Phylum Arthropoda:

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Phylum Arthropoda

• Blueprint for Success
• Chapter 14 and 15

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Characteristics of Arthropods

• Modified segmentation body regions specialized
  for specific functions (tagmatization).
• Chitinous exoskeleton used for support and
  protection
• Paired, jointed appendages
• Growth accompanied by molting (ecdysis)

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Characteristics of Arthropods

• Ventral nervous system
• Reduced coelom
• Open circulatory system where blood is released
  into tissue spaces (hemocoel)
• Complete digestive tract
• Metamorphosis often present

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Arthropods

• Successful in almost all habitats on the earth.
• Most abundant animals Several million species
  identified
• 30 to 50 million species may yet be undescribed
• Triploblastic, protostome development
• Exhibit bilateral symmetry
• Four aspects contribute to arthropod success.
• 1. Metamerism
• 2. Exoskeleton
• 3. The Hemocoel
• 4. Metamorphosis

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Metamerism

• Segmentation, most evident externally
• Each external segment bears a pair of appendages
• Body cavity not divided internally
• Permits the specialization of regions of the body
  for specific functions
• Regional specialization Tagmatization
• Body regions (tagmata) specialized for feeding,
  sensory perception, locomotion, visceral
  functions.

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The Exoskeleton

• External, jointed skeleton which encloses
  arthropods
• Provides support, protection, and prevents water
  loss
• System of levers for muscle attachment and
  movement
• Secreted by epidermal cells
• Epidermis covered by exoskeleton on outside
• Consists of two layers
• 1. Epicuticle outermost, waxy lipoprotein layer
• 2. Procuticle/Endocuticle bulky inner layer
  made of chitin

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The Exoskeleton

• Hardening of the procuticle provides armor-like
  protection
• Modifications of the exoskeleton
• Formation of joints
• Sensory receptors (bristles, lenses, etc)
• Gas exchange
• Must be periodically shed for growth (ecdysis)

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The Exoskeleton

• Epicuticle and Procuticle

epicuticle
exocuticle
procuticle
endocuticle
epidermis
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The Hemocoel

• Provides an internal cavity for the open
  circulatory system of arthropods
• Allows for the exchange of nutrients, wastes, and
  (sometimes) gases

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Metamorphosis

• Indirect development, a significant change in
  physiology as the immature form becomes an adult
• Reduces competition between adults and immature
  stages

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Metamorphosis

• Evolution of arthropods has resulted in an
  increasing divergence of body forms, behaviors,
  and habitats between immature and adult stages.
• Ex Larval crabs feed on plankton, adult crabs
  prowl sandy bottoms for live prey.
• Ex Caterpillar feeds on leafy vegetables, adult
  butterfly feeds on nectar from flowers.

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Subphylum Crustacea

• Examples
• Crayfish, crabs, lobster, shrimp, barnacles and
  copepods.
• Two unique characteristics
• 1. Two pairs of antennae
• 2. Biramous appendages
• Five classes of crustaceans and numerous orders
• Class Malacostraca
• Class Maxillopoda
• Class Branchiopoda
• Class Remipedia
• Class Cephalocarida

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Class Malacostraca

• Soft Shell
• Largest class of crustaceans
• crabs, lobsters, crayfish, shrimp, krill, isopods
• Body divided into two regions
• 1. Cephalothorax (fusion of sensory/feeding and
  locomotion tagmata)
• 2. Abdomen (a muscular tail)

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Class Malacostraca

• Paired, biramous appendages in both body regions
• Appendages on Cephalothorax
• Pairs 1 and 2 Antennae (TWO pairs!)
• Pairs 3 through 5 Mouth appendages
• Mandible Pair (Chewing)
• Maxillae (Food handling)
• Pairs 6 through 8 Maxillipeds
• Accessory sensory and food handling appendages
• Pairs 9 through 13 Pereopods (Walking legs)
• Cheliped (Pincher-like)
• Appendages on Abdomen
• Pleopods (Swimmerets)
• Telson used

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Class Malacostraca
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Class Malacostraca

• Reproduction

• All crustaceans are dioecious
• Mating occurs after molting of the female
• In females, developing eggs attach to pleopods
  and are brooded until hatached
• In males, pleopods are modified into claspers and
  used for sperm transfer
• Crayfish have direct development

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Class Malacostraca

• Feeding

• Predators, herbivores, scavengers
• Foregut includes an enlarged stomach, specialized
  for grinding
• Midgut intestine
• Short hindgut ends in anus and used for water
  and salt regulation

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Class Malacostraca

• Gas Exchange Circulation

• Sensory Regulation

• Gills in gill chamber
• Between the carapace and body wall
• Muscular Heart
• Dorsal, anterior, and posterior arteries empty
  into sinuses of hemocoel

• Ventral nervous system
• Compound eyes
• Crayfish Excretion organs are called green
  glands
• Other crustaceans maxillary glands

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Class Maxillopoda

• Includes Barnacles and Copepods
• Copepods are most abundant crustacean
• Marine and Freshwater
• Barnacles are sessile
• Marine only
• Most monoecious
• Attach to various substrates
• Some are parasitic

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Subphylum Hexapoda

• 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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Class Insecta

• 30 Orders within Class Insecta!
• Adult Generalized Insect Characterized by
• Body divided into head, thorax, abdomen
• Three pairs of legs
• Two pairs of wings

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Class Insecta Body Plan

• Head
• Single pair of antennae
• Mouthparts
• Compound eyes
• 0 to 3 ocelli (simple eyes)
• Thorax
• Three segments prothorax, mesothorax, metathorax
• One pair of legs attaches to each thoracic
  segment
• Pair of wings attach at margin between mesothorax
  and metathorax
• Abdomen
• 10 to 11 abdominal segments

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Insect Flight

• Insects utilize many forms of locomotion walk,
  run, jump, swim, but flight is perhaps the most
  important
• Insects were the first animals to fly
• Important from an evolutionary perspective!
• 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.

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Insect Flight

• Synchronous (Direct) Flight
• Used by butterflies, dragonflies, and
  grasshoppers.
• Flight muscles act on wing bases
• A single nerve impulse in flight muscles results
  in a single wing cycle
• Asynchronous (Indirect) Flight
• Used by flies and wasps
• Flight muscles act on body wall
• Changes in shape of the thorax cause wing
  movements.
• A single nerve impulse results in many cycles of
  the wings

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Insect Feeding

• Variations in mouthparts include specializations
  for sucking or siphoning plant or animal fluids
• Mouthparts
• Labrum- upper liplike structure, sensory and not
  derived from paired appendages
• Mandibles- chewing mouthparts
• Maxillae- have cutting surfaces and a sensory
  palp
• Labium- sensory lower lip
• All aid in food handling

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Insect Digestive System

• Long and straight and consists of the foregut,
  midgut, and a hindgut.
• Foregut
• Behind pharynx is a crop that is used for storage
• Proventriuculus or gizzard moves food to midgut
  helps grind
• Midgut
• Aids in digestion and absorption
• Gastric cecae increase surface area
• Hindgut
• Primarily involved with reabsorption
• of water

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Insect Gas Exchange

• Gas exchange with air requires a large surface
  area for the diffusion of gases
• Accomplished through highly branched systems of
  chitin-lined tubes called tracheae
• Tracheae open to outside of body through
  spiracles
• Spiracles can close to prevent water loss
• Most insects have ventilating mechanisms
• Moves air into and out of tracheal system
• Contracting flight muscles
• Passive suction (vacuum) draws air in
• Abdominal muscle contraction (pump)

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Insect Circulation

• 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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Insect Sensory Functions

• Ganglion in head region
• Sense organs specialized for functioning on land
• Insects are capable of some learning have a
  memory
• Bees recognize flowerlike objects
• When bees are rewarded with nectar, they will
  choose flowers with that same odor in subsequent
  trials
• Capable of detecting light
• Used in orientation, navigation, feeding, etc
• Compound eyes are well developed in adults