Symmetry:
A Visual Presentation
Bilateral Symmetry

Bilateral symmetry occurs when one
half of an object is the mirror image of
the other half.

Symmetry exists all around us and many
people see it as being a thing of
beauty.
Is a butterfly symmetrical?
At the beach there are
a variety of shells with
symmetry.
Under the sea there are also
many symmetrical objects
such as these crabs
and this starfish.
Animals that have bilateral
symmetry
THESE MASKS HAVE
bilateral SYMMETRY
These masks have a
line of symmetry from
the forehead to the
chin.
The human face also
has a line of symmetry
in the same place.
Human Bilateral Symmetry
The 'Proportions of
Man' is a famous work
of art by Leonardo da
Vinci that shows the
symmetry of the
human form.
Classification 4.1: Classify
animals according to type of
skeletal structure, method of
fertilization & reproduction, body
symmetry, body coverings, &
locomotion.
Phylum Porifera: asymmetrical
Invertebrate, no body tissues or organs
 Filter feeders
 Reproduce sexually w/fertilization &
asexually by budding
 Do not move as adults—only when
budding

Phylum Porifera: the sponges

This is what a sponge looks like; notice the
range of colors.
Phylum Porifera

A sponge reproducing
asexually through
budding.

A sponge doesn’t look
this.
Phylum Cnidaria: corals &
anemones






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Invertebrates
Have stinging cells (pneumatocysts) for hunting &
protection
Ingest food into a central body cavity
Radial symmetry
Many adults can move to escape danger or get
food
External sexual reproduction
Asexual reproduction through budding
Phylum Cnidaria: corals and
anemones

Notice the crab inside
Clownfish here
Phylum Cnidaria: corals and
anemones

Brain coral
Notice the
radial symmetry

Worms are in 3 different phyla

1. Flatworms =
Phylum Platyhelminthes

2. Roundworms =
Phylum Nematoda

3. Segemented worms =
Phylum Annelida
Worms

Invertebrates

Long bodies with no legs

Bilateral symmetry

Possess tissues, organs, and organ systems

Reproduce sexually and asexually
Flatworms: Phylum Platyhelminthes
Roundworms: Phylum Nematoda
Segmented Worms: Phylum
Annelida
Phylum Mollusca: the mollusks

Invertebrates

Soft, unsegmented bodies often covered by
a shell

Bilateral symmetry

3 major groups: gastropods, bivalves,
cephalopods
Phylum Mollusca: the mollusks,
gastropods

Example: snails

Have single external shell or no shell at all

Move by use of a muscular foot
Phylum Mollusca: the mollusks,
gastropods
Phylum Mollusca: the mollusks,
bivalves

2-shelled mollusks that filter feed

Examples: oysters, clams, scallops

Adult bivalves stay in one place or move
slowly through the water
Phylum Mollusca: the mollusks,
bivalves

Scallop
Oysters
Phylum Mollusca: the mollusks,
cephalopods

Examples: octopus, squid, cuttlefish, nautilus

Ocean-dwelling w/a “foot” adapted to form
tentacles around its mouth

Not all have shells

Capture prey by using tentacles

Swim with jet propulsion
Phylum Mollusca: the mollusks,
cephalopods

Squid, nautilus, cuttlefish, and octopus
Birds are in the Phylum Chordata

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Endothermic (produce & maintain body heat)
Vertebrate w/4 chamber hear
Bodies covered w/feathers
MOST can fly using their wings
– Puffins, penguins, kiwi, rheas, emus, & ostriches don’t
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Internal, sexual reproduction & lay eggs
Bilateral symmetry
Parents care for babies until they can fly
Bird examples

Kiwi
Emu
Puffin (can
fly but
doesn’t
usually)
Mammals are in the Phylum
Chordata
Endothermic
 Vertebrate w/4 chamber heart
 Skin covered w/fur or hair
 Most born live & nursed with mother’s milk
 Most walk or run on 4 limbs
 Bilateral symmetry
 Reproduce with internal, sexual
reproduction

Mammals are in the Phylum
Chordata
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Classified into 3 groups based on how
their young develop
1. Monotremes
2. Marsupials
3. Placentals
–
Mammals care for young for an extended
time.
Mammals: monotremes

most primitive mammals
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There are three species of monotremes, the duck-billed
platypus (Ornithorhynchus) and two spiny anteaters, or
echidnas (Tachyglossus and Zaglossus).
These mammals lay eggs; after the babies hatch, the
mothers nourish their young with milk.
Today, monotremes live only in Australia and New Guinea.
The name monotreme means "one-holed," referring to the
cloaca, a single hole that serves the urinary tract, anus, and
reproductive tract in monotremes.
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Monotremes
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Duck-billed platypus
Echidna
Marsupial Mammals

Marsupials (Megatheria) are pouched mammals whose
babies are born in a very undeveloped state; the young then
attach themselves to their mother's nipple.
– Many marsupials have a pouch that encloses the young.
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The biggest marsupial is the human-sized red kangaroo
(Macropus rufus); the smallest marsupial, the pilbara
(Ningaui timealeyi), would fit in a person's hand.
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Some commonly-known marsupials include the kangaroo,
opossum, Tasmanian devil, and koala. The only marsupial
in North America is the Virginia opossum.

Marsupials evolved during the late Cretaceous period,
about 100 to 75 million years ago, during the time of the
dinosaurs.
Marsupial Mammals
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Virginia opossum
Koala
Marsupial Mammals

3-week old red kangaroo
Marsupial Mammals

The pilbara mouse, world’s smallest
marsupial

Tasmanian devil
Phylum Arthropoda: the arthropods
Exoskeleton
 Segemented body
 Jointed appendages
 Bilateral symmetry
 Most reproduce sexually
 Specialized mouth parts for chewing food
 Move through use of legs
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Phylum Arthropoda

Includes crustaceans, arachnids, centipedes,
millipedes, and insects

Insects have wings for flying

Crustaceans include crabs and shrimp

Arachnids = spiders & ticks

Insects = mosquitoes, bees, grasshoppers, crickets
Phylum Arthropoda: Crustaceans

Woodlouse
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Shrimp
Crab
Phylum Arthropoda: Arachnids
Phylum Arthropoda: Centipedes and
Millipedes
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Centipedes with distinct poison fangs
Millipedes
Phylum Arthropoda: insects
Objective 6.1: Describe protective
adaptations of organisms, including
mimicry, camoflage, and chemical
defense.
Terms defined

Mimicry: defense strategy; an adaptation of an
organism that allows it to look like a more
dangerous one—see p. 727 in text

Camouflage: defense strategy/protection; an
adaptation that provides organisms with the ability
to blend in with their environments

Chemical defense: defense strategy/protection that
allows organisms to poison predators if eaten or
threatened; often are bright colored warning
predators of poisnous nature
How many butterflies do you see?