CLASS OF CNIDARIA


                                  CLASS OF HYDROZOA (HYDRA)
           

 

• Internal space for digestion is the gastrovascular cavity
• Gastrovascular cavity has one opening, the mouth
• Exoskeleton of chitin
• Are almost entirely marine and predators
• Sexual reproduction produces the planula larvae
• Two body forms, a polyp and medusea
• Presence of stinging cells called Cnidocytes
• 7 orders consisting of 2700 species
• Hydrozoans have many cell types, but form only two tissue types for their bodies, epidermus and gastrodermis. Their bodies can range in size from the planula larvae which is measured in micrometers to massive colonial corals covering imense amounts of area.
• Though these organisms feed on smaller organisms, their digestive system is a simple gastrovascular cacity lined with flagellated cells that circulate food in with the filtering of water.
• The use of Cnidocytes enable the Hydrozoans to paralyze prey as well as ward off predators. There stinging cells are jettosoned after use and interstitial cells regenerate new ones. Developing Cnidocytes are called Cnidoblasts.

             CLASS OF ANTHOZOA (SEA ANAEMONE)

• Tropical marine habitat.
• Mouth surrounded by tentacles with nematocysts.
• Partioned gastrovascular cavity.
• Secretes nonliving substance around outside of body to support and protect soft body tissues.
• Reproduces sexually by producing a free-swimming larva (planula) or asexually by budding or fission.
• Cylindrical, with radial symmetry.
• Anthozoans vary greatly in appearance. Many species are shades of red, pink and purple, while others are blue, yellow, white and orange. They range from less than half an inch to large colonial sea pens that can exceed two feet.
• Anthozoans live singly or in colonies.
• Anthozoans have special glands that secrete digestive fluids. Some have been known to digest extremely large fish.
• Anthozoans are found around reefs and shallow waters. Since they help build coral reefs they have been valuable to scientists in learning about the past climates of certain regions.

                               CLASS OF SCYPHOZOA

• Class Scyphozoa, an exclusively marine class of animals with about 200 known species, includes all the jellies. 
• The defining characteristic of this class is that the medusa is the prominent stage in the life cycle, although there is a polyp stage present . 
• Members of this species range from 2 to 40 cm in length, but the largest scyphozoan species, Cyanea capillata, can reach a size of 2 m across. 
• Scyphozoansdisplay a characteristicbell-like morphology
• In scyphozoans, nerve cells are scattered over the entire body
•  These animals possess a ring of muscles lining the dome of the body, which provides the contractile force required to swim through water.
•  Scyphozoans are dioecious animals, having separate sexes.
•  The gonads are formed from the gastrodermis with gametes expelled through the mouth. 
• Planula larvae are formed by external fertilization; they settle on a substratum in a polypoid form known as scyphistoma. 
• These forms may produce additional polyps by budding or may transform into the medusoid form. 
• The life cycle of these animals can be described as polymorphic because they exhibit both a medusal and polypoid body plan at some point .