Characteristics:

• Eukaryotic

• Don’t have cell walls

• Ingest/digest food

• mobile

• Reproduce sexually and produce an embryo that undergoes a state of development

Characteristics Used to Classify Animals

Levels of Organization:

• Classified based on the differences in their tissues and organ systems

• Most animals have cells that are organized into tissues (except sponges)

  • Tissue: a group of similar cells that perform a specific function (organized into organs and organ systems)

Number of Germ Layers:

• Most animal have three layers

  • Ectoderm- Outer Layer, (skin, nerve tissue, sense organs)

  • Mesoderm- Middle layer (muscles, blood, kidneys, reproductive organs)

  • Enderm- inner layer (lungs, liver, pancreas, bladder, stomach lining)

• Classified based on whether they have 123 germ layers

Symmetry and Body Plans:

• Asymmetrical Body Plans: body is an irregular shape eg. sponges

• Symmetrical body plans: radial symmetry can be divided along any plane into roughly equal halves

• Bilateral symmetry: Can be divided along one plane into 2 equal halves

Body cavities:

• Coelum: fluid-filled body cavity that provides space for the development and suspension of organs and organ systems.

  - organs are contained in the body cavity

• Can be:

  • coelomate: have

  • Acoelomate: without

  • pseudocoelomate is similar to coelom but lacks a layer of cells

• Advantages: allows for quick responses and movement and development of complex organs

Digestive system:

• No digestive system (sponges)

• Incomplete digestive system: only one opening, food goes in and waste comes out of the same hole

• Complete digestive system: digestive tube has 2 openings

• Protostome: mouth develops first

• Deuterostome: anus develops first

Segmentation:

• The division of the body into repetitive segments or sections

• Advantages: If one section is damaged, the rest continue to work. Mobility is also more effective

Movement:

• Most animals are mobile

• Sessile: some animals are stationary and stay in one place, but at some point in its early stages it had movement

Reproduction:

• Reproduce sexually

• produced by either external or internal fertilization

  • External: fertilization happens outside of the body

  • Internal: Gameters combine inside the body

*some animals like aphids reproduce sexually/asexually

Nervous System:

• Some have it, some don’t

• Cephalization:

  • nervous tissue is concentrated at one part of an organism (eg. the brain)

  • Ceph: means brain