Citizendia
Your Ad Here

"Bilateral symmetry" redirects here. For bilateral symmetry in mathematics, see reflection symmetry. Reflection symmetry, line symmetry, mirror symmetry, mirror-image symmetry, or bilateral symmetry is Symmetry with respect
The elaborate patterns on the wings of butterflies are one example of bilateral symmetry.
The elaborate patterns on the wings of butterflies are one example of bilateral symmetry. A butterfly is an Insect of the order Lepidoptera. Like all Lepidoptera butterflies are notable for their unusual life cycle with a

Symmetry in biology is the balanced distribution of duplicate body parts or shapes. The body plans of most multicellular organisms exhibit some form of symmetry, either radial symmetry or bilateral symmetry. Multicellular organisms are Organisms consisting of more than one cell, and having Differentiated cells that perform specialized functions Symmetry generally conveys two primary meanings The first is an imprecise sense of harmonious or aesthetically-pleasing proportionality and balance such that it reflects beauty or A small minority exhibit no symmetry (are asymmetric).

In nature and biology, symmetry is approximate. Nature, in the broadest sense is equivalent to the natural world, physical universe, material world or material universe. Foundations of modern biology There are five unifying principles For example, plant leaves, while considered symmetric, will rarely match up exactly when folded in half.

Contents

Radial symmetry

These sea anemones display radial symmetry. (Plate from Ernst Haeckel's Kunstformen der Natur).
These sea anemones display radial symmetry. (Plate from Ernst Haeckel's Kunstformen der Natur). Photographic plates preceded Photographic film as a mean of photography Ernst Heinrich Philipp August Haeckel ( February 16, 1834 — August 9, 1919)also written von Haeckel, was an eminent German Kunstformen der Natur ( German: Art Forms of Nature) is a book of lithographic and Autotype prints by German biologist

These organisms resemble a pie where several cutting planes produce roughly identical pieces. An organism with radial symmetry exhibits no left or right sides. They have a top and a bottom (dorsal and ventral surface) only. In fields of Anatomy, anatomical terms of location are descriptive terms to help identify relative positions or directions within a species

Animals

Most radially symmetric animals are symmetrical about an axis extending from the center of the oral surface, which contains the mouth, to the center of the opposite, or aboral, end. This type of symmetry is especially suitable for sessile animals such as the sea anemone, floating animals such as jellyfish, and slow moving organisms such as starfish (see special forms of radial symmetry). Sessile is a term in Biology with two distinct meanings In botany and medicine In Botany, sessile means "without a stalk Sea anemones are a group of water dwelling predatory animals of the order Actiniaria; they are named after the Anemone, a terrestrial Flower Jellyfish are free-swimming members of the phylum Cnidaria. They have several different basic morphologies that represent several different cnidarian classes including the Starfish (also called sea stars) are any Echinoderms belonging to the class Asteroidea. Animals in the phyla cnidaria and echinodermata exhibit radial symmetry (although many sea anemones and some corals exhibit bilateral symmetry defined by a single structure, the siphonoglyph) (see Willmer, 1990). Cnidaria (naɪˈdɛəriə is a phylum containing some 9000 Species of Animals found exclusively in aquatic mostly marine, environments Echinoderms (Phylum Echinodermata) are a phylum of marine Animals (including Sea stars) The siphonoglyph is a ciliated groove at one or both ends of the mouth of Sea anemones and some Corals The siphonoglyph extends into a Pharynx and is used

Plants

Many flowers are radially symmetric (also known as actinomorphic). A flower, also known as a bloom or Blossom, is the reproductive structure found in Flowering plants (plants of the division Magnoliophyta, also Floral symmetry refers to whether and how a Flower can be divided into two or more identical or mirror-image parts Roughly identical petals, sepals, and stamen occur at regular intervals around the center of the flower

Special forms of radial symmetry

Tetramerism

Many jellyfish have four canals and thus exhibit tetramerous radial symmetry. A petal (from Ancient Greek petalon "leaf" "thin plate" regarded as a highly modified leaf is one member or part of the corolla A sepal (from Latin separatus "separate" + petalum "petal" is a part of the flower of Angiosperms or flower plants The stamen ( Plural stamina or stamens, from Latin stamen meaning "thread of the warp " is the male Jellyfish are free-swimming members of the phylum Cnidaria. They have several different basic morphologies that represent several different cnidarian classes including the This form of radial symmetry means it can be divided into 4 equal parts.

Pentamerism

This variant of radial symmetry (also called pentaradial and pentagonal symmetry) arranges roughly equal parts around a central axis at orientations of 72° apart.

Members of the phyla echinodermata (such as starfish and sea urchins) have parts arranged around the axis of the mouth in five equal sectors. Echinoderms (Phylum Echinodermata) are a phylum of marine Animals (including Sea stars) Starfish (also called sea stars) are any Echinoderms belonging to the class Asteroidea. Sea urchins are small globular spiny sea cat animals composing most of class Echinoidea. Being bilaterian animals however, they initially develop biradially as larvae, then gain pentaradial symmetry later on. The Bilateria (ˌbaɪləˈtɪəriə are all animals having a bilateral symmetry, i The radiolarians demonstrate a remarkable array of pentamerism forms. Radiolarians (also radiolaria) are Amoeboid Protozoa that produce intricate Mineral Skeletons typically with a central capsule Examples include the Pentaspheridae, the Pentinastrum group of general in the Euchitoniidae, and Cicorrhegma (Circoporidae).

Apple cut horizontally, showing pentamerism
Apple cut horizontally, showing pentamerism

Flowering plants demonstrate symmetry of five more frequently than any other form. The flowering plants or angiosperms ( Angiospermae or Magnoliophyta) are the most widespread group

Around 1510–1516 A. D. , Leonardo da Vinci determined that in many plants a sixth leaf stands above the first. Leonardo di ser Piero da Vinci ( April 15 1452 – May 2 1519 was an Italian Polymath, having been a scientist Mathematician, Engineer This arrangement later became known as 2/5 phyllotaxy, a system where repetitions of five leaves occur in two turns of the axis. In Botany, phyllotaxis or phyllotaxy is the arrangement of the leaves on the stem of a Plant. This is the most common of all patterns of leaf arrangement.

Various fruits also demonstrate pentamerism, a good example of which is seen in the arrangement of the seed carpels in an apple. A gynoecium (from Ancient Greek gyne, "woman" is the Female reproductive part of a Flower.

Hexamerism and octamerism

Corals and sea anemones (class Anthozoa) are divided into two groups based on their symmetry. Corals are Marine organisms from the class Anthozoa and exist as small Sea anemone –like Polyps typically in colonies of many Sea anemones are a group of water dwelling predatory animals of the order Actiniaria; they are named after the Anemone, a terrestrial Flower Anthozoa is a class within the phylum Cnidaria that contains the Sea anemones and Corals Unlike other cnidarians anthozoans do not have a medusa The most common corals in the subclass Hexacorallia have a hexameric body plan; their polyps have sixfold internal symmetry and the number of their tentacles is a multiple of six. Zoantharia (also known as Hexacorallia, as they have 6-fold symmetry is a subclass of the class Anthozoa within the phylum Cnidaria. In Zoology, a polyp is one of two forms of individuals found in many species of Cnidarians The two are the polyp or hydroid and the medusa. Tentacles can refer to the elongated flexible organs that are present in some animals especially Invertebrates and sometimes to the hairs of the leaves of some insectivorous

Corals belonging to the subclass Octocorallia have polyps with eight tentacles and octameric radial symmetry. Alcyonaria (also known as Octocorallia, as they have 8-fold symmetry is a subclass of the class Anthozoa within the phylum Cnidaria.

Bilateral symmetry

A leaf showing bilateral symmetry.
A leaf showing bilateral symmetry. In Botany, a leaf is an above-ground Plant organ specialized for Photosynthesis.

In bilateral symmetry (also called plane symmetry), only one plane, called the sagittal plane, will divide an organism into roughly mirror image halves (with respect to external appearance only, see situs solitus). A sagittal plane of the human body is an imaginary plane that travels from the top to the bottom of the body dividing it into left and right portions "Mirror Image" is an episode of the Television series The Twilight Zone. Situs solitus refers to the Normal position of thoracic and abdominal organs Thus there is approximate reflection symmetry. Reflection symmetry, line symmetry, mirror symmetry, mirror-image symmetry, or bilateral symmetry is Symmetry with respect Often the two halves can meaningfully be referred to as the right and left halves, e. g. in the case of an animal with a main direction of motion in the plane of symmetry.

Animals

Most animals are bilaterally symmetric, including humans (see also facial symmetry), and belong to the group Bilateria. Symmetry, especially facial symmetry, is one of a number of Aesthetic traits including Averageness and Youthfulness, associated with Health The Bilateria (ˌbaɪləˈtɪəriə are all animals having a bilateral symmetry, i The oldest known bilateral animal is the Vernanimalcula. Vernanimalcula is a fossil believed by some to represent the earliest known member of the Bilateria ( Animals with bilateral symmetry) Most bilateral animals have an identical shape on either side, as if cut by a mirror.

Bilateral symmetry permits streamlining, favors the formation of a central nerve center, contributes to cephalization, and promotes actively moving organisms. Cephalization is an Evolutionary trend whereby nervous tissue, over many generations becomes concentrated toward one end of an organism Bilateral symmetry is an aspect of both chordates and vertebrates.

Plants

Flowers such as members of the orchid and pea families are bilaterally symmetrical (also known as zygomorphic). A pea (inaccurately called a '''sweet pea''' by food distubutors is most commonly the small spherical Seed or the seed-pod of the Legume Pisum Floral symmetry refers to whether and how a Flower can be divided into two or more identical or mirror-image parts The leaves of most plants are also bilaterally symmetrical.

Asymmetry

The notable exception among animals is the phylum Porifera (sponges) which have no symmetry. A phylum ( Plural: phyla) is a Taxonomic rank between Kingdom and above Class. The sponges or poriferans (from Latin porus "pore" and ferre "to bear" are Animals

See also

References

External links

© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org
 Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic