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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.
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.
Symmetry is also an important consideration in the formation of scales and chords, traditional or tonal music being made up of non-symmetrical groups of pitches, such as the diatonic scale or the major chord.
This is associated with the animal's movement direction and bilateral symmetry. Cephalization of the nervous system has led to the formation of a brain with varying degrees of functional centralization in three phyla of bilaterian animals, namely the arthropods, cephalopod molluscs, and vertebrates.
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 ...
Protostomia (/ ˌ p r oʊ t ə ˈ s t oʊ m i. ə /) is the clade of animals once thought to be characterized by the formation of the organism's mouth before its anus during embryonic development.
Fluctuating asymmetry (FA) is often considered to be the product of developmental stress and instability, caused by both genetic and environmental stressors. The notion that FA is a result of genetic and environmental factors is supported by Waddington's notion of canalisation, which implies that FA is a measure of the genome's ability to successfully buffer development to achieve a normal ...
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.