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Bilateria (/ ˌ b aɪ l ə ˈ t ɪər i ə / BY-lə-TEER-ee-ə) [5] is a large clade or infrakingdom of animals called bilaterians (/ ˌ b aɪ l ə ˈ t ɪər i ə n / BY-lə-TEER-ee-ən), [6] characterized by bilateral symmetry (i.e. having a left and a right side that are mirror images of each other) during embryonic development.
Animals with bilateral symmetry are classified into a large group called the Bilateria, which contains 99% of all animals (comprising over 32 phyla and 1 million described species). All bilaterians have some asymmetrical features; for example, the human heart and liver are positioned asymmetrically despite the body having external bilateral ...
Animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other. This also means they have a head and a tail (anterior-posterior axis) as well as a belly and a back (ventral-dorsal axis).
Echinoderms differ from chordates and their other relatives in three conspicuous ways: they possess bilateral symmetry only as larvae – in adulthood they have radial symmetry, meaning that their body pattern is shaped like a wheel; they have tube feet; and their bodies are supported by dermal skeletons made of calcite, a material not used by ...
Cephalization is a characteristic feature of the bilaterians, a large group containing the majority of animal phyla. [3] These have the ability to move, using muscles, and a body plan with a front end that encounters stimuli first as the animal moves forwards, and accordingly has evolved to contain many of the body's sense organs, able to detect light, chemicals, and gravity.
Echinoderms evolved from animals with bilateral symmetry. Although adult echinoderms possess pentaradial symmetry, their larvae are ciliated, free-swimming organisms with bilateral symmetry. Later, during metamorphosis, the left side of the body grows at the expense of the right side, which is eventually absorbed.
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.
There is a well-developed cuticle, which may be thick and rigid, giving the animal a box-like shape, or flexible, giving the animal a worm-like shape; such rotifers are respectively called loricate and illoricate. Rigid cuticles are often composed of multiple plates, and may bear spines, ridges, or other ornamentation.