3.2 Exploring Animal Diversity
Big ideas to keep in mind
• Animals are multicellular, heterotrophic, eukaryotic
organisms
• Each animal has a unique body plan that reflects its
evolutionary history
• Animals are often classified as invertebrates or
vertebrates
• Chordates are the group of animals most closely
related to humans
Biodiversity evolves over time and is affected by
changing conditions on Earth
Coral Reefs
• Biodiversity hot spots
• Home to more than 25%
of Earth’s marine species
A polyp builds coral
• Tiny creatures called polyps create the coral reef
• The polyps have a symbiotic relationship with
photosynthetic protists, such as dinoflagellates
• Therefore, reefs are only found in shallow, sunlit
water
Coral Reefs
• Human activities such as mining, agriculture,
pollution, and overfishing can threaten or destroy
shallow-water habitats
• Stressed polyps reject the symbiotic protists,
resulting in bleached, unhealthy reefs
• This occurs because protists cannot live in lower pH,
acidic waters
• How might water become acidic?
What Are Animals?
• More than a million living species of animals are
organized into about 35 major groups called phyla
• As diverse are animals are, the share 6 key
characteristics that separate them from other
organisms:
– Animals are eukaryotic
– Animals cells lack cell walls
– Animals are multicellular
– Animals are heterotrophs that ingest food
– Animals are motile at some point in their life cycle
– Animals form a blastula during embryonic development
Evolution of Animals
• Both plants and animals show evolutionary change
that reflects a movement of ancient species from
water onto the land
• We will not cover all the phyla, but will focus on
some that exhibit important evolutionary steps that
include changes to the body plan
• Body Plans: each species has a unique body
structure
– Includes structural details and features such as type of
symmetry, presence of a body cavity, embryological
development, segmentation, presence of a head,
presence of vertebrae, placement and number of limbs
and mobility
• Levels of Organization: remember, cells are the
functional unit of life
– Cells become specialized and organize into tissues
– Tissues are groups of cells that perform a particular
function
– Groups of tissues can form organs
– Organs can work together to form systems
– An organism can contain a variety of systems
• Body Symmetry: can give you insight into an
animals movement and evolution
– Asymmetrical: no symmetry
– Radial Symmetry: body parts arranged around a central
axis
– Bilateral Symmetry: mirror image right and left sides,
this is the most common form of symmetry in the animal
kingdom, results in:
Cephalization: development of a distinct head with
sense organs
• Embryological Development: all animals begin life
as a zygote that forms when a sperm fertilizes an
eggs
– The zygote splits into two cells, then four cells and so on
– Eventually a hollow ball of cells called a blastula forms
and an infolding of cells occurs at a particular spot in the
ball
– The infolding eventually pushes all the way through the
hollow ball forming a tube that connects both ends, this
becomes the digestive tract
– Depending on the animal, the first opening (blastopore)
becomes either the mouth or anus
– If it develops into a mouth = protostome
– If it develops into an anus = deuterostome
• Segmentation: repeating parts
– Many bilaterally symmetrical animals have repeating
parts called segments
– Worms have segments that are all very similar except for
a distinct head and tail
• Limbs: legs, flippers and wings
– Animals with bilateral symmetry and cephalization also
tend to have paired limbs = external appendages that
extend from their bodies
• Why is classifying all these features important?
These features help biologists sort animals into
phyla to build a phylogenetic tree! (page 68)
Major Groups of Animals
• One common way to group animals is based on
whether they have a backbone
• Animals with a backbone are called vertebrates and
those without one are called invertebrates
• You are probably more familiar with vertebrates,
what percentage of the animal kingdom is
comprised of invertebrates?
• Invertebrate Video
Vertebrates
• Vertebrates make up most the of chordates phylum
• Vertebrates includes fish, amphibians, reptiles,
birds, mammals and humans
• 2 unique features of vertebrates are that they have
a skull and backbone
– skeletal features that protect the central nervous system
Phylogenetic Tree of Vertebrates
• You can see the diversity of vertebrates in the
phylogenetic tree on page 73 (read page 72 first!)
• This is based on one set of hypotheses for the
evolutionary history of living vertebrates
• To construct this, anatomical, molecular and fossil
evidence was used
• The branching points represent important steps in
vertebrate evolution