Cnidaria
A cnidarian neither needs nor possesses a respiratory system. The function of a respiratory system is to transport oxygen to an animal’s body cells in order to support cellular respiration, and to transport the poisonous CO2 produced as a waste product of cellular respiration out of the animal’s body. The reason that a cnidarian doesn’t need a respiratory system is because every cell in its body is in direct contact with the surrounding water. This means that oxygen can diffuse directly from the water and into a cnidarian’s body cells. Similarly, the CO2 produced in the animal’s cells is easily disposed of, because it diffuses directly into the surrounding water and is then carried away by currents.
Anthozoa
Like those of other cnidarians, the individual polyps have a cylindrical body crowned by a ring of tentacles surrounding the mouth. The mouth leads into a tubular pharynx which descends for some distance into the body before opening into the gastrovascular cavity that fills the interior of the body and tentacles. Unlike other cnidarians, however, the cavity is subdivided by a number of radiating partitions, or mesenteries. The gonads are also located within the cavity walls.
All cnidarian species can feed by catching prey with nematocysts; sea anemones are capable of catching fish and corals of catching plankton. Some of the species also harbour a type of algae, dinoflagellates called zooxanthellae, in a symbiotic relationship; the reef building corals known as hermatypic corals rely on this symbiotic relationship particularly. The zooxanthellae benefit by using nitrogenous waste and carbon dioxide produced by the host or, and the cnidarian gains photosynthetic capability and increased calcium carbonate production in hermatypic corals.
Anemones and certain species of coral live in isolation; however, most corals form colonies of genetically identical polyps. These closely resemble anemones in structure, although they are, generally, considerably smaller. stony coral are found in most seas
All cnidarian species can feed by catching prey with nematocysts; sea anemones are capable of catching fish and corals of catching plankton. Some of the species also harbour a type of algae, dinoflagellates called zooxanthellae, in a symbiotic relationship; the reef building corals known as hermatypic corals rely on this symbiotic relationship particularly. The zooxanthellae benefit by using nitrogenous waste and carbon dioxide produced by the host or, and the cnidarian gains photosynthetic capability and increased calcium carbonate production in hermatypic corals.
Anemones and certain species of coral live in isolation; however, most corals form colonies of genetically identical polyps. These closely resemble anemones in structure, although they are, generally, considerably smaller. stony coral are found in most seas
Scyphozoa
Scyphozoans usually display a four-part symmetry and have an internal gelatinous material called mesoglea, which provides the same structural integrity as a skeleton. The mesoglea includes mobile amoeboid cells originating from the epidermis. Scyphozoans have no durable hard parts, including no head, no skeleton and no specialized organs for respiration or excretion. Marine jellyfish can consist of as much as 98% water and therefore are rarely found in fossil form.
Unlike the hydrozoan jellyfish, hydromedusae, scyphomedusae lack a velum, which is a circular membrane beneath the umbrella that helps propels the (usually smaller) hydromedusae through the water. However, a ring of muscle fibres is present within the mesoglea around the rim of the dome, and the jellyfish swims by alternately contracting and relaxing these muscles.[6] The periodic contracting and relaxing propels the jellyfish through the water, allowing it to escape predation or catch its prey
Unlike the hydrozoan jellyfish, hydromedusae, scyphomedusae lack a velum, which is a circular membrane beneath the umbrella that helps propels the (usually smaller) hydromedusae through the water. However, a ring of muscle fibres is present within the mesoglea around the rim of the dome, and the jellyfish swims by alternately contracting and relaxing these muscles.[6] The periodic contracting and relaxing propels the jellyfish through the water, allowing it to escape predation or catch its prey
Hydrozoa
Hydrozoa (hydrozoans) are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most living in saltwater. The colonies of the colonial species can be large, and in some cases the specialized individual animals cannot survive outside the colony. A few genera within this class live in freshwater. Hydrozoans are related to jellyfish and corals and belong to the phylum Cnidaria.
Some examples of hydrozoans are the Freshwater Jelly (Craspedacusta sowerbyi), the freshwater polyps (Hydra),Obelia, the Portuguese Man o' War (Physalia physalis), the chondrophores (Porpitidae), "air fern" (Sertularia argenta), and the pink-hearted hydroids (Tubularia).
Some examples of hydrozoans are the Freshwater Jelly (Craspedacusta sowerbyi), the freshwater polyps (Hydra),Obelia, the Portuguese Man o' War (Physalia physalis), the chondrophores (Porpitidae), "air fern" (Sertularia argenta), and the pink-hearted hydroids (Tubularia).