Download The Arthropods:

 Most
successful land
animals in terms of
numbers of species
and individuals
 Bodies divided into
three tagmata
 Five pairs of head
appendages
 Three pairs of legs on
thorax
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30 Orders within Class Insecta!
Common features an adult Insect is characterized by:
o Body divided into head, thorax, abdomen
o Three pairs of legs
o Wings
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Head
o Single pair of antennae
o Mouthparts
o Compound eyes
o 0 to 3 ocelli (simple eyes)
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Thorax
o Three segments: prothorax, mesothorax, metathorax
o One pair of legs attaches to each thoracic segment
o Pair of wings attach at margin between mesothorax and metathorax
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Abdomen
o 10 to 11 abdominal segments
o Spiracles-openings to tracheal system
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Insects utilize many forms of locomotion:
walk, run, jump, swim, but flight is perhaps
the most important
Insects were the first animals to fly
o Important from an evolutionary perspective!
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Wings most likely evolved from outgrowths
of the thorax which protects the legs
Required thermoregulation
Some insects use a synchronous (direct)
flight mechanism which others use an
asynchronous (indirect) flight mechanism.

Synchronous (Direct) Flight
o Used by butterflies, dragonflies, and grasshoppers.
o Flight muscles act on wing bases
o A single nerve impulse in flight muscles results in a
single wing cycle
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Asynchronous (Indirect) Flight:
o Used by flies and wasps
o Flight muscles act on body wall
o Changes in shape of the thorax cause wing
movements.
o A single nerve impulse results in many cycles of the
wings
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Variations in mouthparts include
specializations for sucking or
siphoning plant or animal fluids
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Mouthparts:
o Labrum- upper liplike structure,
sensory and not derived from
paired appendages
o Mandibles- chewing mouthparts
o Maxillae- have cutting surfaces
and a sensory palp
o Labium- sensory lower lip
o All aid in food handling
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Long and straight and consists of the foregut, midgut, and a
hindgut.
Foregut
o Muscular pharynx with a crop behind it that is used for storage
o Proventriculus (gizzard) moves food to midgut/helps grind food
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Midgut
o Aids in digestion and absorption
o Gastric cecae increase surface area
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Hindgut
o Primarily involved with reabsorption
of water
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Gas exchange with air requires a large surface area for the
diffusion of gases
o Accomplished through highly branched systems of chitin-lined tubes
called tracheae

Tracheae open to outside of body through spiracles
o Spiracles can close to prevent water loss
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Most insects have ventilating mechanisms
o Moves air into and out of tracheal system
o Contracting flight muscles
o Passive suction (vacuum) draws air in
o Abdominal muscle contraction (pump)
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Open circulatory system similar to other arthropods but
blood vessels less well developed
Blood carries nutrients, hormones, wastes
Blood is not important in gas exchange
Most insects are ectotherms, but some generate heat using
flight muscles
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Ganglion in head region
Sense organs are specialized for functioning
on land
Insects are capable of some learning have a
memory
o Bees recognize flower-like objects
o When bees are rewarded with nectar, they will
choose flowers with that same odor in subsequent
trials

Capable of detecting light
o Used in orientation, navigation, feeding, etc
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Compound eyes are well developed in adults
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Primary excretory
structures-Malphigian
tubules and the rectum
Malphigian tubules
remove nitrogenous
wastes from hemocoel
The rectum excretes uric
acid, which reduces
water loss but uses most
of the energy the insect
gets from food.
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Sex pheromones-used to attract mates
Caste-regulating- controls development of
individuals in a colony.
Alarm-warns other individuals of danger,
may cause flight from or attack on the site
Trailing- Help other members of a colony
identify location and quantity of food
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http://www.nhptv.org/wild/hexapoda.asp
 Four
classes, two major:
o Diplopoda- 2 pairs of legs per segment, body
round in cross section. Millipedes
o Chilopoda-1 pair of legs per segment, body oval
in cross section, poison claws. Centipedes
Pink Dragon Millipede
Scolopendra gigantea
Vietnamese Centipede
House Centipede