Radiata
Organisms that show radial symmetry such that they can be divided into several identical parts when cut through the central axis are referred to as radiata or radiates. These animals do not have a left or right side to their body but do exhibit a top and a bottom or a front and a back. They are diploblastic in nature, meaning they possess two germ layers: endoderm and ectoderm. Animals belonging to the phylum Cnidaria show radial symmetry. Examples include jellyfish and sea anemone which follow a sessile lifestyle. The phylum Echinodermata, which shows triploblastic arrangement are radially symmetrical in their adult stage as can be seen in starfish.
Bilateria
Bilateria or bilaterians are animals that show biradial symmetry,meaning they have a left and right side of body that are mirror images of each other. All of the higher animals excluding sponges, ctenophores, cnidarians and placozoans are bilaterians. They are triploblastic in nature, having three germ layers: endoderm, mesoderm and ectoderm. They possess complete digestive tracts with a separate mouth and anus. In terms of body cavities, they can either be coelomates, pseudocoelomates or acoelomates.
Radiata vs Bilateria
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The animals that can be divided into several identical halves when cut along the central axis are referred to as radiata. |
The animals that can be divided into two identical halves along a single axis only are referred to as bilateria. |
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Radial symmetry |
Bilateral symmetry |
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Two |
Three |
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Diploblastic |
Triploblastic |
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Coelenterates and Echinoderms |
All of the higher organisms |
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Do not have a left and right side of the body. |
They have an identical left and right side of body. |
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They do not have coelom. |
They can be either coelomates, pseudocoelomates or acoelomates. |
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