Introduction to Kingdom Animalia

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Introduction to Kingdom Animalia
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Defining Animals 1. Animals are multicellular,
heterotrophic eukaryotes. 2. Animals generally
store their carbohydrate reserves as glycogen
3. Animal cells possess a number of unique
cellular structures, e.g., gap junctions -
intracellular junctions that allow the passage of
materials between cells 4. Animals possess
special tissues that are responsible for impulse
conduction (nervous tissue) and movement (muscle
tissue). 5. Most animals reproduce sexually,
with the diploid stage dominating the life cycle
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• Animal Phylogeny
• Origin of most animal phyla and major body plans
  took place in Precambrian era and early Cambrian
  period of the Paleozoic era (circa 500-600 mya)
• Most systematists agree that the animal kingdom
  is monophyletic
• By the early Cambrian period (about 550 mya),
  virtually all known animal phyla had evolved from
  the first animals of the late Precambrian

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• Trends in Animal Evolution
• 1. The first trend was a shift from a body plan
  called radial symmetry to a body plan referred to
  as bilateral symmetry
• Radial symmetry - a circular body plan having a
  central axis from which structures radiate
  outward
• Bilateral symmetry - a body plan in which the
  right and left sides of the body are mirror
  images of each other central longitudinal plane
  divides the body into 2 equal but opposite halves

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• Trends in Animal Evolution cont.
• 2. A trend toward increasing cephalization - the
  development of a distinct head, which has
  associated with it a brain and various kinds of
  sensory structures
• 3. A change from a simple sac-like body with a
  single opening at one end to a more complex,
  elongated body containing a tube called the "gut"
  with openings at both ends
• 4. A change from a tube enclosed in solid tissue
  toward suspension of the tube in a fluid filled
  space
• 5. An increase in body segmentation - the
  development of a series of body units, each
  containing similar sets of muscles, blood
  vessels, nerves. etc.

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Major Events in Animal Phylogeny
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Major Events in Animal Phylogeny cont.
1. The Parazoa-Eumetazoa Split Two basic kinds
of animals evolved early in animal evolution. A.
Parazoa ("beside the animal") - animals that lack
true tissues. e.g., Sponges B. Eumetazoa -
animals with well defined tissue layers, e.g.,
essentially all other animals.
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• Major Events in Animal Phylogeny cont.
• 2. The Radiata-Bilateria Split
• The eumetazoa are divided into 2 major branches
  depending on the type of body symmetry
• Some organisms exhibit radial symmetry, and are
  called the Radiata
• Other eumetazoa exhibit bilateral symmetry, and
  are called the Bilateria

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• 2. Radiata-Bilateria Split cont.
• The Radiata-Bilateria split is also defined by
  the differences in the number of germ layers that
  are formed in the embryo during gastrulation
• The Radiata are referred to as diploblastic -
  two germ layers form
• Ectoderm - covering the surface of the embryo
  gives rise to the epidermis and in some phyla the
  nervous system.
• Endoderm - inner most germ layer lines the
  primitive gut gives rise to the lining of the
  digestive tract and associated organs, such as
  the liver and lungs of vertebrates
• The Bilateria are triploblastic in addition to
  the ectoderm and endoderm they produce a third
  germ layer, the mesoderm
• Mesoderm - germ layer between the ectoderm and
  the endoderm gives rise to muscles and to most
  other organs

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• Major Events (Branch Points) in Animal Phylogeny
  cont
• 3. The Acoelomate-Coelomate Split
• A. Acoelomates - animals with solid bodies there
  is no body cavity between the gut (endoderm) and
  the outer body wall.
• The other 2 body plans are often referred to as
  a tube within a tube body plan a fluid filled
  sac separate the gut from the outer body wall.
• A second important difference between
  acoelomates and animals having a body cavity is
  that animals with a body cavity have some sort of
  blood vascular system

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• 3. Acoelomate-Coelomate Split cont.
• B. Pseudocoelomates - animals in which the body
  cavity is not completely lined with mesodermal
  tissue
• The body cavity is called a pseudocoelom
• C. Coelomates - animals that have a fluid filled
  body cavity that is completely lined with tissue
  that is derived from the mesoderm.
• This kind of body cavity is called the coelom

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Animal Phylogeny cont. 4. The Protostome-Deutersto
me Split Coelomates, can be divided into 2
distinct groups protostomes and
deuterostomes. They are distinguished based upon
fundamental differences in early development,
including cleavage, fate of the blastopore, and
coelom formation
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4. The Protostome-Deuterstome Split cont A.
Cleavage Protostomes - Spiral, determinate
cleavage Deuterostomes - Radial, indeterminate
cleavage
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• 4. The Protostome-Deuterstome Split cont.
• B. Fate of the Blastopore
• During gastrulation, the rudimentary gut or
  archenteron forms it has a single opening called
  the blastopore
• A second opening forms later at the opposite end
  of the archenteron to produce a digestive tube
  with a mouth and anus
• Protostomes - the blastopore becomes the mouth
• Deuterstomes - the blastopore becomes the anus

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• 4. The Protostome-Deuterstome Split cont.
• C. Coelom Formation
• Protostomes - coelom formation is called
  schizocoelous development coelom forms by
  splitting of mesoderm
• Deuterostomes - coelom formation is called
  enterocoelous development coelom forms as
  outpockets from the endoderm