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14.1 Simple Animals
Page 452-456
Sarah Mai
SBI 3U1-02
April 7th 2011
What is an animal?
• Animals vary from microscopic organism that live in water, to
largest land animals.
• Common characteristics for all animals are:
They are heterotrophic, multicellular eukaryotes. They
cannot make their own food so they must ingest other
organism.
Their cells lack cell walls and have only cell membranes
surrounding the cell contents.
They have two types of tissue that are only found in
animals: nervous tissue and muscle tissue.
Most animal reproduce sexually. The diploid stage of the
life is dominant.
Body Plan of an Animal
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Biologist examine the features of an animal’s body plan in order to organize the
smaller taxa such as phyla and classes.
These features include:
The type of body symmetry. Does the body
look asymmetrical or does it show bilateral or
radial symmetry?
The degree of cell organization within the
body. Do cells exist independently or form
functional groups. Such as tissues or organs?
The presence of a coelom, or internal body
cavity, and other structural and physiological
modifications.
Figure 14.2 -The earliest animals are
thought to be related to this
choanoflagellate, a colonial protist.
The Simplest Animals
(Phylum Porifera)
• Some living sponges resemble the ancestral colonial protist.
• Sponges belong to the phylum Porifera and also vary in terms
in shape, and size depending on their habitat.
• Sponges are defines as sessile organism that stay in one place.
• 5000 species are identified as sponges, all aquatic and mostly
marine.
Figure 14.3 – The shapes, colours,
and sizes of sponges vary depending
on their aquatic environment.
Smaller sponges (top) live in shallow
marine water with strong tidal
action. Larger sponges with
branching structure (bottom) live in
deep, quiet waters and may grow to
be over a metre in height.
The Simplest Animal (cont’d)
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Sponges have a simple, asymmetrical body plan made up of a loose collection of cells.
They have no mouth, no digestive cavity, no muscles, and no nervous systems.
Within the animal kingdom, only sponges, the simplest multi-cellular organism, have an asymmetrical
body plan and lack definite cell layers.
Sponges absorb water through numerous tiny pores that cover the body and expel water through larger
opening called Oscula.
As water travels through canals within in sponge, the sponge absorbs oxygen and releases waste through
gad exchange and filters out small organism.
Cells have three main types of cells with special functions:
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Epithelial Cells- This covers the inner and outer
surfaces of the body. Some epithelial cells
surround pores and control their size to regulate
the flow of water.
Collar Cells – This cell maintain flow of water
through the sponge by beating a flagellum that
extends into the inner canal.
Amoeboid Cells – This cells helps pass food. It
moves between epithelial cells and the collar
cell. They digest, and distribute nutrients,
produce reproductive cells.
Figure 14.4 – Because sponges lack true
organs, differentiated cells such as the
epithelial, collar, and amoeboid cells,
perform specialized function at the cell or
tissue level.
The Two- Layered Animals
(Phylum Cnidaria)
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The first major changes from the poriferans are: they have symmetrical bodies with cells organized into
tissues.
Cnidarians include hydrozoans, jellyfish, sea anemones, and sea fans.
About 10 000 cnidarians species exits today.
They can be as small as a microscopic organism and also grow up to 2.5m wide.
All cnidarians show “radial symmetry”
Some ectodermal cells have muscle fibres that contract to move the animal.
Other ectodermal cells have a nerve net which allows the cnidarians to respond to environmental stimuli
Radial Symmetry- an organism that has body parts that repeat around one main axis point.
All cnidarians have stinging structure called “nematocyst”. These are located in specialized ectodermal cell
called cnidocytes.
Cnidocytes release toxic substance through the nematocysts to paralyze prey.
Figure 14.6 – the tentacles of jellyfish extend down from
the outer edge of a cuplike body. The tentacles of some
larger can grow to be 25 m long.
The Life Cycle of Cnidarians
Gastrovascular cavity has the function to digest, circulate, and exchange gas.
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The first stage- Polyp:
Looks like a cylinder and sits on an underwater surface with its tentacles extended.
They are asexual, and reproduce by budding.
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The second stage- Medusa:
 Floats like a bell or an umbrella, usually with its mouth and tentacles facing downward.
Figure 14.7- Cnidarians develop
into two different stages with
different body structure: the
flowerlike polyp and the bellshaped medusa.
The Life Cycle of Cnidarians (Cont’d)
• Medusae produce eggs and sperm which got released in water.
• Medusae produce eggs and sperm which will be released into the water.
• Once the eggs is fertilized, the eggs develop into a free-swimming larva
called a “planula”
• Once the planula reached the bottom, a new polyp is formed.
Figure 14.8- In many
cnidarians, the polyp and
medusa stage both enter the
life cycle. In jellyfish, a
fertilized egg develops into a
planula that develops into a
polyp. The polyp buds into
other polyps and the polyps
bud into the medusae. The
mature medusae produce and
fertilize new eggs.
The Life Cycle of Cnidarians (Cont’d)
Figure 14.9- The Portuguese man-of-war- us a
free-floating hydrozoans whose medusae and
polyps combine to form colonies.
Figure 14.10- Sea anemones have no protective
covering. Most coral polyps generate a protective
skeleton of calcium carbonate that produces
distinctive pattern in different coral species.
THE END!