09/12/2012. Classification. Characteristics. Learning Outcome G2. Student Achievement Indicators. Phylum Porifera The Sponges

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1 Learning Outcome G2 Analyse the increasing complexity of the Phylum Porifera and the Phylum Cnidaria Learning Outcome G2 Phylum Porifera & Phylum Cnidaria Student Achievement Indicators Students who have fully met this learning outcome will be able to: Examine members of the Phylum Porifera and identify their unifying characteristics Describe how poriferans carry out their life functions Examine members of the Phylum Cnidaria and identify their unifying characteristics Describe how cnidarians carry out their life functions Compare polyp and medusa with respect to structure, general function, and motility Suggest the advantages of a motile form in the life cycle of a cnidarian Explain the evolutionary significance of colonial (poriferan) versus multicellular (cnidarian) life forms Describe the ecological roles of sponges and cnidarians Phylum Porifera The Sponges Kingdom Animalia Phylum Porifera Classification An invertebrate Characteristics Sessile (do not move) Found in oceans and lakes Have specialized cells but these cells are not arranged into organs or tissues No nervous system or brain No muscle tissue, which means sponges are not capable of any type of movement 1

2 Characteristics Highly successful group; 500 million years old An evolutionary dead end, because no other groups have developed from the sponges Spicules make up the internal skeleton of the sponges Amebocytes are specialized cells that build spicules from calcium carbonate (CaCO 3 ) or silicon dioxide (SiO 2 ). No body symmetry Filter feeder Feeding Collar cells with flagellum create water currents that brings water into and out of the cells Water and food enter the sponge through small pores and exit via the osculum Digestion occurs in the collar cells or amebocytes that wander around the middle layer of the sponge 2

3 Sexual Generally hermaphroditic (produce both male and female gametes) Have a motile larvae stage An egg (n) is fertilized by a sperm (n) and develops into a free-swimming larvae (2n). Larve attaches to bottom undergoes metamorphosis After metamorphosis an adults sponge develops (2n) Asexual Budding or branching Produces gemmules under unfavorable conditions Gemmules are sphere-shaped collections of amebocytes surrounded by a tough layer of spicules. These gemmules can survive long periods of freezing temperatures and droughts, which would kill an adult sponge. When conditions become favorable again these gemmules will develop into a new adult sponge. Ecological Roles Shelter for invertebrates Preyed on by bacteria, algae and other microscopic organisms Form symbiotic relationships with photosynthetic organisms. In this relationship the photosynthetic organisms provide food and oxygen. The role of the sponge is to remove waste Specialized amebocytes called boring sponges are vital in marine habitats because they clear the ocean floor Protection Produce toxins and antibiotics that are used to deter bacteria and algal predators 3

4 Human Uses Phylum Cnidaria Caribbean sponge has a compound that may be useful in fighting leukemia and herpes Classification Class Cubozoa Kingdom Animalia Phylum Cnidaria Class: Cubozoa (sea wasps or box jellyfish) Class: Scyphozoa (jellyfishes) Class: Anthozoa (anemones and corals) Class: Hydrozoa (hydra) Class Scyphozoa Class Anthozoa 4

5 Class Hydrozoa Characteristics Invertebrate Radial symmetry Have true tissue, which allows specialization Only have two germ layers: ectoderm and endoderm Middle layer is not a mesoderm, but a layer composed of a jelly-like substance called mesoglea. This group includes jellyfish, hydra, sea anemone and reef coral Aquatic organisms Generally marine, but there are fresh water species such as hydra A nerve net encircles the body Some free swimming species have a ring of nerve cells around the bell (perhaps a primitive beginning of a central nervous system) Have coordination of nerves and muscles Hydra Feeding Capture food using specialized cells within the tentacles called cnidocysts, which contains small sacs called nematocysts. Nematocysts contain coiled, hollow tubes that shoot out rapidly and penetrates the skin of the prey These nematocysts may contain toxins that paralyze the prey Capture food and digest it in a sac-like cavity that has a single opening Waste is expelled from the same opening This opening is controlled by muscle, which allows cnidarians to engulf larger prey 5

6 Alternation of generations lifecycle Two body forms: polyp and medusa 1. Polyp Has a sessile tube-like body within the oral end directed upwards Vental end is attached to the ocean/lake floor Example hydra 2. Medusa Bell-shaped organism Mouth is located on the underside Have a thick middle layer called the mesoglea Cnidarians are often known as jellyfish due to their medusa state, although some species only have a polyp stage Sexual Egg/sperm arise from gastrodermal cells that have migrated to specific locations in the epidermis of the polyp or on the underside of the medusa Egg/sperm are released into the water and undergo external fertilization Zygote develops into a free-swimming ciliated larva called a planula Planula has an elongated body shape, is radially symmetrically, and has no gastrovascular cavity or mouth Sexual Planula attaches to substrate and develops into a hydroid colony (polyp stage) Some hydroid colonies do not produce a free swimming medusa stage Example hydra Hydroid colonies exhibit specialization These colonies are used to facilitate feeding and reproduction These colonies are also used as a defense mechanisms. 6

7 in Hydra Hydra may reproduce asexually Budding outgrowth of body walls Regeneration similar to sponges Hydra also reproduce sexually during unfavorable conditions May be hermaphroditic or have separate sexes After fertilization zygote divides and becomes an embryo that is enclosed in a protective case. This encased embryo is called a cyst, and it drops of the parent and lies dormant until favorable conditions usually to spring. Protection Used the same mechanisms as in feeding Specialized cells within the tentacle called cnidocytes that can expel a poison that can be used to deter predators. Ecological Roles Involved in symbiotic relationships with many organisms Example - sea anemone and fish, shrimp and small animals. These small organisms live among the tentacles of the very large sea anemone. The sea anemone protects the symbiont and provides food. In return the sea anemone is cleaned and protected by these symbionts from potential predators. Also Provide habitats for many small invertebrates and microorganisms Example - coral reefs Human Uses Protect coasts areas from damage caused by storms and large waves. These reefs are being damaged by pollution Once damaged the calcium carbonate skeleton of these reefs break apart and no longer offer protection to our coastal areas Coral is used to make beautiful jewelry and decorative articles Corals produce certain chemical for their defense Some of these chemicals can be used to manufacture drugs against cancer, and some toxins produced by corals are used by scientists to study and understand the function of nerve cells. 7