Animals

Characteristics

The animal kingdom is divided into approximately 35

phyla with diverse species. However, all organisms in

the animal kingdom share these 6 characteristics

Eukaryotic

Lack cell walls

Multicellular

Heterotrophs

Motile (at some point in their life cycle)

Form a blastula (hollow ball of cells) during

embryological development

Evolution

Animals have a

similar

evolutionary

history to plants

that traces the

movement of

ancestral

organisms from

water onto land.

Evolution

Body Plans

Each species has a unique pattern and structure of body formation. The major phyla of animals have key characteristics to their body plans.

Levels of Organization

Cells are the simplest level of organization in animals but they can specialize to form tissues. Groups of tissues can form organs which can work together in organ systems

Evolution

Body Symmetry

The body symmetry of an animal can give indication of its classification, phylogeny, and function

Symmetry can be divided into three categories:

Asymmetrical – No symmetry at all

Radial symmetry – Symmetrical across a central axis and have no real front, back, or head

Bilateral symmetry – Symmetrical mirror image right and left sides. Generates the following distinctions:

Anterior and posterior (head and tail) ends

Dorsal and ventral (back and bottom/front) surfaces

Lateral (right and left) sides

Evolution

Evolution

Embryological Development

Animals reproduce through the formation of a

zygote when a sperm fertilizes an egg.

The zygote then divides until a hollow ball of cells

develops. This is the blastula.

Cells will start infolding a one spot in the ball,

forming a tube that connects both ends. This

eventually develops into the digestive tract.

The hole formed where the infolding began is

known as the blastopore. This can develop into

either the mouth or the anus.

If it develops into the mouth, the animal is a

protostome

If it develops into the anus, the animal is a

deuterostome

Evolution

Segmentation: Repeating parts

Many animals demonstrate segmentation which is

the dividing of the body

into segments.

Examples: Earthworms

and other insects

Limbs: Legs, Flippers, and Wings

Animals with bilateral symmetry tend to have paired

limbs and cephalization (development of a distinct

head with sense organs)

Examples: antennae, mouthparts, wings, gills, legs,

fins, arms

Concept Check

What characteristics do all animals have?

What types of symmetry are found in animals?

Describe the embryological development of an

animal. Include the terms zygote, blastula,

protostome, and deuterostome in your answer.

Invertebrates Greater than 98% of animals are invertebrates

Invertebrates are animals that lack a backbone

Vertebrates

Vertebrates are animals with a scull and a

backbone, which is composed of segments known

as vertebrae

We are mostly familiar with vertebrates because

they are the animals with which we commonly

associate

E.g. pets (cats, dogs, reptiles, birds), livestock (cows,

pigs, sheep), etc.

Vertebrates include fish, amphibians, reptiles, birds,

mammals, and humans.

Evolution of Vertebrates

The evolutionary relationships between vertebrates are

shown on the next slide

This was constructed using a combination of anatomical,

molecular, and fossil evidence.

The branching points show the evolution of major

derived traits.

Hinged jaws – wider variety of prey

Lungs – buoyancy and possible ability to breathe on land

Tetrapod – four-footed for land motility

Amniotic egg – waterproof egg with shell for reproduction

on land

Feathers – modified scales as insulation for heat

conservation

Concept check

Which phylum has the simplest animal?

What two general categories are often used to

classify animals? What is the main difference that

divides these categories?

What are three evolutionary steps in vertebrates?

What is the significance of each?