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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.
Additionally, female barn swallows, a species where adults have long tail streamers, prefer to mate with males that have the most symmetrical tails. [26] While symmetry is known to be under selection, the evolutionary history of different types of symmetry in animals is an area of extensive debate.
Four classes of arthropods each provide multiple examples, including sea spiders (with 4 to 6 leg pairs, [11] providing two examples) and pauropods (adults with 8 to 11 leg pairs, [12] providing four examples), but most of the examples listed are either millipedes (adults with 11 to 653 leg pairs) [5] [1] or centipedes (adults with 15 to 191 ...
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]
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.
Symmetry in physics has been generalized to mean invariance—that is, lack of change—under any kind of transformation, for example arbitrary coordinate transformations. [17] This concept has become one of the most powerful tools of theoretical physics , as it has become evident that practically all laws of nature originate in symmetries.
Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million in total. Animals range in size from 8.5 millionths of a metre to 33.6 metres (110 ft) long and have complex interactions with each other and their environments, forming intricate food webs .
An unusual feature of sea urchin development is the replacement of the larva's bilateral symmetry by the adult's broadly fivefold symmetry. During cleavage, mesoderm and small micromeres are specified. At the end of gastrulation, cells of these two types form coelomic pouches. In the larval stages, the adult rudiment grows from the left ...