Biology is life

PHYLUM CNIDARIA !!!

 

 

UNIQUE CHARACTERISTICS 

 

• In Greek means ‘stinging structures’                            
  
   
• Most marine, few fresh water species
•  e.g :Obelia sp.
•  Eumetazoans (has true tissues)
• Diploblastic 

    -2 well developed tissue layer

1.  Inner gastrodermis/ endoderm
2. Outer epidermis/ectoderm 

          *Gelatinous mesoglea between layers*

-Radial symmetry
-Acoelomate 
-Have reproductive,circulatory, and gastrovascular systems
-Possess both muscle and nerve cells

• Exhibit dimorphism / polymorphism (i.e. two types body plan)

     a) Sessile polyps
            -2 types of polyp

    
                  * Reproductive polyp

                                          
                  * Feeding polyp : equipped with tentacles
 

                b) Motile medusa

• Medusa : free swimming adult stage that reproduces sexually  

• Polyp : sessile larval stage that reproduces asexually; by budding

      

• Body plan of a polyp/medusa : it has single opening leading to gastrovascular cavity which function as mouth (site of digestion) and anus (waste discharge)

 

 

• -Surrounding the opening is a series of tentacles
• -Tentacles have specialized stinging cells called cnidocytes/cnidoblast/nematocytes/nematoblast  -Function : capture of prey and defense

 

Cnidocytes

 

 

                                            

3 Classes of Coelenterata : 

1. Class Hydrozoa (hydra, Obelia sp.) 

• live in fresh water
• polyps only
• cnidocytes in its tentacles
• reproduction: 

      - asexual - budding 

       - sexual – takes place during fall or when water is   stagnant. 

 

 

 2. Class Scyphozoa (jellyfish, Aurelia sp.)

 

3. Class Anthozoa (sea anemone, Actinia sp.)

 

Life cycle of Obelia sp.