Introduction to Animals

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Introduction to Animals
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To be an animal means

• Multicellular
• humans have 50 - 100 trillion cells
• Ingestive heterotroph
• Lacking a cell wall
• Specialization of cells
• (except Porifera)
• May involve movement sexual reproduction
  (formation of a zygote)

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Phylogenetic tree of animal kingdom

• Based on
• Body symmetry
• Patterns of embryo development
• Comparing fossils
• rRNA

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Symmetry

• Overall pattern of structure
• Asymmetric - No symmetry as with the Porifera
• Radial symmetry even cut along a diameter.
  Echinodermata and Cnidaria
• Bilateral symmetry even cut along a central
  plane. Worms, Arthropods, Mollusks, Echinoderms,
  and Vertebrates

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Trends in Animal Evolution

• As you go up the phylogenetic tree, you will see
  a greater tendency towards bilateral symmetry.
• Also a concentration of nerves (sensory organs)
  towards the front of the organisms known as
  cephalization

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Body views

1. Dorsal top/back
2. Ventral belly/bottom
3. Anterior front/head
4. Posterior tail/rear

Anterior (front)
Dorsal (top)
Ventral (bottom)
Posterior (tail end)
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Cleavage

• A series of cell divisions that occurs
  immediately following fertilization
• Mitosis occurs but cells do not grow in size.

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Stages in Cleavage
Gastrula Indented ball stage
Blastula Hollow ball stage
Morula Solid ball stage
Zygote
                                                
                                                  
              
During gastrulation, an indentation occurs.
A multi-layer embryo is formed with 3 germ layers
Blastopore opening of indentation
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• Protostome
• Blastopore developes into the oral opening
  (mouth)
• Mollusks, arthropods and annelids
• Deuterostomes
• Blastopore developes into anus
• Echinoderms and Chordates (thats us)

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Germ Layers

• Fundamental tissue types found in embryos of
  animals (but not sponges)
• Gives rise to every body feature, organs
  tissues
• 2 germ layers in Cnidaria 3 in all others
• Endoderm forms throat, gills, lungs and
  digestive tract (with pancreas and liver)
• Ectoderm forms outer skin, hair, nails and
  nervous system
• Mesoderm skeleton, muscles, inner skin layer,
  circulatory system and lining of the body cavity

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Body Cavities

• Acoelomates Body cavity is absent. As in
  Flatworms . Endoderm is connected solidly to
  mesodermal tissue
• Pseudocoelomates Body cavity contains three
  distinct layers but endoderm is not connected to
  mesoderm. Free floating in fluid. Found in
  roundworms.
• Coelomates True body cavity. Mesoderm lines
  body cavity while supporting endodermic.
  Mollusks, annelids, arthropods, chordates and
  echinoderms

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Systems through the Phyla

• Circulatory systems
• Closed Circulatory System
• One in which blood is always contained within a
  vessel. Heart serves as a pump. Found in
  annelids, chordates
• Open Circulatory System
• Pumps blood into spaces around the body tissues.
  From there the blood makes its way back to
  vessels that will carry it back to the heart, or
  possibly to holes in the heart itself. Found in
  Arthropods and some mollusks

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Skeletons

• Exoskeleton Rigid, outer covering protecting
  soft internal tissue. Found in Arthropods and
  mollusks. Needs to be shed (molt) as animal
  grows.
• Endoskeleton Internal skeleton. Best for
  larger organism. Found in echinoderms and
  vertebrates. Grows as animal grows.

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Reproduction

• Asexually by budding (Porifera, Cnidarians) or
  regeneration (Porifera, Planaria, Sea stars)
• Sexually
• Hermaphroditic contains both sexes (but not
  self fertilization necessarily). Think of your
  earthworm
• Separate sexes as you go up the phylogenetic
  tree

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Development

• Incomplete metamorphosis Direct development
  young animal is born or hatched looking like
  adult but smaller. No larval stage. Mantids,
  Grasshoppers, us
• Complete metamorphosis Indirect development
  intermediate larval stages appearing different
  from adult.
• Butterfly, flies, moths