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Radial symmetry is especially suitable for sessile animals such as the sea anemone, floating animals such as jellyfish, and slow moving organisms such as starfish; whereas bilateral symmetry favours locomotion by generating a streamlined body. Many flowers are also radially symmetric, or "actinomorphic".
Fish: Dorsal view of right-bending (left) and left-bending (right) jaw morphs [4]. Many flatfish, such as flounders, have eyes placed asymmetrically in the adult fish.The fish has the usual symmetrical body structure when it is young, but as it matures and moves to living close to the sea bed, the fish lies on its side, and the head twists so that both eyes are on the top.
Bilateria (/ ˌ b aɪ l ə ˈ t ɪər i ə /) [5] is a large clade or infrakingdom of animals called bilaterians (/ ˌ b aɪ l ə ˈ t ɪər i ə n /), [6] characterised by bilateral symmetry (i.e. having a left and a right side that are mirror images of each other) during embryonic development.
Animals mainly have bilateral or mirror symmetry, as do the leaves of plants and some flowers such as orchids. [30] Plants often have radial or rotational symmetry, as do many flowers and some groups of animals such as sea anemones. Fivefold symmetry is found in the echinoderms, the group that includes starfish, sea urchins, and sea lilies. [31]
Although radial symmetry is usually given as a defining characteristic in animals that have been classified in this group, there are clear exceptions and qualifications. Echinoderms, for example, exhibit unmistakable bilateral symmetry as larvae, and are now in the Bilateria.
Nettle jelly. A nerve net consists of interconnected neurons lacking a brain or any form of cephalization.While organisms with bilateral body symmetry are normally associated with a condensation of neurons or, in more advanced forms, a central nervous system, organisms with radial symmetry are associated with nerve nets, and are found in members of the Ctenophora, Cnidaria, and Echinodermata ...
This body shape offers an example of secondary front-to-back bilateral symmetry in an organism whose adult anatomy is primarily based on fivefold radial symmetry. The radial symmetry is characteristic of echinoids generally, including the ancestors of sand dollars. The bilateral features evolved as adaptations to a burrowing lifestyle.
Cephalization is an evolutionary trend in animals that, over many generations, the special sense organs and nerve ganglia become concentrated towards the front of the body where the mouth is located, often producing an enlarged head. This is associated with the animal's movement direction and bilateral symmetry.