Cnidarians Cnidarians actually exhibit radial symmetry in which similar body parts can be grouped around a central axis. Here we also observe a large jump on the evolutionary scale: tissues that perform specific functions.
Animals with radial symmetry look the same from all sides and have no head, front, or back. They do, however, have an oral surface, where the mouth is, and an aboral surface on the opposite side See figure 7.6 page 119
tissues Two layers present Epidermis covers body surface (external) Gastrodermis lines internal body cavity and is specialized for digestion There is also a narrow, gelatinous middle layer, mesoglea,that usually doesn’t contain cells. Forms “bell” of medusae
Two Tissue Layers 1. EPIDERMIS – OUTER LAYER 2. GASTRODERMIS – STOMACH CAVITY MESOGLEA – JELLY MATERIAL BETWEEN TISSUE LAYERS ABUNDANT IN JELLYFISH TO HELP THEM FLOAT
Cnidocytes Stinging cells Nematocyst capsules located on tentacles These are used for protection and feeding
Cnidocytes-Stinging Cells Within the cnidocyte is the nematocyst (which is like a capsule) The capsule has the stinging structure which is a hollow thread (Filament) with barbs Most contain a toxin Very small, but discharged in large numbers Usually the sting is only strong enough to kill zooplankton or tiny fish But there are exceptions!
Discharged nematocysts,Discharged nematocysts, stinging cells used for defense and prey capture, have been the plague of more than fish. stinging cells used for defense and prey capture, have been the plague of more than fish. Stings from certain jellyfish have resulted in death in a matter of hours, especially for infants.Stings from certain jellyfish have resulted in death in a matter of hours, especially for infants.
Digestive and nervous systems Digestive system is incomplete (sac-like with mouth only) Centrally located mouth surrounded by tentacles Tentacles capture and handle food Mouth opens into gut where food is digested
Nerve net throughout body coordinates movements Some jellyfish also have sensory cells and contractile cells
One Opening System Food enters through the mouth and is digested in the cells. Wastes are excreted through the mouth. WASTES, GAMETES OUT Sperm and eggs are released through the mouth. FOOD IN
Response No nervous system No brain Nerve net around mouth Nerves cover the body but do not tell the difference between body parts.
Respiration Via diffusion Body is two cell layers thick
Habitat Aquatic: Most are Marine A few are freshwater
Feeding 1. Carnivores (predators) 2. Process of feeding a. Tentacles sting prey with nematocysts b. Tentacles grab prey c. Prey pulled into mouth 3. Prey moved into gastro-vascular cavity (GVC)* 4. GVC makes enzymes, breaks down food, extra-cellular digestion 5. Undigested food moves back out of mouth Lion ’ s mane eats another jelly!
Process of feeding 3. Prey stuffed into gastro- vascular cavity (GVC)* 4. GVC makes enzymes, extra- cellular digestion 5. Undigested food back out mouth *incomplete digestive tract (no anus)
Locomotion A.Medusa- motile, free-swimming B.Polyps- sessile, attached to hard substrate Exceptions: 1. Hydra tumbles on tentacles 2. Sea anemones glide on pedal disc
Reproduction 1. Asexual budding 2. Sexual a. Medusae release sperm & eggs b. Larvae are free-swimming
Sexual reproduction Medusa is normally the sexual stage with epidermal gonads. Eggs and sperm released from medusa Zygote develops into swimming larva called a planula Planula settles on bottom to form colony Eventually, new medusa are formed
Life Cycle of a Typical Cnidarian Alternation of Generations One form is the polyp (a cylinder with the closed end attached to the substrate and the open end with the mouth and tentacles directed upward) The other form is the medusa, free- swimming, with the mouth underneath (like a jellyfish)
Life Cycle of a Typical Cnidarian Alternation of Generations Hermaphrodite sexual asexual
Cnidarian life cycle http://www.youtube.com/watch?v=ct9Ky Lmnu0Ihttp://www.youtube.com/watch?v=ct9Ky Lmnu0I http://www.youtube.com/watch?v=K9cF bJ8qYWghttp://www.youtube.com/watch?v=K9cF bJ8qYWg
Phylum Cnidaria The Classes of Cnidaria are: Anthozoa- Sea Anemones and Corals Hydrozoa- Hydra Scyphozoa- “true” jellyfish Cubozoa- “box-shaped” jellyfish Ctenophora- non stinging Cnidarians: Comb Jellies (covering separately)
Class Anthozoa All marine “flower animal” Corals, anemones, sea fans/whips, sea pansy Colonial polyps that normally lack a medusa stage Sting organisms around them Can move by crawling along the substrate Corals secrete calcium carbonate “shells” Most coral species possess symbiotic algae within body tissues called zooxanthellae
Anemone Video http://www.youtube.com/watch?v=NFO 4DwEkkr0http://www.youtube.com/watch?v=NFO 4DwEkkr0
Homework Research the relationship between clown fish and anemones http://video.nationalgeographic.com/vid eo/animals/invertebrates-animals/other- invertebrates/clownfish_amonganemon es/http://video.nationalgeographic.com/vid eo/animals/invertebrates-animals/other- invertebrates/clownfish_amonganemon es/
Class Scyphozoa True jellyfish. All marine Free swimming large medusa forms with polyp only in reproductive life They move by rhythmic contractions of the bell, but cannot fight against prevailing water currents Many with powerful stings
National geographic jellyfish Dance of the jellyfish http://video.nationalgeographic.com/vid eo/animals/invertebrates-animals/other- invertebrates/dance-jellyfish-eorg/http://video.nationalgeographic.com/vid eo/animals/invertebrates-animals/other- invertebrates/dance-jellyfish-eorg/ 1 minute
National geographic http://video.nationalgeographic.com/vid eo/animals/invertebrates-animals/other- invertebrates/jellyfish/http://video.nationalgeographic.com/vid eo/animals/invertebrates-animals/other- invertebrates/jellyfish/
Super Jellies http://www.youtube.com/watch?v=NbpB 5F9CcLchttp://www.youtube.com/watch?v=NbpB 5F9CcLc 3:31
Largest known jellyfish Lion’s Mane Jelly bell of a lion's mane jellyfish can be over 8 feet across tentacles can reach over 100 feet, and they have many of them - the lion's mane jellyfish has eight groups of tentacles, and there are 70-150 tentacles in each group
Encountering a lion's mane jellyfish probably won't be lethal, but it won't be fun, either. A lion's mane jellyfish sting usually results in pain and redness in the area of the sting. The sticky tentacles of a lion's mane jellyfish can sting even when the jellyfish is dead, so give lion's mane jellyfish on the beach a wide berth. In 2010, a lion's mane jellyfish washed ashore in Rye, NH, where it stung 50-100 unsuspecting batherswashed ashore
Class Hydrozoa Mostly polyp forms with reproductive medusa Freshwater and marine Physalia Portuguese man of war hydra
National geographic portuguese man of war http://animals.nationalgeographic.com/a nimals/invertebrates/portuguese-man- of-war/http://animals.nationalgeographic.com/a nimals/invertebrates/portuguese-man- of-war/
National geographic port. Man of war http://www.youtube.com/watch?v=RBd CpcapB0shttp://www.youtube.com/watch?v=RBd CpcapB0s
Ecological Role A.Predators and prey B.Neurotoxins in medical research C.Coral – jewelry, building, reefs (surfing!) D.Coral reefs - habitat for many different species, great biodiversity, protect coastline E. Symbiosis with other organisms