Cnidarians Part Deux HW:

Reproduction  Most cnidarians have two forms:  Polyp – tube shaped body with a mouth surrounded by tentacles  Medusa – umbrella shaped body and tentacles that hang down. The mouth is on the ventral side between the tentacles.

Reproduction  The two forms of cnidarians can be seen in the life cycle of a jellyfish:  The dominant form varies depending on the type of cnidarian.

Jellyfish Reproduction  To reproduce jellyfish (in the medusa stage) release egg and sperm into the water.  When the two meet fertilization occurs – in the water not internally.  Resulting zygotes (product of fertilization) will develop into free-swimming larvae that will grow into polyps.

Jellyfish Reproduction  Jellyfish polyps reproduce asexually to form new medusae (plural of medusa).  So jellyfish alternate generationally from the polyp stage and the medusa stage.  What does this mean???

Cnidarian Diversity  You know that jellyfish and sea anemone’s are cnidarians, but what else is there?  Hydroids  Jellyfishes  Sea Anemone & Coral  How do these three groups consititute 10,000 species????

Hydroids  Hydroids:  ~ 2700 species  Have both polyp and medusa stages in their life cycles.  Most form colonies (like the Portugese Man of War).  Another example of hydroids is the hydra – which we will study.

Jellyfishes  Jellyfishes:  ~200 species  Transparent/transulscent appearance  Medusa is the dominant form, but there is a polyp stage  One well known example is the box jellyfish.  Box jellyfish get their name because the medusa form has a boxlike structure.  A sting from a box jellyfish can kill a human.

Sea Anemones & Corals  ~ 6200 species (WOW)  Polyp stage is the dominant stage.  Recent research suggests bilateral symmetry for the polyps, unlike jellyfish and hydroids.

Sea Anemones & Coral  Sea anemones live as individuals and coral lives in colonies.  Coral secretes calcium carbonate to protect itself.  This creates a hard shell around their soft bodies.  As you may know coral reefs are endangered.  Their health depends on: proper water temperature, adequate light, and appropriate water depth.  Rises in water temperature & pollution pose a threat to this pretty cnidarian.

Summary  The notes from the past two days have described the body structure, digestive & nervous systems, reproduction, and diversity of cnidarians.  You need to read & study these notes in addition to completing the labs and color plates!!!!  REMINDER: DO NOT WRITE IN THE COLOR PLATE BOOKS!!!