2.  About 97% of all animals are invertebrates.  Invertebrates are animals which do not have a backbone.  There are nine phyla of invertebrates: Porifera, Cnidaria, Platyhelminthes, Nematoda, Rotifera, Mollusca, Annelida, Arthropoda, & Echinodermata.

3.  The phylum Porifera are sponges.  There are about 800 different species of sponges, and 88% are marine.  Freshwater sponges are smaller and less brightly colored than marine sponges.

4.  Sponges are filter feeders.  This means that they use their body as a filter to trap their food, microscopic plankton.  Sponges are asymmetrical and live attached to one spot as adults making them sessile animals.  Sponges have a skeleton composed of a flexible protein material called spongin & hard fibers called spicules composed of calcium carbonate or silicon dioxide.

5.  The body of a sponge is filled with holes or pores through which water enters their hollow bodies.  Sponges lack the tissue level of organization but they do have some specialized cells.  Choanocytes are specialized cells that line pores in a sponge and have a flagellum that spins to pull in water and food.

6.  Collar cells at the base of choanocytes capture plankton & start digesting it.  Amebocytes are specialized cells that carry food to all other parts of a sponge's body.  Wastes and excess water leave a sponge through an opening at the top called the osculum.

7.  Sponges reproduce asexually by internal or external buds and by fragmentation.  Each piece can form a new sponge.  This is how sponges form colonies.

8.  Sponges are hermaphrodites that produce both eggs and sperm.  They do not fertilize their own eggs, but they exchange sperm with other sponges.  Sponges reproduce sexually by dispensing eggs and sperm into the water.

9.  If the freshwater supply evaporates, freshwater sponges become dormant and form an internal bud or gemmule [jem-yool] which is released when the sponge dies.  The gemmule is a small freshwater sponge covered with hardened mucus which prevents it from drying out.  When the freshwater returns, the gemmule becomes an active sponge.

10.  The phylum Cnidaria include sea anemones, hydra, corals and jellyfish.  All Cnidaria are marine except hydra, which is a freshwater organism. Sea anemone

11.  Cnidarians have radial symmetry and are carnivorous using tentacles that surround their mouth to get food.  Cnidarians exhibit two body forms - the sessile polyp with tentacles & mouth at the top or the motile medusa with tentacles & mouth on the bottom.  Cnidarians may exist in one of these two stages or go through both stages in their life cycle such as the jellyfish. Hydra

13.  Cnidarians have 2 layers of cells --- gastrodermis & epidermis.  Cnidarians have a hollow gastrovascular cavity on the inside lined with gastrodermis.  Epidermis covers the outside and a jellylike material called mesoglea is between the layers.  Mesoglea is thin in polyp forms but thick in medusa forms. Coral

14.  Cnidarians have stinging cells called nematocysts or cnidocytes on their tentacles that are poisonous & shoot out like a harpoon to kill or paralyze prey.  Their mouth is the only opening to their body so they have a two-way digestive system. They also have a simple nerve net.

15.  Cnidarians reproduce asexually by budding or sexually producing fertilized eggs whenever males release sperm and females release eggs into the water.  Some cnidarians like coral build a limestone case that makes an underwater reef.

16.  The phylum Platyhelminthes are dorsoventrally flattened and have a definite anterior and posterior end giving them bilateral symmetry.  Their bodies are solid so they are said to be acoelomate [ey-see-luh- meyt]. Fluke

17.  Some flatworms are parasites, while others are free-living carnivores or scavengers.  Examples of parasitic flatworms are flukes and tapeworms.  Flatworms also have only a mouth for both food and wastes. Tapeworm

18.  Their nervous system is composed of a nerve net and sometimes light-sensitive eyespots at the anterior end.  Specialized flame cells help get rid of wastes.  The planarian is the most common free- living flatworm found in water or moist places.

19.  They are hermaphrodites producing both eggs and sperm, but they exchange sperm with each other during sexual reproduction.  Planarians also reproduce asexually by fragmentation.  Flukes and tapeworms often live in their host's digestive tract resistant to the host's enzymes.  They do not have a digestive system allowing the host to digest their food.

20.  Tapeworms are divided into sections called proglottids that each have a complete reproductive system producing fertilized eggs.  Tapeworms are hermaphroditic (one body having both sexual parts), and they fertilize their own eggs.  Ripe proglottids with their eggs pass out with the host's feces.

21.  Tapeworms anterior end is called the scolex and is modified with both hooks and suckers to attach to the host's intestines.  Humans most often get tapeworms from infected, undercooked pork, beef, or fish.  Tapeworm eggs can withstand boiling water so it is important to cook these meats well enough to destroy the eggs.

22.  Children sometimes get tapeworms by playing with the feces in the litter box of a cat, getting the eggs on their hands, and placing their hands or fingers in their mouth.  The longest tapeworm ever passed by a person was 39 meters.

23.  Flukes have complex life cycles that involve more than one host.  A fluke causes Schistosomiasis, a disease that affects 250 million people world wide.  This blood fluke attacks the kidneys, liver, and intestines causing progressive weakness.  It often takes 20 years to die from Schistosomiases, & there is no cure.

24.  The phylum Nematoda are the roundworms.  Roundworms are cylindrical in shape, tapered at both ends, and vary in length from being microscopic to 20 inches long.  Roundworms are pseudocoelomate [soo-doh- see-luh-meyt] having a body cavity that is not completely lined. Pinworm

25.  The body cavity or pseudocoel [soo-doh- seel] serves as a hydrostatic skeleton against which muscles can contract.  Unlike flatworms, roundworms have a complete gut.  This means that they have a one-way digestive tract with a gut that begins with a mouth and ends with an anus.  Therefore, they are usually able to digest food.

26.  Roundworms have no blood or heart.  Nutrients are distributed by a non-blood fluid which is not pumped.  Most roundworms are parasites and are found in all habitats.  They are bilaterally symmetrical and unsegmented. Hookworm

27.  Although they are cylindrical in shape, they usually taper at both ends.  They are covered with a thick protective cuticle that is flexible and can be molted.  They have separate sexes generally and reproduce sexually.

28.  The roundworm Trichinella, causes the disease called trichinosis.  People get trichinosis from eating infected, undercooked pork.  Trichinella gets into muscles and leaves calcium deposits which affect muscle contraction.  Trichinosis can affect the heart. Trichinella

29.  Another roundworm, Ascaris, parasitizes human lungs.  The Filaria worm attacks the lymphatic system causing great swelling.  Hookworms and pinworms are also roundworms which parasitize humans. Ascaris

30.  The phylum Rotifera includes microscopic worms found in aquatic and soil habitats.  They have a crown of cilia at their head end surrounding their mouth for movement and feeding.  Their bodies are covered with an external layer of chitin[kahy-tin].

31.  Having separate sexes, they reproduce sexually.  Some species contain only females and reproduce by parthenogenesis (unfertilized eggs developing into females).