Cnidaria

Cnidaria is a phylum and it contains over 10,000 different species. 1. Feeding- Cnidaria are filter feeders.Cnidarians feed in several ways, predation, absorbing dissolved organic chemicals, filtering food particles out of the water, and obtaining nutrients from symbiotic algae within their cells. 2. Respiration- There are no respiratory organs, and both cell layers absorb oxygen from and expel carbon dioxide into the surrounding water. 3. Circulation When the water in the digestive cavity becomes stale it must be replaced, and nutrients that have not been absorbed will be expelled with it. 4. Excretion- Once the food is in the digestive cavity, gland cells in the gastroderm release enzymes that reduce the prey to slurry, usually within a few hours. 5. Response- Cnidaria have no brains or even central nervous systems. Instead they have decentralized nerve nets consisting of sensory neurons that generate signals in response to various types of stimulus, such as odors, motor neurons that tell muscles to contract, and "cobwebs" of intermediate neurons to connect them. 6. Movement- In medusae the only supporting structure is the mesoglea. These animals have no head either. 7. Reproduction- In the Cnidaria sexual reproduction often involves a complex life cycle with both polyp and medusa stages. All known cnidaria can reproduce asexually by various means, in addition to regenerating after being fragmented.