![]() Radial symmetry equips these sea creatures (which may be sedentary or only capable of slow movement or floating) to experience the environment equally from all directions.įurther subdivision of animals with three germ layers (triploblasts) results in the separation of animals that may develop an internal body cavity derived from mesoderm, called a coelom (sē’-lûm), and those that do not. ![]() This form of symmetry marks the body plans of animals in the phyla Ctenophora and Cnidaria, including jellyfish and adult sea anemones ( Figure 2bc). The two halves of a radially symmetrical animal may be described as the side with a mouth or “oral side,” and the side without a mouth (the “aboral side”). It results in animals having top and bottom surfaces but no left and right sides, or front or back. Radial symmetry is the arrangement of body parts around a central axis, as is seen in a pie. All types of symmetry are well suited to meet the unique demands of a particular animal’s lifestyle. Only a few animal groups display radial symmetry. Asymmetry is a unique feature of Parazoa (Fig. ![]() At a very basic level of classification, true animals can be largely divided into three groups based on the type of symmetry of their body plan: radially symmetrical, bilaterally symmetrical, and asymmetrical.
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