1. Sponges, Cnidarians, and Unsegmented Worms Chapter 26

2. Bilateral Symmetry The picture on the left demonstrates bilateral symmetry. This is when the left side of the body when split directly down the middle in a longitudinal line would be a mirror image of the right side of the body.

3. Radial Symmetry The picture on the right displays radial symmetry. This is when the organism is split into equal parts that are all the same. Each part connects at a central point.

4. Sponges The first sponges date back to the beginning of the Cambrian Period (approximately 580 million years ago!) Most sponges live in the sea however some do live in fresh water. Although sponges are multicellular animals they differ from most other animals.

5. Cnidarians

6. Classification of Cnidarians The cnidarians include the classes scyphozoa, cubozoa, and anthazoa The jellies (jellyfish) are classes scyphozoa and cubozoa The corals and anemones, however, are class anthazoa. The corals and anemones have no medusa stage, only polyps, where the jellyfish are in a longer medusa stage, with a shorter polyp stage

7. Life Cycle of Cnidarians

9. The Jellies

10. Class Scyphozoa Jellyfish are from the class scyphozoa Go through the same lifecycle as the hydrozoans Some jellies, such as the lions mane (as shown left) grow up to 2 meters in diameter!

11. Sea Anemones and Coral

12. Coral and sea anemones are included in the class anthozoa This class only has the polyp stage of the life cycle The adults reproduce sexually, however many anthozoans also reproduce asexually

14. Flatworms Flatworms belong to the phylum platyhelminthes The flatworms are the simplest animals that have bilateral symmetry Although flatworms are generally only a few millimeters thick they can be up to 20 meters long Many flatworms are parasitic

15. Planarians Planarians are free living flatworms belonging to class tubellaria They are usually less than 1cm in length they can reach lengths of 60cm or more

16. Flukes Flukes belong to the class trematoda They are parasitic flatworms and although some are external parasites most are internal parasites, including the ones that affect humans Flukes are mostly hermaphrodites, they undergo sexual reproduction in a similar way to the free- living flatworms People infected with flukes generally get very sick and often die

17. Tapeworms Tapeworms are members of the class cestoda They attach to intestinal walls of humans as well as other animals and absorb food that the host has already digested for them They can be up to 18 meters long

18. Round Worms Round worms belong to phylum nematoda They are one of the simplest animals to have a two opening digestive system, having both a mouth and an anus They can be microscopic or a meter long They can be either free-living or parasitic Like flatworms they breath and excrete through their body walls