What is a Cnidarian?
Definition: any invertebrate animal, as a hydra, jellyfish, sea anemone, or coral, considered as belonging to the phylum Cnidaria, characterized by the specialized stinging structures in the tentacles surrounding the mouth; a coelenterate
Definition: any invertebrate animal, as a hydra, jellyfish, sea anemone, or coral, considered as belonging to the phylum Cnidaria, characterized by the specialized stinging structures in the tentacles surrounding the mouth; a coelenterate
Body Plan:
Cnidarians are radially symmetrical. They have a central mouth surrounded by numerous tentacles that extend outward from the body. Cnidarians typically have a life cycle that includes two different-looking stages: a polyp and a medusa. A polyp is a cylindrical body with armlike tentacles and they are usually sessile. The mouth point upward. A medusa has a motile, bell-shaped body with the mouth on the bottom. Feeding: They paralyze their prey then pull it through its mouth and into its gastrovascular cavity. The digestion is extracellular and is completed intracellularly. Respiration, Excretion & Circulation: Following digestion, nutrients are usually transported throughout the body by diffusion. Cnidarians respire and eliminate the wastes of cellular metabolism by diffusion through their body walls. |
Response:
Cnidarians gather information from their environment using specialized sensory cells. Both polyps and medusas have a nerve net. Cnidarians also have statocysts and ocelli. Movement: Different cnidarians move in different way. For example, the hydrostatic skeleton consists of a layer of circular muscles and a layer of longitudinal muscles that enable them to move. Reproduction: They produce both sexually and asexually. Polyps can reproduce asexually by budding. In most cnidarians, sexual reproduction takes place with external fertilization in water. |