Phylum Cnidaria

Cnidarians - jellyfish, coral, hydra, sea anemone *Named after the stinging cells found on their tentacles called CNIDOCYTES

Cnidarians Are soft bodied, carnivorous animals that have stinging tentacles arranged in circles around their mouths. The simplest animals to have body symmetry and specialized tissues.

General Characteristics About 9000 species Simple nervous system Diploblastic organization Endoderm Ectoderm

Most Cnidarians have radial symmetry

General Characteristics Cont’d- Either tubular/vase or bell/cup shaped Only animal with cnidocytes Cnidocytes-specialized stinging cells (on tentacle) All marine (aquatic)

Cnidarians have two body forms: polyp (vase shaped)               medusa (cup shaped)

Body Plan Cnidarians’ bodies are organized around the gastrovascular cavity, where digestion takes place GV has a single opening that serves as both mouth and anus

Body Plan Cnidarians typically have a life cycle that includes two different looking stages: a polyp and a medusa. Polyp: a cylindrical body with arm like tentacles Medusa: a motile, bell-shaped body with the mouth on the bottom.

2 Layers of Cells Diploblastic: Gastrodermis: lines GV cavity Epidermis: lines the outside of the body (the skin)

Cnidarian Body Wall

Stinging Cells Have Cnidocytes Contain nematocysts: barbed thread-like structures inside the cnidocyte that shoots out and can puncture and inject a toxin or entangle prey

Cnidocyte

Feeding Gastrovascular cavity- a digestive chamber with one opening Inner gastrodermis secretes digestive juices into gastrovascular cavity which digests food and circulates nutrients

Feeding Cont.

Nervous and Movement sensory receptors Both polyp and medusa have a nerve net A loosely organized network of nerve cells that together allow cnidarians to detect stimuli Muscles help in directional movement & capturing prey

Polyp Medusa Life Cycles Cnidarians have two body forms that are representative of the sexual and asexual life cycles that they undergo. Polyp Medusa

Polyp Usually attaches to a substrate at the aboral end Oral end is surrounded by feeding tentacles

Medusa Sexual Shaped like an upside-down bowl Tentacles surround the mouth that is housed underneath the bell

Respiration, Excretion and circulation Following digestion, nutrients are usually transported throughout the body by diffusion. They respire and eliminate the wastes of cellular metabolism by diffusion through their body cells.

Reproduction Both sexual and asexual Sexual Gametes released into water Fertilization takes place to create free-swimming planula Asexual By budding

Generalized Cnidarian Life Cycle

Examples Scyphozoa: Jellyfish Anthozoa: Sea anemones & Corals Hydrozoa: Hydra Cubozoa: Box Jellies

Class Hydrozoa Ex. Hydras

The Hydra is a freshwater cnidarian What kind of symmetry does hydra have? Is it a medusa or a polyp?

Video of hydra at http://www. microscopyu

Includes hydras, fire corals, and Portuguese Man of War Display alternation of generations Polyp Medusa

Portuguese Man of War - cnidarian that floats in the water and has long tentacles

Class Scyphozoa True Jellyfish Small polyp stage during life cycle

Class Anthozoa Polyps that are flower-like Includes sea anemones, corals, sea whips, and sea fans

Coral Reefs are made from the skeletons of cnidarians

Coral Characteristics One of the most biologically diverse places in the world!

Coral characteristics Types of Corals: Hermatypic – reef forming corals, have zooxanthallae, found in warm, shallow waters

Coral Characteristics Zooxanthallae (type of Protist) form a symbiotic relationship with coral Zooxanthallae gives coral its color Coral polyps provide shelter Zooxanthallae

Coral Characteristics Two main types of corals (con’t) Ahermatypic – non-reef forming, grow in deep water, are found in polar to tropical waters

Coral Characteristics Coral reproduction Most are monoecious (hermaphroditic) External fertilization- release sperm and eggs into the water Many reproduce by budding as well (forms coral reefs)

Reef Structure Anatomy of a coral polyp

Reef Problems Disease Warming water temps – may be the cause of coral “bleaching” Increasing sediments Human footprints

Multimedia Sponge Images and Videos - http://www.junglewalk.com/video/Sponge-movie.htm  Cnidarian Images and Videos - http://www.junglewalk.com/video/Coelantrate-movie.htm General Invertebrate Movies at National Geographic  --- really good video on the portuguese man of war (under invertebrates)   Hydra Video at  http://www.schooltube.com/video/55045/Hydra