3.2 Exploring Animal DiversityBig 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

• 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

A polyp builds coral

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