Lesson Activity on Sponges, Cnidarians, Flatworms and Roundworms

1 Sponges – phylum Porifera Asymmetrical Invertebrates No tissues, organs or organ systems Over 5000 species in a variety of sizes, shapes and colors

Sponges Are Pore-Bearers Porifera = pore bearer Almost all live in shallow areas of the ocean Mainly sessile Sessile - it is permanently attached to a surface for all of its adult life Get food by filter feeding (filter small particles of food from the water as it passes by or through some part of the organism)

Cell Organization in Sponges Sponges have different types of cells that perform different functions Sponge embryos do not develop endoderm or mesoderm, so their cells are not organized into tissues Endodrem and Mesoderm: The germ layers in the process by which the embryo is formed and develops

Why Are Sponges Important? Can be separated into individual types of cells but if left alone (over time) the cells will reorganize back into a sponge Believed to have evolved from colonial, flagellated protists Demonstrate the major evolutionary step between unicellular life to a division of labor among groups of organized cells

Reproduction in Sponges Reproduce both sexually and asexually Asexually through fragmentation or external buds Buds may break off and float away to become new animals or they may remain attached and form a colony

Sexual Reproduction in Sponges All are hermaphrodites Hermaphrodites can produce both eggs and sperm AT different times It increases the likelihood of fertilization in sessile animals Cannot self-fertilize Can use either internal or external fertilization

Internal Fertilization Internal fertilization – sperm is brought into the body and fertilization takes place inside the organism Eggs remain inside the sponge Collar cells collect sperm and transfer it to the amoebocytes

External Fertilization External fertilization – sperm and eggs are released into the water and fertilization occurs out in the water Some sponges in temperate zones produce gemmules which are like seeds and lie dormant over the winter and grow into new sponges in the spring

2.Cnidarians (the C is silent)

What are Cnidarians? Marine invertebrates 9,000 species Include jellyfish, corals, sea anemones and hydras Found worldwide, but mainly in warmer oceans

Characteristics of Cnidarians Radial Symmetry 2 cell layers (the ectoderm and the endoderm) with one body opening Ectoderm becomes a protective outer layer of cells The endoderm is internal and is adapted mainly to aid in digestion

Cnidarians Body Forms 2 basic body forms that occur at different stages of their life cycle Polyp - Tube shaped body and a mouth surrounded by tentacles Dominant in hydras (spends most of its life in this form) Corals and sea anemones only have this stage Medusa- body shaped like an umbrella with tentacles hanging down Dominant in jellyfish

Body Systems Have simple nervous systems and other tissues Nerve net – conducts nerve impulses from all parts of the body There is no brain Both cell layers have cells that can contract like muscles Simple digestive system

Digestion in Cnidarians Predators that capture or poison their prey with nematocysts Nematocyst - capsule that contains a coiled, thread like tube that may contain a toxin Digestion involves enzymes and cells adapted for this purpose Digestion takes place in the gastrovascular cavity Undigested materials are ejected back out the mouth

Reproduction in Cnidarians Sexual reproduction usually occurs in the medusa stage (unless there is none) Asexual may occur in either the polyp or medusa stage Technically not alternation of generations like in plants because both stages are diploid

Common Reproductive Cycle in Cnidarians Male medusae release sperm Female medusae release eggs Fertilization occurs The zygotes develops into an embryo and then into a larva The free swimming larva settles down and develops into a polyp The polyp reproduces asexually to form male and female medusae

Respiration Oxygen enters cells directly Because of its body plan, no cell is ever far from water Oxygen dissolved in the water diffused directly into the cells Carbon dioxide and other wastes diffuse directly out and into the water

Diversity of Cnidarians Most of the 9000 species belong to one of 3 classes Hydrozoans Scyphozoans Anthozoans

Most Hydrozoans Form Colonies Class Hydrozoa has 2 groups – 1. hydroids (hydra) and 2. Siphonophores (Portuguese Man-O-War) Most hydroids are branching polyp colonies formed by budding Siphonophores are floating or swimming colonies of medusae Each individual in Siphonophores colonies has a different function, but they all function together for the survival of all

Scyphozoans are the Jellyfish Medusa stage is dominant Can be found everywhere in the oceans and as deep as1000 meters The gastrovascular cavity has 4 internal divisions Range in size from microscopic to more than a meter

Anthozoans Build Coral Reefs Found in tropical, temperate and arctic seas Cnidarians that exhibit only the polyp form Have many divisions in their gastrovascular cavity Corals live in colonies Sea Anemones live as individual animals

Coral Reefs Corals secrete a calcium carbonate ‘skeleton’ that remains after it dies forming reefs Reefs grow very slowly Coral reefs are very sensitive towards the changes in temperature and water level

Corals Most of Coral form mutual relationships with photosynthetic protists which offer the corals oxygen and food and use the carbon dioxide and wastes from the corals These protists are primarily responsible for the bright colors of coral reefs If these protists leave the corals, the corals die

Origins of Cnidarians and Sponges Sponges represent the oldest animal phylum dating from 700 million years ago Thought to have evolved directly from flagellated protists similar to the collar cells of today Cnidarians first appear about 630 million years ago. We have little evidence for cnidarians as they are soft bodied and do not fossilize well Believed that cnidarians evolved from protists

3. Flatworms – phylum Plathelminthes

What Is a Flatworm? Acoelomates - thin solid bodies Bilateral symmetry Approx. 14,500 species Live in salt and freshwater Planarians (Class Turbellaria) Tapeworms (Class Cestoda) Flukes(Class Trematoda)

Feeding and Digestion in Planarians Feed on dead or slow moving organisms Pharynx – tube-like muscular organ that a planarian extends from its mouth to feed Enzymes begin digesting the food outside the animal’s body Food is digested by individual cells Cells lining the digestive tract obtain food by phagocytosis

Nervous Control in Planarians Some have a nerve net, other have the beginnings of a central nervous system (CNS) CNS in planarians 2 eyespots 2 nerve cords that run the length of the body Brain-like structure called a ganglion which sends messages to/from the eyespots and along the nerve cords

Reproduction in Planarians Most are hermaphrodites During sexual reproduction individual flatworms exchange sperm Fertilization is internal Zygotes (fertilized eggs) are released into the water to hatch

Planarians Can Also Reproduce Asexually If it is damaged it can regenerate (grow back) new body parts Missing body parts are replaced through mitosis If cut in half the head end will grow a new tail and the tail end will grow a new head

Feeding and Digestion in Parasitic Flatworms Parasites are adapted to living inside a host and obtaining nutrients from their host Have mouthparts with hooks to hold the worm inside its host Did not evolve complex nervous or muscular systems because they didn’t need them

Tapeworms (Class Cestoda) Parasitic Made up of a head (scolex) and repeating sections (proglottids) The proglottids are detachable and each contains nerves, muscles, flame cells, as well as male and female reproductive organs Each proglottid can have up to100,000 eggs A tapeworm can have as many as 2,000 proglottids

Flukes(Class Trematoda) Flukes are parasitic flatworms that embed themselves in the internal organs of vertebrates Feeds on cells, blood and other fluid of the host Blood flukes can cause schistosomiasis

4. Roundworms phylum Nematoda

What is a Roundworm? Varied habitat - live in soil, saltwater and freshwater environments Most are parasitic Smaller than tapeworms with a thick outer covering that keeps them from being digested Tapered at both ends

Muscular and Digestive Systems of Roundworms Have a pseudocoelom 2 body openings (mouth and anus) Simplest animals with a tubelike digestive system Have pairs of lengthwise muscles Lack circular muscles Move in a thrashing motion

Diversity of Roundworms Free-living species have well developed eyespots/sensory organs Some species are parasitic to plants and fungi Can form symbiotic relationships with bacteria 50 species are human parasites (including hookworm and pinworm)

Roundworms infect humans by several methods Can go through the host’s: Digestive tract (Ascarsis) Through the skin (Hookworms) Through undercooked food (pigs infected with Trichinella)

Roundworm parasites of other organisms Nematodes infect pine trees, cereal crops and food plants Attracted to plant roots 1200 species cause disease in plants Soil nematodes invade roots for food