Characteristics of Animals Chapter 25

General Characteristics of Organisms Found in the Animal Kingdom Animals are eukaryotic, multicellular, heterotrophic organisms.

Not all animals have the ability to move to find food or capture their prey. Organisms that are permanently attached to a surface are known as sessile.

Digestion in Animals Once food has been ingested it must be digested. Some organisms do not have a complete digestive tract. Their food enters and waste exits through the same opening.

Fertilization Most animals reproduce sexually. Fertilization of egg cells may be internal or external. -internal -External

The 3 Embryonic Germ Layers of Animal Development Most animals develop from a fertilized egg cell called a zygote.

Once fertilization has occurred, the zygote begins rapidly dividing. A blastula is the hollow fluid filled ball of cells that is the result of the cell division of the zygote. A gastrula is the structure that forms from a blastula as the cells on one side move inward forming an opening. During gastrulation a third layer of cells is added to most embryos known as mesoderm.

Germ Layers Form the tissues, organs, & systems of an animal Ectoderm (outer) forms skin, nerves, & sense organs Endoderm (inner) forms the digestive & respiratory organs & systems Mesoderm (middle) forms muscles, circulatory system, reproductive & excretory systems

protostomes In animals where the opening of the gastrula develops into the mouth are known as protostomes. (snails, earthworms, and insects)

Deuterostomes Animals that develop a mouth from cells in the gastrula rather than the opening are called deuterostomes. (fish, birds, and humans)

3 Forms of Symmetry in Animals Symmetry describes the arrangement of body structures of animals. (Asymmetry, Radial, Bilateral) Asymmetry -If an animal has an irregular shape or no symmetry to its body plan.

Radial Symmetry Animals that can be divided along any plane, through a central axis, into equal halves.

Bilateral Symmetry Animals that can be divided lengthwise into equal right and left halves.

Anatomical Directional Terms Ventral = the belly or under side of an animal Dorsal = the back or top side of an organism Anterior = towards the head end Posterior = towards the tail end or away from the head Proximal = towards the body where an appendage joins the body Distal = away from the body towards the end of an appendage Caudal = synonym for posterior Cranial = relating to the skull or cranium

Anatomical Directional Terms

Anatomical Directional Terms

Body Plan Body cavities are fluid-filled spaces inside an organism where the internal organs are often found. 1) Acoelomate = the simplest body plan, 3 germ layers but no body cavity 2) Pseudocoelomate = has a fluid-filled body cavity between endoderm and mesoderm = pseudocoelom The internal organs are actually found free within pseudocoelom 3) Coelomate = has body cavity & specialized organs that develop in coelom Found in humans, insects, fishes

3 Animal Body Plans 1) Acoelomate = animals that develop from the 3 cell layers but have no body cavities. They have a digestive tract throughout their body Ex. Flatworms

3 Animal Body Plans 2) Pseudocoelomate = animals with a fluid filled body cavity that is partially lined with mesoderm They have a one-way digestive tract with regions of specific functions Ex. Earthworms

Pseudocoelomate

3 Animal Body Plans 3) Coelomate = animals that have a true fluid filled body cavity completely surrounded by mesoderm that contains internal organs They have internal organs and a digestive tract attached by mesoderm and suspended within the coelom Ex. Humans and Fish

Coelomate

Ectotherm Vs. Endotherm Ectothermic- animal that has a variable body temperature and derives its heat from external sources. Ex) Snake Endothermic- Animal that maintains a constant body temperature and is not dependant on environmental temperature. Ex) Cat

Ectothermic

Endothermic