Chapter 26

Introduction to Animals

Characteristics of Animals There are 3 general features of animals which all animals share: All animals are multicellular. All animals are heterotrophs. All animal cells lack cell walls.

Characteristics of Animals Another feature most animals share is that they are mobile.

Certain animals, however, such as sponges and corals are immobile.

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Two Main Classes of Animals

Animals fall into one of two categories: Invertebrates-animals that lack a backbone.

The vast majority of animals are invertebrates.•Sponges•Ants•Squid

Vertebrates-animals with a backbone.•Cats, Dogs, Birds •Fish, Frogs, Turtles•Humans

Invertebrates

On land, these are usually very small because they do not have an internal skeleton for support.

They assist with the pollination of plants and the decomposition and recycling of dead material in an ecosystem.

Vertebrates Vertebrates have a cranium and an internal skeleton composed of bone or cartilage.

Their vertebra protect the nerve cord and provide a site for muscle attachment.

Animal Body Systems An animal’s skeleton provides a framework that supports the animal’s body.

There are three main types: Hydrostatic-a water filled cavity under pressure.

Think jellyfish.

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Animal Body Systems Exoskeleton-a rigid external skeleton encasing the body of the animal. Think lobsters.

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Animal Body Systems Endoskeleton-a rigid internal skeleton. Think humans.

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Digestive and Excretory Systems

The digestive system extracts energy and nutrients from an animal’s food. Some animals have a gastrovascular cavity with a single opening allowing food in and out.

Other animals have a one-way digestive tract with two openings. The food moves in through the mouth, and out through the anus.

Digestive and Excretory Systems

The excretory system removes wastes from the animal’s body. Most of these wastes are produced as a result of cellular metabolism.

Ammonia is a main waste that needs to be removed.

Animals have to remove waste products and maintain an internal osmotic balance.

Nervous Systems The nervous system carries information about the environment through the body and coordinates a response.

There are two main types: Simple Complex

Simple Nervous Systems Nerve nets have no complex arrangement. There is no coordinated response to stimuli. Jellyfish and hydras.

Simple Nervous Systems Other animals have clusters of nerve cells called ganglia which can coordinate responses to stimuli. Flatworms.

Complex Nervous Systems These animals have true brains with sensory structures.

These animals can have high level interactions with their surroundings. Grasshoppers, humans, dolphins.

Respiratory Systems This system is responsible for exchanging O2 and CO2 between the organisms and the environment.

Some animals have gills that allow for gas exchange in the water.

Other animals have lungs that allow for exchange on land.

Circulatory System This system transports gases, nutrients, and other substances within the body. Open circulatory systems-have a heart that pumps the O2/nutrient rich fluid through the body to feed the tissues and cells.

Closed circulatory systems-have a heart that pumps blood through a system of vessels.

Reproduction Reproduction is important for the survival of a species.

There are two main strategies: Asexual Sexual

Each one has unique advantages and disadvantages.

Asexual Reproduction Advantages

No need to find a mate.

Disadvantages Little, if any, genetic diversity One disease/illness could potentially wipe out a species.

Sexual Reproduction Advantages

High variety within the genome. Not as susceptible to disease.

Disadvantages Need to find a mate.

Body Plans Animals body plans describe the animal’s shape, symmetry, and internal organization.

The cells of all animals except sponges are arranged into units called tissues.

Tissues are groups of cells that carry out a specific function.

Tissues are often organized into organs which perform specific jobs.

Body Symmetry Body symmetry describes how an animal’s body can be divided into similar pieces. Asymmetry describes an animal that cannot be divided into similar pieces.

Radial symmetry describes animals whose symmetry revolves around a central axis.

Bilateral symmetry describes an animal that has right and left sides which are mirror images of each other.

Embryonic Development The diploid zygote is the first stage of the new individual.

Cell division makes up the second stage of development. The zygote does not increase in size.

Embryonic Development Eventually a blastula, which is a hollow ball of cells is formed.

Embryonic Development After the blastula has formed, one side of the organism begins to pinch inward to form the gastrula.

The structure is called the blastopore.

Developmental Patterns Eventually the blastopore reaches the other side of the organism and a second opening forms.In protostomes, the

first opening becomes the mouth.

Clams, snails, earthworms, insects

In deuterostomes, the first opening becomes the anus.

Sea stars and vertebrates

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Cell Differentiation During gastrulation, the cells of the gastrula begin increasingly different from one another.

Cell Differentiation This leads to the formation of the three main tissue types: Endoderm-forms the gut, respiratory system, many glands.

Mesoderm-forms most of skeleton and muscles, circulatory system, excretory organs.

Ectoderm-outer layer forms the skin, nervous system.

Body Cavities Once the tissue layers start to form and development continues, body cavities start to form.

Body Cavities A coelomate has a body cavity surrounded by mesoderm.

A pseudocoelomate has a body cavity, but it is not lined by mesoderm.

An acoelomate has no body cavity.

Characteristics of Chordates

At some point during development, all chordates have a dorsal nerve cord, a notochord, pharyngeal pouches, and a post anal tail.

Characteristics of Chordates

Most chordates are vertebrates. Tunicates and lancets are invertebrate chordates and represent an evolutionary link between vertebrates and invertebrates.

The First Vertebrates The first vertebrates evolved about 500 million years ago.

They were essentially a fish-like animal with a cartilaginous skeleton rather than a bony skeleton.

Very primitive and they lacked many of the features we think of today when we think of vertebrates--backbones and jaws.

Fish Evolution Two features evolved in fish that set them apart from the early vertebrates: Jaws and paired fins.

These fish also had hardened spines. The jaws allowed for grasping prey. Fins allowed for fast swimming in pursuit of prey.

These fish were replaced by sharks and bony fishes.

Fish Are… The most primitive vertebrates. Share the following key characteristics: They have endoskeletons, gills, closed-loop circulation, and kidneys.

They also have swim bladders, fins, and lateral lines.

Animals that gave rise to amphibians.

Amphibian Evolution

Early amphibians were poor swimmers and were not like frogs and toads of today.

As competition from predators increased, the numbers of species and the diversity of amphibians increased.

Amphibian Evolution There are three characteristics that helped amphibians succeed on land: Lungs-enabled the exchange of gases out of the water.

Heart-a more efficient way of delivering O2 to the body than a fishes heart.

Strong limbs-easy movement from place to place.

Amphibians need to keep their skin and eggs moist. They live in and around water.

Amphibians Are… The first vertebrates to live on land. They contain legs, lungs, double-loop circulation, a partially divided heart, and cutaneous respiration.

They are tied to the water for reproductive purposes.

Animals that gave rise to reptiles.

Evolution of Reptiles To make the complete move to land, vertebrates needed adaptations to allow them to do so.

The watertight amniotic egg was an adaptation that allowed reptiles to move away from the water. An amniotic egg contains yolk and a shell.

Evolution of Reptiles The first reptiles have two important evolutionary adaptations: Watertight, scale covered skin. Amniotic egg.

These adaptations allow reptiles to deal with dry conditions.

The first reptiles were small dinosaurs that evolved from amphibians.

Reptiles Are… Reptiles are animals with scales, clawed toes, and ectothermic metabolism. Reptiles lack hair or feathers.

Dinosaurs were reptiles. Snakes, crocodiles, turtles, turata and lizards are examples of reptiles.

Animals that gave rise to birds and mammals (from therapsids). http://eatmorecookies.files.wordpress.com/2008/08/tuatara-on-forest-floor-three-quarters.jpg

Evolution of Birds Birds evolved from meat eating dinosaurs.

They had skeletons that were very much like dinosaurs.

The Archaeopteryx fossil (about the size of a crow) represents an intermediate form of a bird between the dinosaurs and modern birds.

Archaeopteryx Had long teeth, arms with fingers and claws.

It lacked a breastbone to anchor flight muscles.

It had solid bones instead of hollow ones.

It had feathers on its wings and a tail, a wishbone (fused collarbone).

Birds Are… Animals that lay amniotic eggs, have scales that cover their legs and feet, have feathers, endothermic metabolism, a beak, a lightweight skeleton, and lungs with air sacs.

Evolution of Mammals Early mammals were about the size of mice, kept down by the dinosaurs.

After the dinosaurs and other large marine reptiles died out, mammals increased in size, took to the oceans and came to be the dominant life forms of today.

Mammals There are three types of mammals:

Monotremes - lay eggs which quickly hatch.

Marsupials - give birth to live young that crawl into a pouch to complete their development.

Placental Mammals - give birth to live young that may or may not require extended care.

All three reproduce by internal fertilization.

Mammals Are… Animals that evolved from mammal-like reptiles called therapsids.

Have an endothermic metabolism, mammary glands, specialized teeth, body hair.