The Animal Kingdom

What is an animal?•Multicellular •Eukaryotic•Heterotrophic•No cell walls•95% of all animals are “invertebrates.”

Trends in Animal Evolution•Our survey of the animal kingdom will start with simple animals and move to more complex ones.

•We will investigate “invertebrates” first and “vertebrates” later.

•Invertebrates- animals without a backbone

•Vertebrates- animals with a backbone

History of Invertebrates: Cambrian Period• Illustrates a radically

different picture of strange looking invertebrate life

• Major difference was the unique “body plans”

• Similarities with today’s invertebrates include:1) specialized cells, tissues, organs present2) body symmetry 3) segmentation4) some type of skeleton5) front/back6) many types of appendages and shells

Animal Phyla•There are nine major phyla of animals…1. Poriferans (sponges)2. Cnidarians (jellyfish)3. Flatworms (tapeworm)4. Roundworms (heartworm)5. Annelids (earthworm)6. Mollusks (clam)7. Arthropod (grasshopper)8. Echinoderm (starfish)9. Chordate (human)

Invertebrates

More complex

Animal Evolutionary Relationships

EVOLUTIONARY

TRENDS

Trends in Animal Evolution• Complex animals tend to have…1) Specialized cells Tissues Organs

Organ Systems2) Bilateral Symmetry (no symmetry

radial bilateral)3) Cephalization (head with sensory

organs)4) Body cavity called coelom

(acoelomate pseudocoelomate coelomate)

5) Complex embryonic development

Trend #1: Cell Specialization and Internal Body Organization.•The more complex the animal, the

more “specialized” its cells become.•Cells Tissues Organs Organ

system.•Some animals have no organs-

sponges•Some animals have simple organs for

excretion and reproduction – flatworms

•Some animals have organ systems - mollusks

Trend #2: Body Symmetry

•With the exception to sponges, every animal exhibits one of two types of body symmetry:1. Radial symmetry2. Bilateral symmetry

Radial Symmetry• Imaginary plane can pass through a central

axis in any direction and body parts repeat around center of organism’s body

Bilateral Symmetry•Single plane can divide the body into

two equal halves.•Animals with bilateral symmetry have a

right and left side, front and back, top and bottom, and usually have segmented bodies.

Trend #3: Cephalization•Animals with bilateral symmetry have a

definite head.•Cephalization is the concentration of

sense organs and nerve cells in the anterior end (front end) of the body.

•Animals with this trait tend to respond in more complex ways to their environment.

Trend #4: Body Cavity Formation

•Most animals have a body cavity called a “coelom.”

•Fluid-filled space between the digestive tract and body wall

•Think of this as the area of your body where all of your major organs are located.

•Provides room for organs to grow and expand.

•Less complex animals do not have this area.

Types of Body Cavity • Acoelomate –

no body cavity,3 germ layers all packed

together, gut completely surrounded by tissues

•Pseudocoelomate – fluid-filled cavity between mesoderm and endoderm (separates gut and body wall)

•Coelom – fluid-filled cavity lined on both sides by mesoderm, found between muscles of body wall and muscles around gut

Trend #5: Embryo Development• In protostomes (worms, mollusks, and arthropods),

blastopore develops into mouth.• In deuterostomes (echinoderms and chordates), blastopore

develops into anus.• Three layers of embryonic cells (germ layers):

1. Endoderm – Develops into digestive and respiratory tracts.

2. Mesoderm – Develops into muscles, heart, sex organs, and kidneys.

3. Ectoderm – Develops into brain, sense organs, and skin.

Invertebrate Physiology (form and function)• To survive, all animals must perform the

same basic tasks (feed, digest, circulate nutrients, respirate, excrete wastes, reproduce, etc.)

• Each group of invertebrates has unique systems to help perform some of these tasks.

• We will study a variety of these systems amongst a variety of invertebrate groups.

Function #1 “Feeding and Digesting”

•All animals must feed and digest.•Two main methods of digestion:

1. Intracellular digestion. Food is digested inside of cells. Sponges mainly do this.

2. Extracellular digestion Food is broken down outside of cells in

special digestive organs. Simpler animals have only one opening

where food enters and waste leaves (two way digestive tract).

Complex animals have two separate openings a mouth and anus (one way digestive tract).

Two way vs. One way digestive tract

Mouth/Anus

Function #2 “Respiration”

•All animals must exchange O2 and CO2 with the environment.

•Structures range from gills lungs•All respiratory organs have two basic

features:1. Large surface area to come in contact

with air or water (the larger the better).

2. Organs must be moist (important for diffusion of gases across cells).

Function #3: “Circulation”•All cells in an animal must take in

oxygen/nutrients and give off CO2/waste.•Simple animals do this through diffusion

with their environment.•Complex invertebrates have hearts and

blood vessels.•There are two types of circulatory

systems:1. Open system2. Closed system

Open Circulatory System

•Common in arthropods.•Blood leaves the system (vessles)

Closed Circulatory System

•Blood stays within vessels.•Characteristic of larger,

more active animals.•More efficient form of

circulation.

Function #4: “Excretion”•All animals must control…

1. The amount of water in their cells.2. The amount of ammonia (NH3) that

builds up in the cells due to the breakdown of amino acids. Ammonia is poisonous to cells.

•The process of controlling these two things varies between aquatic and terrestrial invertebrates.

Excretion (cont.)

Aquatic Invertebrates

Terrestrial Invertebrates

• Sponge, cnidarians, and some worms.

• Excess ammonia and water is released through diffusion.

• Can use a variety of specialized structures to eliminate excess water and waste from cells.

• Ex.) Annelids = “Nephridia”▫Nephridia converts

ammonia to urine.

Function #5: “Response”

• Invertebrates show three trends in the evolution of their nervous systems:1. Centralization2. Cephalization3. Specialization

•Hydra (Cnidarian) No centralization, cephalization, or specialization

•Flatworm•More

centralized.•More

cephalized.•More

specialized.

•Arthropods.•Very centralized•Very cephalized•Very specialized

Function #6: “Movement and Support”•Most animals use muscles to move,

pump blood, and perform other life functions.

•Muscles usually work together with some kind of skeletal system (three different types);1. Hydrostatic skeletons – Muscles push

water. Common in cnidarians and worms.2. Exoskeletons – Outer skeleton made of

chitin. Common in arthropods.3. Endoskeletons – Inner skeleton. Common

in echinoderms and vertebrates.

Function #7: “Reproduction”

•Some animals can reproduce asexually during part of their life.1. Binary fission (splitting in two).2. Budding

•Most animals reproduce sexually during at least part of their life (requires sperm and egg).

•Male must fertilize the female.1. External fertilization2. Internal fertilization