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All bilaterians have some asymmetrical features; for example, the human heart and liver are positioned asymmetrically despite the body having external bilateral symmetry. [14] The bilateral symmetry of bilaterians is a complex trait which develops due to the expression of many genes. The bilateria have two axes of polarity.
Bilateral features in the face and body, such as left and right eyes, ears, lips, wrists and thighs, often show some extent of fluctuating asymmetry. Some individuals show greater asymmetry than others. Fluctuating asymmetry (FA), is a form of biological asymmetry, along with anti-symmetry and direction
Bilateria (/ ˌ b aɪ l ə ˈ t ɪər i ə /) [5] is a large clade of animals characterised by bilateral symmetry during embryonic development.This means their body plans are laid around a longitudinal axis with a front (or "head") and a rear (or "tail") end, as well as a left–right–symmetrical belly and back surface. [6]
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 ...
In developmental biology, left-right asymmetry (LR asymmetry) is the process in early embryonic development that breaks the normal symmetry in the bilateral embryo.In vertebrates, left-right asymmetry is established early in development at a structure called the left-right organizer (the name of which varies between species) and leads to activation of different signalling pathways on the left ...
Facial bilateral symmetry is typically defined as fluctuating asymmetry of the face comparing random differences in facial features of the two sides of the face. [4] The human face also has systematic, directional asymmetry : on average, the face (mouth, nose and eyes) sits systematically to the left with respect to the axis through the ears ...
This plane cuts the body into halves (assuming bilateral symmetry), [3] passing through midline structures such as the navel and spine. It is one of the planes which, combined with the umbilical plane, defines the four quadrants of the human abdomen. [4] The term parasagittal is used to describe any plane parallel or adjacent to a given ...
The inner organs of the trunk are the regions on the body that are least mechanically associated with locomotion and the external body, and so are predicted by the axial twist theory to be the most asymmetric regions of the body. Other bilaterally symmetric animals such as insects and annelids are bilaterally symmetric also on the inside. The ...