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 Bilateral Symmetry Radial Symmetry Posterior end Dorsal side Anterior end Plane of symmetry Planes of symmetry

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 Body covering Tissue-filled region Digestive tract (a) No body cavity Body covering Coelom Muscle layer Body covering Pseudo- coelom Digestive tract Tissue layer lining coelom and suspending internal organs Digestive tract (b) Pseudocoelom (c) True coelom

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