Invertebrates

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Invertebrates

• Chapter 33

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Invertebrate Characteristics

• Lack a backbone
• 95 of known animal species
• Occupy almost every habitat on Earth

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Porifera

• No True tissues
• No symmetry
• Suspension feeders
• Most are hermaphroditic

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Cnidaria

• Radial symmetry
• All have cnidocytes
• Diploblastic
• Gastrovascular cavity (no anus)
• Carnivorous
• Body plan
• Polyp
• Medusa
• Simple muscle system
• Simple nerve net nervous system, no brain

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Cnidarian Classes

• Hydrozoa
• Alternate polyp and medusa in life cycle, with
  polyp as dominant stage
• Examples colonial hydroids, hydra, Portuguese
  Man of War
• Scyphozoa
• Prominent medusa
• Examples jellyfish
• Anthozoa
• Polyps are dominant
• Sea anemonies, and coral

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Acoelomates

• Lack coelom
• Bilateral symmetry
• What evolutionary novelty comes with bilateral
  symmetry?
• Cephalization

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Platyhelminthes

• What new novelties are seen in this phylum?
• Triploblastic, so has muscular system
• Organs
• Cephalization, more complex nervous system

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Three classes

• Turbellaria
• Carnivorous
• Moves by cilia
• Eyespots on head
• Rudimentary brain
• Diffusion for gas exchange
• Excretion through flame cells
• Hermaphroditic

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Trematodes

• Often called flukes
• All members are parasitic
• What makes a parasite in good standing?
• Become an egg machine since it is hard to find a
  host
• Use intermediate hosts
• Develop hooks and suckers
• Hermaphroditism, so that limits need to find
  others

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Cestode

• Tapeworms
• Parasitic
• Scolex in adult hooks onto the host intestines
• Proglottids for reproduction
• Eggs eaten by intermediate host and larva
  develops
• Final host infected by eating intermediate host
  encysted with larva forms
• Do not eat poorly cooked meats!

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Pseudocoelomates

• Not quite a true coelom, missing the inner lining
  of muscle

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Rotifera

• Mostly marine
• 1st to get an anus
• Organs lie in the pseudocoelom
• Parthogenesis unfertilized eggs develop into
  females

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Nematoda

• Many found in soil, useful for nutrient recycling
  
• Complete digestive tract
• Some are parasitic, e.g. trichinella and hookworm
  (dogs)

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CoelomatesProtostomes

• Mouth develops from the blastopore
• Cleavage is radial and determinate
• ALL HAVE A TRUE COELOM!

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Mollusca

• Bilateral symmetry
• Open circulatory system
• Soft bodied, with hard shell protection
• Most have exoskeletons
• Reduced or no segmentation
• Radula rasping tongue to scrape food
• True coelom
• Many internal organs
• Three body parts
• Foot
• Visceral mass
• Mantle

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Four Classes

• Polyplacophora
• Chitons
• Cling to rocks
• Live on rocky shores
• Use muscular foot to grip
• Gastropods
• Snails, slugs, nudibranchs
• Largest class
• Shell protects body
• Torsion leads to twisted body
• Uses radula to scrape algae and graze on plants

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Four classes

• Bivalves
• Clams, oysters, mussels, scallops
• Possess shell divided and hinged into two halves
• Filter feeders
• Sedentary lifestyle
• Cephalopods
• Squid and octopus and nautilus
• Use jaws to bite prey
• Mouth as base of foot (foot drawn into several
  tentacles)
• Complex brains and capable of learning and moving
  fast
• Mantle reduced or absent
• Can get large, How?

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Annelids

• SEGMENTATION!
• Closed circulatory system
• Alimentary canal
• Five pairs of hearts
• Gas exchange across skin
• Metanephridia for gas exchange
• Nitrogenous wastes exit from each segment through
  pores
• Nervous system with ganglia and ventral nerve
  cords

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Three classes

• Oligocheates
• Earthworms
• Polycheates
• Fanworms
• Tube dwellers (marine)
• Hirudinea
• Leeches
• Used to treat bruised tissues and to stimulate
  circulation

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Evolutionary trends in Annelids

• Coelom
• Serves as hydrostatic skeleton
• Developed complex organ system
• Protects internal structures
• Segmentation
• Specialization of body segments

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Arthropods

• Key characteristics
• Jointed appendages
• Segmentation
• Hard exoskeletons
• Extensive cephalization
• Open circulatory system
• Gas exchange gills in water, book lungs or
  spiracles on land

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Success vs. Limitations

• Successes
• Exoskeleton, lets them thrive on land, but
  limited
• Jointed appendages allowed for walking and then
  flying in some
• More successful organization of segments
• Limits
• Exoskeleton is shed
• Limited brain size
• Limited body size

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Subphyla

• Trilobites
• Extinct group
• Show pronounced segmentation, with little
  variation in appendages
• Early, primitive arthropods
• Chelicerates
• Includes the arachnids
• 1-2 body segments with 8 legs
• Uniramia
• Includes insects, millipedes and centipedes

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Classes

• Arachnids
• Scorpions, spiders, mites
• Insects
• 1 pair of antennae
• 6 legs
• 3 body segments
• Crustaceans
• Crabs, crayfish, lobsters, isopods (pill bugs)
• 2 or 3 body segments

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Deuterostomes

• Radial indeterminate cleavage
• Blastopore becomes the anus

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Echinoderms

• Secondarily evolved radial symmetry
• Unique water vascular system
• Has mouth and anus
• Has endoskeleton

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Classes

• Aseroidea
• Sea stars
• Ophiuroidea
• Brittle stars
• Echinoidea
• Sea urchins and sand dollars
• Holothuroidea
• Sea cucumbers

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To what phylum does this organism belong?

• Phylum Annelida

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To what phylum does this organism belong?

• Phylum Cnidaria

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To what phylum does this organism belong?

• Phylum Mollusca

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To what phylum does this organism belong?

• Phylum Echinodermata

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To what phylum does this organism belong?

• Phylum Arthropoda

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To what phylum does this organism belong?

• Phylum Nematoda

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To what phylum does this organism belong?

• Phylum Platyhelminthes

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To what phylum does this organism belong?

• Phylum Porifera

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What evolutionary innovation both led to and
limited the success of the phylum to which this
organism belongs?

• . . . the exoskeleton

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What type of symmetry does this organism exhibit?

• . . . none

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What evolutionary innovation does the phylum to
which this organism belongs have over Nematoda?

• . . . segmentation

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What is unique about the digestive system of this
organism, and others that belong to the same
phylum?

• . . . it is one way having both a mouth and an
  anus

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What two evolutionary innovations are common to
the phylum to which this organism belongs?

• . . . bilateral symmetry and cephalization

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What type of symmetry does this organism, and
others belonging to the same phylum, exhibit?

• . . . radial symmetry

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What evolutionary innovation is first exhibited
by the phylum to which this organism (a giant
squid) belongs?

• . . . the coelom

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An open circulatory system limits the size of
these animals
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The closed circulatory system is much more
efficient!
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