Characteristics of Animals

3 types of symmetry Asymmetry: No symmetry Bilateral Symmetry: One line of symmetry Radial Symmetry: More than one line of symmetry

1. What type of Symmetry?

2. What type of Symmetry?

3. What type of Symmetry?

Characteristics of Animals A. Multicellular with no cell wall B. Heterotrophs- method of getting food may vary C. Many different types of motility D. Animals must digest food- break food down.

Development of animals A. Most animals develop from a single fertilized egg called a zygote.

Stages of Development 1. Cleavage: Division of the unicellular egg into two cells 2. Blastula: Cell division proceeds until a hollow ball of cells forms 3. Gastrula: formed when the cells of the blastula fold inward- two cell layers:

a. The ectoderm (outer layer) will develop into the skin and nervous tissue b. The endoderm (inner layer) develop into the lining of the animal’s digestive tract c. Blastopore: opening of the gastrula

4. Mesoderm (middle) develops between the endoderm and ectoderm 4. Mesoderm (middle) develops between the endoderm and ectoderm. This layer gives rise to muscles, reproductive organs, circulatory vessels 5. As the cells begin to develop embryo changes shape and becomes specialized to perform different function.

1. Protostome: an animal with a mouth that develops from the blastopore Most invertebrates 2. Deuterostome: an animal with an anus that develops from the blastopore. Mouth develops from cells elsewhere. Echinoderms and vertebrates

Other animal characteristics A. Cephalization: the concentration of sense organs and nerve cells at the anterior end of the body - Most obvious in animals with bilateral symmetry

Body Cavity Body cavity: Fluid-filled spaces between the digestive tract and the body wall • Importance: provides a safe space for internal organs

Acoelom: no body cavity - Example: flatworm Pseudocoelom: body cavity only partially lined with mesoderm - Example: roundworm Coelom: full body cavity - Example: earthworm