The Phylum Cnidaria
A Brief Overview
Cnidaria or Coelenterata is a phylum containing over 10,000 species of animals found exclusively in aquatic and mostly marine (saltwater) environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium (animal tissue) that are mostly one cell thick. They have two basic body forms swimming medusa (jellyfish) and sessile (immobile) polyps (cylindrical in shape and elongated at the axis of the vase-shaped ), both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes. Both forms have a single orifice (opening) and body cavity that are used for digestion and respiration. Many cnidarian species produce colonies that are single organisms composed of medusa-like or polyp-like zooids, or both. Cnidarians' activities are coordinated by a decentralized nerve net and simple receptors. Several free-swimming Cubozoa (box jellyfish) and Scyphozoa ("true" jellyfish) possess balance-sensing statocysts (receptor), and some have simple eyes. Not all cnidarians reproduce sexually; many have complex lifecycles. Cnidarians are classified into four main groups: the almost wholly sessile Anthozoa (sea anemones, corals, sea pens); swimming Scyphozoa(jellyfish); Cubozoa (box jellies); and Hydrozoa, a diverse group that includes all the freshwater cnidarians as well as many marine forms, and has both sessile members such as Hydra and colonial swimmers such as the Portuguese Man o' War (blue bottle jellyfish). The organisms found in this phylum do not contain circulatory organs. Instead of a circulatory system, Cnidarians have a Gastro vascular cavity, which functions in both digestion and the distribution of nutrients and particles to all parts of the body. The radially symmetrical cnidarians have a sac-like body in two distinct layers, the epidermis and gastrodermis (layers of epithelial tissue), with a jellylike layer called the mesoglea in between. Extracellular digestion takes place within the central cavity of the sac-like body. This cavity has only one opening to the outside and, in most cnidarians, that is surrounded by tentacles which serve to capture prey. Example: Digestion in hydra occurs in gastrovascular cavity.
Cnidaria or Coelenterata is a phylum containing over 10,000 species of animals found exclusively in aquatic and mostly marine (saltwater) environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium (animal tissue) that are mostly one cell thick. They have two basic body forms swimming medusa (jellyfish) and sessile (immobile) polyps (cylindrical in shape and elongated at the axis of the vase-shaped ), both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes. Both forms have a single orifice (opening) and body cavity that are used for digestion and respiration. Many cnidarian species produce colonies that are single organisms composed of medusa-like or polyp-like zooids, or both. Cnidarians' activities are coordinated by a decentralized nerve net and simple receptors. Several free-swimming Cubozoa (box jellyfish) and Scyphozoa ("true" jellyfish) possess balance-sensing statocysts (receptor), and some have simple eyes. Not all cnidarians reproduce sexually; many have complex lifecycles. Cnidarians are classified into four main groups: the almost wholly sessile Anthozoa (sea anemones, corals, sea pens); swimming Scyphozoa(jellyfish); Cubozoa (box jellies); and Hydrozoa, a diverse group that includes all the freshwater cnidarians as well as many marine forms, and has both sessile members such as Hydra and colonial swimmers such as the Portuguese Man o' War (blue bottle jellyfish). The organisms found in this phylum do not contain circulatory organs. Instead of a circulatory system, Cnidarians have a Gastro vascular cavity, which functions in both digestion and the distribution of nutrients and particles to all parts of the body. The radially symmetrical cnidarians have a sac-like body in two distinct layers, the epidermis and gastrodermis (layers of epithelial tissue), with a jellylike layer called the mesoglea in between. Extracellular digestion takes place within the central cavity of the sac-like body. This cavity has only one opening to the outside and, in most cnidarians, that is surrounded by tentacles which serve to capture prey. Example: Digestion in hydra occurs in gastrovascular cavity.
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Dendrogyra cylindricus (Pillar Coral)
Pillar coral (Dendrogyra cylindricus) is a hard coral found in the western Atlantic Ocean and the Caribbean Sea. It is a digitate coral -that is, it resembles fingers or a cluster of cigars, growing up from the sea floor without any secondary branching. It is large and can grow on both flat and sloping surfaces at depths down to 20 m (65 feet). It is one of the few types of hard coral in which the polyps can commonly be seen feeding during the day. Pillar coral is a zooxanthellate (animals symbiotic with algae)species, with symbiotic dinoflagellate algae living within the tissues. In sunlight these undergo photosynthesis and most of the organic compounds they produce are transferred to their host, while they make use of the coral's nitrogenous wastes. These algae give the coral its brownish color and restrict it to living in shallow water into which the sunlight can penetrate. This organism does not contain any circulatory organs, but they have a Gastro vascular cavity, which functions in both digestion and the distribution of nutrients and particles to all parts of the body.
Pillar coral (Dendrogyra cylindricus) is a hard coral found in the western Atlantic Ocean and the Caribbean Sea. It is a digitate coral -that is, it resembles fingers or a cluster of cigars, growing up from the sea floor without any secondary branching. It is large and can grow on both flat and sloping surfaces at depths down to 20 m (65 feet). It is one of the few types of hard coral in which the polyps can commonly be seen feeding during the day. Pillar coral is a zooxanthellate (animals symbiotic with algae)species, with symbiotic dinoflagellate algae living within the tissues. In sunlight these undergo photosynthesis and most of the organic compounds they produce are transferred to their host, while they make use of the coral's nitrogenous wastes. These algae give the coral its brownish color and restrict it to living in shallow water into which the sunlight can penetrate. This organism does not contain any circulatory organs, but they have a Gastro vascular cavity, which functions in both digestion and the distribution of nutrients and particles to all parts of the body.
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Physalia physalis (Bluebottle)
The Portuguese man o' war (Physalia physalis), also known as the Portuguese man-of-war, Man-Of-War, or bluebottle, is a jellyfish-like marine cnidarian of the family Physaliidae. Its venomous tentacles can deliver a powerful sting. Despite its outward appearance, the man o' war is not a jellyfish but a siphonophore, which
differs from jellyfish in that it is not actually a single organism, but a colonial organism made up of many minute individuals called zooids. Each of these zooids is highly specialized, and, although structurally similar to other solitary animals, they are attached to one another and physiologically integrated to the extent that they are incapable of independent survival. This organism does not contain any circulatory organs, but they can easily absorb oxygen when needed through their thin bodies. They also have a Gastro vascular cavity, which functions in both digestion and the distribution of nutrients and particles to all parts of the body.
The Portuguese man o' war (Physalia physalis), also known as the Portuguese man-of-war, Man-Of-War, or bluebottle, is a jellyfish-like marine cnidarian of the family Physaliidae. Its venomous tentacles can deliver a powerful sting. Despite its outward appearance, the man o' war is not a jellyfish but a siphonophore, which
differs from jellyfish in that it is not actually a single organism, but a colonial organism made up of many minute individuals called zooids. Each of these zooids is highly specialized, and, although structurally similar to other solitary animals, they are attached to one another and physiologically integrated to the extent that they are incapable of independent survival. This organism does not contain any circulatory organs, but they can easily absorb oxygen when needed through their thin bodies. They also have a Gastro vascular cavity, which functions in both digestion and the distribution of nutrients and particles to all parts of the body.
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Olindias formosa (Flower Hat Jelly)
The Flower Hat Jelly (Olindias formosa) is a species of jellyfish occurring in the West Pacific off southern Japan. Characterized by lustrous tentacles that coil and adhere to its rim when not in use, the flower hat jelly's bell is translucent and pinstriped with opaque bands, making it easily recognizable. The Flower Hat Jelly Fish is one of the 14 prettiest jellies in the world. The flower hat jelly can grow to be about 15 cm (6 inches) in diameter. Flower hat jelly fish live short lives, approximately 4–6 months. Its diet consists mostly of small fish. Similar to other jellies, they grow or shrink based on the availability of food. When the food Supply is short; they shrink so they need less and grow again when food is abundant. They use their tentacles to catch small fish. Flower Hat jelly fish will eat each other. Its sting is painful but is not deadly to humans. It is powerful enough to leave a rash. This organism does not contain any circulatory organs, but they can easily absorb oxygen when needed through their thin bodies. They also have a Gastro vascular cavity, which functions in both digestion and the distribution of nutrients and particles to all parts of the body.
The Flower Hat Jelly (Olindias formosa) is a species of jellyfish occurring in the West Pacific off southern Japan. Characterized by lustrous tentacles that coil and adhere to its rim when not in use, the flower hat jelly's bell is translucent and pinstriped with opaque bands, making it easily recognizable. The Flower Hat Jelly Fish is one of the 14 prettiest jellies in the world. The flower hat jelly can grow to be about 15 cm (6 inches) in diameter. Flower hat jelly fish live short lives, approximately 4–6 months. Its diet consists mostly of small fish. Similar to other jellies, they grow or shrink based on the availability of food. When the food Supply is short; they shrink so they need less and grow again when food is abundant. They use their tentacles to catch small fish. Flower Hat jelly fish will eat each other. Its sting is painful but is not deadly to humans. It is powerful enough to leave a rash. This organism does not contain any circulatory organs, but they can easily absorb oxygen when needed through their thin bodies. They also have a Gastro vascular cavity, which functions in both digestion and the distribution of nutrients and particles to all parts of the body.