1. Video Crash Course: Simple Animals

2. Invertebrate Evolution
Essential Question: what are the major trends in invertebrate evolution?

3. The first multicellular animals
Invertebrate fossils date back between 575 and millions of years ago
Distinctive flat, plate-shaped
Showed little cell specialization or cephalization
Lived in shallow seas and some may have had photosynthetic algae living within them

4. Beginnings of invertebrate diversity
A few million years later (Cambrian Period) radically different invertebrates
Some animals developed shells, skeletons, and other hard body parts, providing a wealth of fossils
Ancestors of most modern animal phyla first appeared

5. Feeding and digesting
Simpler animals break down food primarily through intracellular digestion (food digested inside the cells)
Ex. Sponges
Complex animals use extracellular digestion (food broken down outside of cells and then absorbed into the body)
Ex. Mollusks, annelids, arthropods, and echinoderms
Flatworms and cnidarians use both

6. Feeding and digesting
Cnidarians and most flatworms ingest and expel waste through the same opening
Complex animals digest food in a digestive tract and expels waste through the anus
Specialization of the digestive tract allows food to be process more efficiently

7. Respiration
Respiratory organs have large surface areas that are in contact with the air or water.
For diffusion to occur, the respiratory surface must be moist
Many simple aquatic animals respire through their skin.

8. Respiration
Complex aquatic animals develop gills (rich in blood vessels that brings blood close to the surface for gas exchange)
Terrestrial animals have respiratory surfaces covered in either water or mucus as well as having the air moistened as it travels through the body

9. Invertebrate Evolution II
Essential Question: How do different invertebrate phyla carry out life functions?

10. Circulation
Most complex animals move blood through their bodies using one or more hearts
Open circulatory systems- blood is only partially contained within a system of blood vessels. One or more hearts pump blood through blood vessels into a system of sinuses or sponge cavities
Ex. arthropods and most mollusks

11. Circulation
Closed circulatory systems- Heart or heart-like organs forces blood through vessels that extend throughout the body. Blood is kept at a high pressure and is more efficient than open circulatory systems
Ex. Annelids and some mollusks

13. Excretion
Aquatic invertebrates diffuses ammonia from their body tissues into the surrounding water
Terrestrial invertebrates must conserve water so they convert ammonia into a compound called urea which is eliminated through urine

14. Response (Nervous system)
Nerve net- simplest nervous system found in cnidarians that consists of individual nerve cells in a netlike arrangement throughout the body
Centralized- in flatworms and roundworms, the nerve cells are more centralized in small clumps in the head
Cephalization- in cephalopod mollusks and arthropods, the nerve cells (ganglia) are organized into a brain that controls the nervous system

16. Response (Nervous system)
Complex animals may have a variety of specialized sensory organs that can detect light, sound, chemicals, movement, and even electricity
Ex. Flatworms have simple eyespots that detects the presence of light while arthropods have eyes that can detect motion and color, and can forms images

17. Movement and support
Hydrostatic skeletons- muscles surround a fluid-filled body cavity that supports the muscles
Ex. Annelids and certain cnidarians
Exoskeletons- an external skeleton made of chitin in which muscles are attached inside the hard body
Ex. Arthropods and shelled mollusks
Endoskeletons- a structural support inside the body
Ex. Echinoderms

18. Reproduction
Most invertebrates reproduce sexually, however depending on favorable environmental factors, many may also reproduce asexually (faster than sexually)
Hermaphrodites- individuals that produce both sperm and eggs
Ex. Earthworms