Unformatted text preview: AP BIOLOGY UNIT 11 (CH. 32) Kingdom: Animalia
Ch. 32. Introduction Animal Evolution
Multicellular, eukaryotic ingestive chemoheterotroph.
Animals have a dominant diploid life cycle and the only haploid cells are the gametes. Some exceptions occur (male
bees are unfertilized eggs and are therefore haploid!)
Most of the estimated 9 – 10 million species inhabit the seas.
Have a method of internal communication through chemicals or nerves.
Storage carbohydrate as glycogen.
Cell junctions (desmosomes, tight junctions and gap junctions) hold cells and tissues together and provide structure and
Have an extracellular matrix (ECM) composed of collagen, proteoglycans, adhesive glycoproteins, and integrins. This
is common to all animals but not other multicellular organisms.
The animal body is developed through:
Cleavage divides the zygote into smaller cells after fertilization creating a multicellular structure called a blastula
(hollow ball of cells filled with fluid)
Gastrulation rearranges the cells of the blastula to form a three layered structure.
Most animals have true tissues that allow for the development of complex structures. The only animals without true
tissues are the sponges (phylum Porifera). These are found in the Sub-Kingdom: Parazoa (“beside the animals”). All
other animals are in the Sub-Kingdom: Eumetazoa (“true animals”).
Most are motile at some time in life cycle. Larva (free-living, sexually immature form) may be only time in some
Animals can be classified according to body structure or pattern of development. BODY SYMMETRY
Lack true tissues and organs.
Have only 2 layers of cells
Thought to have evolved from a choanoflagellate (flagellated colonial protist)
E.g. Everything else!
Possess true tissues.
Eumetazoans divided into two branches based on their symmetry.
Radial Symmetry. Branch Radiata.
Phylum Cnidaria and Ctenophora.
Has a top (oral) and bottom (aboral).
Body parts arranged around a central body axis like
spokes on a wheel.
Adapted for a sessile (not motile) lifestyle.
Develop only two germ layers (tissue layers), the
ectoderm which becomes the outer covering and
nervous system of an organism and the endoderm
which forms the digestive tube lining. Two-layered
organisms are called diploblastic.
Bilateral Symmetry. Branch Bilateria.
Phylum Platyhelminthes (flatworms) through Chordata
Have a top (dorsal), bottom or belly (ventral), head
(anterior) and tail (posterior).
Develop three germ layers and are called triploblastic:
• Ectoderm. Forms epidermis of skin, nervous system
• Endoderm. Lining of digestive tract; liver, pancreas.
• Mesoderm. Form the skeletal, muscle, circulatory, lymphatic, reproductive, and excretory systems.
Knight/Animal diversity and phylogeny (ch 32) AP BIOLOGY UNIT 11 (CH. 32) DEVELOPMENT OF BODY CAVITY Animals can further be grouped according to the development of a body cavity called the coelom. A coelom is a fluid filled
cavity that is completely lined with mesoderm tissue. This cavity separates the digestive tract from the outer body wall. This
allows the digestive tube and other organs to move independently of body movements, it is used as a hydrostatic skeleton the
can be used as leverage during muscle contractions, and it cushions and protects the organs.
Triploblastic animals are grouped on the basis of the development of this cavity.
• Phylum: Platyhelminthes (flatworms)
• Has no body cavity between the digestive tract and outer wall.
• Have a single opening to the outside that functions as a mouth and anus. Posses only a
• Do not have a blood vascular system.
The rest of the animals have a tube-within-a-tube form. They have a mouth and an anus so food
moves in one direction only.
• Phylum: Rotifera, Nematoda.
• Has a fluid filled cavity that is incompletely or partially lined with
• Cavity develops between the mesoderm and endoderm.
• Phylum: Everything else! (Bryozoa, Phoronida, Brachiopoda, Mollusca,
Annelida, Arthropoda, Echinodermata, Chordata)
• Have a fluid filled cavity that is completely lined with mesoderm
• Cavity develops within the mesoderm so the cavity is completely lined.
• The digestive tract is suspended in the cavity and held in place with connective tissues called mesentery. PATTERN OF DEVELOPMENT OF EMBRYO The coelomates are further divided according the pattern of development that their zygote goes
through. As the zygote undergoes cleavage to form a morula (solid mass of cells) to a blastula (hollow
ball of cells), the cleavage and arrangement of these cells differs among groups of animals.
As the blastula folds inward creating the 3 layered gastrula (during a process called
gastrulation) the coelom, mouth and anus are formed. Within the coelomates there are two
ways in which these may form.
When the primitive gut is formed (archenteron) the first opening (called the blastopore) that
is formed will become either a mouth or an anus. The tube will continue to form until it has
made an opening at the other end, thus forming a continuous pathway for food to flow. (In
one hole and out the other!)
One other way that the coelomates are distinguished is by the way that the coelom forms. As
the archenteron and gut are being formed, the mesoderm can form as a split from the
mesoderm cells of the archenteron that widens to form the cavity. This is called
schizocoelous (“schizo-“ split) development. This contrasts to enterocoelous development in
which the coelom is formed as “outpocketings” of the archenteron. The mesoderm has
portions of it that buds off from the wall of the archenteron and hollows to for the coelom. Knight/Animal diversity and phylogeny (ch 32) AP BIOLOGY UNIT 11 (CH. 32)
Phylum: Bryozoa, Phoronida, Brachiopoda, Mollusca, Annelida,
• During the first early cell divisions, the cell divisions are
diagonal to the vertical axis of the embryo. Spiral
• The cells end up lying between other cells after they have
formed versus being on top of the other cells.
• The cells also undergo determinate cleavage. [look at
your development notes (Ch. 21) on this subject!]
• In protostomes (“mouth first”) this first opening will
become a mouth. The second opening will become the
• Coelom formed through schizocoelous processes. Deuterostome coelomates:
Phylum: Echinodermata, Chordata
• During the first early cell divisions, the cells divide at
right angles or parallel to the vertical axis of the
embryo. Radial Cleavage.
• The cells are above or below one another.
• These cells also undergo indeterminate cleavage.
• In deuterostomes (“mouth second”) this first opening
will become an anus. The second opening will
become the mouth.
• Coelom formed through enterocoelous processes. Knight/Animal diversity and phylogeny (ch 32) ...
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