Cnidaria
*Basic Characteristics
Basic characteristics:
1. Radial (primary) or biradial symmetry
2. Gastrovascular cavity for digestion
3. Tentacles- feeding, locomotion, defense
4. Cnidocytes- stinging cells (nematocysts)
5. 2 Body Forms-
a. Polyp: Cylindical, attached mouth and tentacles upright
b. Medusa- umbrella, mouth, and tentacles
c. Polymorphic or alternates between polyp and medusa
1. Radial (primary) or biradial symmetry
2. Gastrovascular cavity for digestion
3. Tentacles- feeding, locomotion, defense
4. Cnidocytes- stinging cells (nematocysts)
5. 2 Body Forms-
a. Polyp: Cylindical, attached mouth and tentacles upright
b. Medusa- umbrella, mouth, and tentacles
c. Polymorphic or alternates between polyp and medusa
*Cnidocytes
-Cnidocytes have organelles that are called cnidae and there are about thirty types of cnidae that can be sticky, serve as an anchor to the cnidarian, or that is toxic.
-The most common type of cnida is nematocysts. They have intercellular cellular capsules containing a tube used to inject toxins.
-Cnidocytes are used in prey capture and defense.
-The most common type of cnida is nematocysts. They have intercellular cellular capsules containing a tube used to inject toxins.
-Cnidocytes are used in prey capture and defense.
*Life Cycle
-Most cnidarians have a polyp stage (tentacles facing up) and a medusa stage (tentacles facing down).
-Polyps are typically attached to a surface (sessile).
-Polyps produce other polyps and medusae asexually through budding.
-Medusae are motile and has tentacles pointing downward ("true jellyfish").
-Medusae are dioecious and reproduce sexually.
-Fertilization occurs externally and panula (free swimming larvae) results from this fertilization.
-The gastrovascular cavity also functions as a hydrostatic skeleton (use of body cavity fluids to give support).
-Polyps are typically attached to a surface (sessile).
-Polyps produce other polyps and medusae asexually through budding.
-Medusae are motile and has tentacles pointing downward ("true jellyfish").
-Medusae are dioecious and reproduce sexually.
-Fertilization occurs externally and panula (free swimming larvae) results from this fertilization.
-The gastrovascular cavity also functions as a hydrostatic skeleton (use of body cavity fluids to give support).