorax
• The abdomen has upper and lower plates

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Insect mouthparts
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Circulation, Respiration, Excretion

• Insects have an open circulatory system that
  transports nutrients through the body.
• Gas exchange occurs by means of air-filled
  tracheae that reach deep into the body.
• Malpighian tubules remove cellular wastes from
  the hemolymph while conserving water.

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Nervous system

• The grasshoppers central nervous system consists
  of a brain and a ventral nerve cord with ganglia
  located in each body segment.
• Nerves extend from the brain to sensory
  structures.
• Insect sensory structures include
• simple and compound eyes
• sensory hairs on antennae and other body parts
• in some species, a sound-sensing tympanum

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Reproduction

• Grasshoppers have separate sexes,
• as do all insects.
• During mating, the male deposits sperm into the
  females seminal receptacle, where the eggs are
  fertilized internally.
• The last segment of the females abdomen forms
  the ovipositor, which she uses to lay fertilized
  eggs.

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Most insects go through metamorphosis.

• In incomplete metamorphosis, a nymph hatches from
  an egg and resembles the adult but has
  undeveloped reproductive organs and no wings. The
  nymph molts several times to become an adult.
• In complete metamorphosis, a wormlike larva
  called a caterpillar hatches from an egg and
  molts several times before becoming a pupa. The
  pupa molts to produce the adult, which resembles
  neither the larva nor the pupa.

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Incomplete vs. Complete metamorphosis
Complete metamorphosis -allows larvae and
adults of the same species to avoid competing
for space and food. -allows survival in
periods of harsh weather or scant resources.
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See writing assignment sheet