Introduction to Animals

General Characteristics All animals are heterotrophic Different digestive systems Animals are either invertebrates or vertebrates Body variations allow animals to live in a diverse range of habitats Cells are organized into tissue, that is specialized to perform a specific function

Reproduction Hermaphrodites: organism that produces both eggs and sperm in the same body (earthworms) Zygote: when sperm penetrates egg to form a fertilized egg External Fertilization: egg and sperm combine outside the animal’s body (fish) Internal Fertilization: sperm and egg combine inside the animal’s body

Development Endoderm Cells: develop into digestive organs and the lining of digestive tract Ectoderm Cells: Nervous tissue and skin Mesoderm Cells: Muscle tissue, circulatory system, excretory system, and sometimes respiratory system Human Development

Symmetry Symmetry describes the similarity or balance among body structures of organisms Assymmetrical: Irregular shape and has no symmetry or balance in its body structure Radial: Can be divided along any plane through a central axis into roughly equal halves Bilateral: Can be divided into mirror image halves only along one plane through a central axis Cephaliztion: animals with bilateral symmetry also have an anterior, or head end, and a posterior, or tail end & dorsal (back), ventral (front).

Body Cavities Coelomates: Tissue formed from the mesoderm that lines and encloses the organs in the coelom - Coelom: Huge adaptation in evolution of larger and more specialized body structure. Pseudocoelmates: Fluid-filled cavity that develops between the mesoderm and the endoderm rather than developing entirely within the mesoderm as in coelomates. Acoelomates: Animals that do not have a coelom. Have solid bodies, without a fluid filled body cavity between the gut and the body wall.

Segmentation Important feature in the evolution of coelomate animals. Two Advantages of Segmentation: 1)Segmented animals can survive damage to one section and still live because other sections may be able to carry out the function 2)Movement is more effective since each segment moves independently