Introduction to the Animal Kingdom

Introduction to the Animal Kingdom

• Animals are multicellular eukaryotic heterotroph whose cells lack cell walls, digestion is internal

• Vertebrates: 5% of animal species with backbones

• Invertebrates: 95% of animal species WITHOUT backbones

• Cell specialization – special shape, physical structure, and chemical composition to perform a special function in a multicellular organism (Division of Labor)

Early Development

• Zygote (fertilized egg) undergoes divisions to form blastula, or a hollow ball of cells

• Blastula flattens on one side and folds into itself forming a single opening called a blastopore

• Blastopore leads into center tube running the length of the developing embryo. This tube becomes the digestive track– Protostome – mouth formed first from blastopore

(most invertebrates)– Deuterostome – anus formed first from blastopore

(echinoderms and all vertebrates)

Early Development (continued)

• Cells then differentiate into three layers, called germ layers– Endoderm – innermost germ layer – forms

linings of digestive track and respiratory system

– Mesoderm – middle germ layer – forms muscles, circulatory, reproductive, and excretory systems

– Ectoderm – outermost germ layer – forms sense organs, nerves, and outer layer of skin

Early Development (continued)

In Order to Survive, Animals Must:

• Feed – – Carnivores – eat other animals– Herbivores – eat plants– Omnivores – eat other animals and plants– Parasites – inside or on other organisms and

do them harm– Filter feeders – strain food from water– Detritus feeders – feed on dead organic

matter

In Order to Survive, Animals Must:

• Respire – – Consume oxygen and give off CO2

– Skin, gills, lungs

In Order to Survive, Animals Must:

• Circulate/Internal Transport – – Must carry O2, nutrients and waste products to

and from internal cells– Heart and blood vessels in larger animals– Smaller animals rely on diffusion

In Order to Survive, Animals Must:

• Excrete – – Small animals – diffusion– Larger animals – excretory systems (that can

include complex kidneys)

In Order to Survive, Animals Must:

• Respond – – Nerve cells – brain– Gather information from environment– Varies greatly from phylum to phylum

In Order to Survive, Animals Must:

• Move – – Sessile – one spot, no movement– Motile – move, muscles and/or skeletons

In Order to Survive, Animals Must:

• Reproduce – – Mainly sexual, but invertebrates can also

reproduce asexually– Live birth or eggs– Direct Metamorphosis – young look like adult– Indirect Metamorphosis – young →

metamorphosis → adult

Direct Metamorphosis

– Direct – young look like adult

Indirect Metamorphosis• Indirect – young → metamorphosis → adult

Early Animals and the Cambrian Explosion

– Scientists hypothesize that animals evolved from a colonial flagellated protist.

– The oldest animal fossils found are 550–575 million years old.

– The molecular data suggest a much earlier origin for animals.

Early Animals and the Cambrian Explosion

– Animal diversification appears to have accelerated rapidly from 525-535 million years ago, during the Cambrian period.

– Because so many animal body plans and new phyla appear in the fossils from such an evolutionarily short time span, biologists call this episode the Cambrian explosion.

Early Animals and the Cambrian Explosion

– The Cambrian explosion may have been ignited by

• increasingly complex predator-prey relationships and/or

• an increase in atmospheric oxygen.

– The genetic framework for complex bodies, a set of “master control” genes, was already in place.

Animal Evolution• Complex animals tend to have high levels of cell

specialization and internal body organization, bilateral body symmetry, a front end, or head, with sense organs, and a body cavity.

Cell Specialization

• Cell → tissue → organ → organ system → organism– Ex. Stomach cell → stomach tissue →

digestive system (mouth, stomach, intestines, etc) → all organ systems put together

Body Symmetry

• Asymmetrical – no symmetry (sponges)• Radial symmetry – body parts repeat around

center of body (simple animals – sea anemone and starfish)

• Bilateral symmetry – body can be divided into two equal halves – left and right sides– Anterior – front end– Posterior – back end– Dorsal – upper side– Ventral – lower side

Body Symmetry

Radial SymmetryBilateral Symmetry

Planes ofsymmetry

Plane ofsymmetry

Dorsal side

Posterior end

Anterior end

Body Cavity– Animals also vary according to the presence

and type of body cavity, a fluid-filled space separating the digestive tract from the outer body wall.

– There are differences in how the body cavity develops.

• If the body cavity is not completely lined by tissue derived from mesoderm, it is called a pseudocoelom.

• A true coelom is completely lined by tissue derived from mesoderm.

Body Cavity

(a) No body cavity

(b) Pseudocoelom (c) True coelom

Digestive tract

Bodycovering Tissue-filled

region

Body covering

Musclelayer

Pseudo-coelom

Digestive tractDigestive tract

Coelom Bodycovering

Tissue layer liningcoelom andsuspendinginternal organs

Cephalization

• Complex animals concentrate sense organs and nerve cells in the anterior end of the body, this is called cephalization– Ganglia – small clusters of nerve cells (simple

animals)– Brain – clusters of ganglia (more complex

animals)

Introduction to Invertebrates