Overview of Animal Diversity

LEARNING OUTCOMES Understand how the animals are organized and how this organization is different from that of plants, fungi, protists, and prokaryotes. Compare and contrast Parazoa and Eumetazoa in terms of evolution, complexity, symmetry, and organization of embryonic cell layers. Compare and contrast asymmetry, radial symmetry, and bilateral symmetry. Differentiate among acoelomate, pseudocoelomate, and coelomate organisms; indicate how they are evolutionarily related and give examples of each.

Differentiate between protostomes and deuterostomes.

General Features of Animals Animals are the consumers of the Earth They are a very diverse group -However, they share major characteristics -Are heterotrophs -Are multicellular -Have cells without cell walls -Most are able to move

General Features of Animals -Are very diverse in form and habitat -Most reproduce sexually -Have a characteristic pattern of embryonic development -Cells of all animals (except sponges) are organized into tissues

Evolution of the Animal Body Plan 1. Tissues 2. Symmetry 3. Body cavity 4. Development

Evolution of the Animal Body Plan Evolution of tissues Metazoans are divided into two main branches: -Parazoa (Sponges - the simplest animals) lack defined tissues and organs -Have the ability to disaggregate and aggregate their cells -Eumetazoa (all other animals) have distinct and well-defined tissues -Have irreversible differentiation for most cell types

Evolution of the Animal Body Plan 2. Evolution of symmetry -Sponges also lack any definite symmetry -Eumetazoa have a symmetry defined along an imaginary axis drawn through the animal’s body -There are two main types of symmetry

Evolution of the Animal Body Plan -Radial symmetry -Body parts arranged around central axis -Can be bisected into two equal halves in any 2-D plane -Bilateral symmetry -Body has right and left halves that are mirror images -Only the sagittal plane bisects the animal into two equal halves

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Evolution of the Animal Body Plan Bilaterally symmetrical animals have two main advantages over radially symmetrical ones 1. Cephalization -Evolution of a definite brain area 2. Greater mobility

Evolution of the Animal Body Plan 3. Evolution of a body cavity -Eumetazoa produce three germ layers -Outer ectoderm (body coverings and nervous system) -Middle mesoderm (skeleton and muscles) -Inner endoderm (digestive organs and intestines) Body cavity = Space surrounded by mesoderm tissue that is formed during development

Diploblastic vs. Triploblastic – Cell Layers Diploblastic – two cell layers Ectoderm – outer layer Endoderm – inner layer The Radiata Triploblastic – three cell layers Ectoderm, endoderm Mesoderm – layer between ectoderm and endoderm The Bilateria Ectoderm – outer covering of the body; nervous system Endoderm – digestive organs and intestines Mesoderm – skeleton and muscles

Evolution of the Animal Body Plan 3. Evolution of a body cavity -Three basic kinds of body plans -Acoelomates = No body cavity -Pseudocoelomates = Body cavity between mesoderm and endoderm -Called the pseudocoel -Coelomates = Body cavity entirely within the mesoderm -Called the coelom

Evolution of the Animal Body Plan -The body cavity made possible the development of advanced organs systems Pseudocoelomates use pseudocoel for circ. Coelomates developed a circulatory system to flow nutrients and remove wastes -Open circulatory system: blood passes from vessels into sinuses, mixes with body fluids and reenters the vessels -Closed circulatory system: blood moves continuously through vessels that are separated from body fluids Why do you think closed is more advanced?

Evolution of the Animal Body Plan 4. Evolution of different patterns of development -The basic Bilaterian pattern of development: -Mitotic cell divisions of the egg form a hollow ball of cells, called the blastula

Evolution of the Animal Body Plan Bilaterians can be divided into two groups: -Protostomes develop the mouth first from or near the blastopore -Anus (if present) develops either from another region of embryo -Deuterostomes develop the anus first from the blastopore -Mouth develops later from another region of the embryo

Embryonic development in protostomes and deuterostomes Coelom Archenteron Mesoderm splits Mouth forms from blastopore Mouth Coelom Anus Mesoderm Blastopore Blastula Coelom Archenteron Archenteron outpockets to form coelom Mouth Coelom Anus Anus forms from blastopore Blastopore Blastula Deuterostomes