why are cnidarians radially symmetrical?
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Body plan. The body plan of cnidarians is unique because these organisms show radial symmetry, making these animals very different from those that evolved before them. Radial symmetry means that they have a circular body plan, and any cut through the center of the animal leaves two equal halves.
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Both ctenophores and cnidarians have a type of muscle that, in more complex animals, arises from the middle cell layer, and as a result some recent text books classify ctenophores as triploblastic, while others still regard them as diploblastic.
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Basal animals are animals which have radial symmetry in their body plans. They have very simple bodies and tend to be diploblastic.
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Only sponges (phylum Porifera) have asymmetrical body plans. Some animals start life with one type of body symmetry, but develop a different type as adults; for example, sea stars are classified as bilaterally symmetrical even though their adult forms are radially symmetrical.
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Cnidarians contain specialized cells known as cnidocytes (“stinging cells”), which contain organelles called nematocysts (stingers). These cells are present around the mouth and tentacles, serving to immobilize prey with toxins contained within the cells.
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Cnidarians have two body forms—polyp and medusa—which often occur within the life cycle of a single cnidarian. The body of a medusa, commonly called a jellyfish, usually has the shape of a bell or an umbrella, with tentacles hanging downward at the margin. ... Most medusae are slow-swimming, planktonic animals.
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This group of organisms has the following characteristics: they are aquatic, they have tentacles, they have a single body opening they have two body layers and are, for the most part, radially/biradially symmetrical.
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Flatworms are more complex than cnidarians. Cnidarians have two layers of cells, the ectoderm and the endoderm; flatworms have a middle layer called the mesoderm between the other two layers (Fig. 3.16). ... The cells of the ectoderm and endoderm are also more organized than similar cells of cnidarians.
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Regular echinoids have no front or back end and can move in any direction. Irregular echinoids have a definite front and back and do move in a particular direction. This is because regulars and irregulars have very different ways of life.
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If you mean sting other corals around it, in a way. They have a way of regurgitating their own digestive tract to dissolve their neighbors. They seem to get along well with other acans but have been known to attack other corals if they get too close.
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In reality, the planets do not all orbit perfectly in the same plane. Instead, they swing about on different orbits in three dimensional space. For this reason, they will never be perfectly aligned. It's like waiting for a swarm of flies circling your head to all line up.
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Asymmetry. Only members of the phylum Porifera (sponges) have no body plan symmetry. There are some fish species, such as flounder, that lack symmetry as adults. However, the larval fish are bilaterally symmetrical.
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Most cnidarians have the ability to sense changes in light and dark. Box jellies have eyes that are able to form images, making them the most derived cnidarians in terms of sensory biology. Finally, most jellyfish also have a sensory structure called a statocyst that is denser than water.
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Bivalves typically display bilateral symmetry both in shell and anatomy, but there are significant departures from this theme in taxa such as scallops and oysters. ... Bivalves lack a head, radula, and jaws.
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['These are exclusively marine animals.', 'The larval forms show bilateral symmetry and adult forms show radial symmetry.', 'They are triploblastic.', 'It exhibits organ system grade of organisation.', 'They have a true coelom.', 'The body is uniquely shaped.']
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The key to distinguishing brachiopods from bivalves is determining their lines of symmetry. Bivalves have a plane of symmetry that cuts between their two valves. ... Bivalves are often described as having left and right valves. Brachiopods have a plane of symmetry that cuts across the two valves.
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Radial symmetry occurs when the parts of an animal or object are arranged around a central axis, and if they are divided through that axis they create equal parts on either side. ... Chordates, including humans, are also all classified as having bilateral symmetry and can be divided into a left and right side.