Symmetry in biology

bilateral symmetryradial symmetrybilaterally symmetricalbilateralsymmetryradially symmetricalbilaterally symmetricradially symmetricbilaterallypentamerism
Symmetry in biology is the balanced distribution of duplicate body parts or shapes within the body of an organism.wikipedia
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Body plan

bauplanBody formbodyplan
The body plans of most multicellular organisms exhibit some form of symmetry, whether radial, bilateral, or spherical.
This term, usually applied to animals, envisages a "blueprint" encompassing aspects such as symmetry, segmentation and limb disposition.

Radiata

coelenteratecoelenteratesradiates
Symmetry was once important in animal taxonomy; the Radiata, animals with radial symmetry, formed one of the four branches of Georges Cuvier's classification of the animal kingdom.
Radiata or Radiates is a historical taxonomic rank that was used to classify animals with radially symmetric body plans.

Animal

Animaliaanimalsmetazoa
Symmetry was once important in animal taxonomy; the Radiata, animals with radial symmetry, formed one of the four branches of Georges Cuvier's classification of the animal kingdom.
Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan.

Cnidaria

cnidariancnidarianscnidarian venoms
Animals in the phyla Cnidaria and Echinodermata are radially symmetric, although many sea anemones and some corals have bilateral symmetry defined by a single structure, the siphonoglyph.
They have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes.

Echinoderm

Echinodermataechinodermsechinoids
Animals in the phyla Cnidaria and Echinodermata are radially symmetric, although many sea anemones and some corals have bilateral symmetry defined by a single structure, the siphonoglyph. Among animals, only the echinoderms such as sea stars, sea urchins, and sea lilies are pentamerous as adults, with five arms arranged around the mouth. The phylum Echinodermata, which includes starfish, sea urchins and sand dollars, is unique among animals in having bilateral symmetry at the larval stage, but pentamerism (fivefold symmetry) as adults.
The adults are recognizable by their (usually five-point) radial symmetry, and include such well-known animals as starfish, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or "stone lilies".

Bilateria

bilaterianbilateriansbilateral animals
Being bilaterian animals, however, they initially develop with mirror symmetry as larvae, then gain pentaradial symmetry later.
The bilateria or bilaterians are animals with bilateral symmetry as an embryo, i.e. having a left and a right side that are mirror images of each other.

Radial

Radial (disambiguation)
The body plans of most multicellular organisms exhibit some form of symmetry, whether radial, bilateral, or spherical.

Sea urchin

Echinoideasea urchinsechinoid
Among animals, only the echinoderms such as sea stars, sea urchins, and sea lilies are pentamerous as adults, with five arms arranged around the mouth. The phylum Echinodermata, which includes starfish, sea urchins and sand dollars, is unique among animals in having bilateral symmetry at the larval stage, but pentamerism (fivefold symmetry) as adults.
Like other echinoderms, urchins have fivefold symmetry as adults, but their pluteus larvae have bilateral (mirror) symmetry, indicating that they belong to the Bilateria, the large group of animal phyla that includes chordates, arthropods, annelids and molluscs.

Crinoid

Crinoideacrinoidssea lilies
Among animals, only the echinoderms such as sea stars, sea urchins, and sea lilies are pentamerous as adults, with five arms arranged around the mouth.
The theca is pentamerous (has five-part symmetry) and is homologous with the body or disc of other echinoderms.

Octopus

octopusesOctopodaoctopodes
The octopus, however, has bilateral symmetry, despite its eight arms.
Like other cephalopods, the octopus is bilaterally symmetric with two eyes and a beak, with its mouth at the center point of the eight limbs ("tentacle" is used as an umbrella term for cephalopod limbs; however, within a teuthological context, "arm" is used to refer to such limbs while "tentacle" is reserved for feeding appendages not found on octopuses).

Anthozoa

anthozoancoralanthozoans
Hexamerism is found in the corals and sea anemones (class Anthozoa) that are divided into two groups based on their symmetry.
The two main subclasses of Anthozoa are the Hexacorallia, members of which have six-fold symmetry and includes the stony corals, sea anemones, tube anemones and zoanthids; and the Octocorallia, which have eight-fold symmetry and includes the soft corals and gorgonians (sea pens, sea fans and sea whips), and sea pansies.

Symmetry

symmetricalsymmetricsymmetries
In nature and biology, symmetry is always approximate.
Humans find bilateral symmetry in faces physically attractive; it indicates health and genetic fitness.

Cephalization

cephalisationforming a headcephalic
A distinct head, with sense organs connected to a central nervous system, therefore (on this view) tends to develop (cephalization).
This is associated with movement and bilateral symmetry, such that the animal has a definite head end.

Petal

corollapetalscorollas
Roughly identical flower parts – petals, sepals, and stamens – occur at regular intervals around the axis of the flower, which is often the female part, with the carpel, style and stigma.
The petal whorl or corolla may be either radially or bilaterally symmetrical (see Symmetry in biology and Floral symmetry).

Sand dollar

Clypeasteroidasand dollarspansy shell
The phylum Echinodermata, which includes starfish, sea urchins and sand dollars, is unique among animals in having bilateral symmetry at the larval stage, but pentamerism (fivefold symmetry) as adults.
The test consists of calcium carbonate plates arranged in a fivefold radial pattern.

Orchidaceae

orchidorchidsorchid family
Flowers in some families of flowering plants, such as the orchid and pea families, and also most of the figwort family, are bilaterally symmetric (zygomorphic).
Among these are: bilateral symmetry of the flower (zygomorphism), many resupinate flowers, a nearly always highly modified petal (labellum), fused stamens and carpels, and extremely small seeds.

Sagittal plane

sagittalsagittal sectionparasagittal
In bilateral symmetry (also called plane symmetry), only one plane, called the sagittal plane, divides an organism into roughly mirror image halves.

Floral symmetry

zygomorphicactinomorphicstar-symmetrical
Flowers in some families of flowering plants, such as the orchid and pea families, and also most of the figwort family, are bilaterally symmetric (zygomorphic). Many flowers are radially symmetric or actinomorphic.
Actinomorphic flowers are also called radially symmetrical or regular flowers.

Starfish

Asteroideasea starsea stars
Among animals, only the echinoderms such as sea stars, sea urchins, and sea lilies are pentamerous as adults, with five arms arranged around the mouth. The phylum Echinodermata, which includes starfish, sea urchins and sand dollars, is unique among animals in having bilateral symmetry at the larval stage, but pentamerism (fivefold symmetry) as adults. Radial symmetry is especially suitable for sessile animals such as the sea anemone, floating animals such as jellyfish, and slow moving organisms such as starfish.
The larvae of echinoderms have bilateral symmetry, but during metamorphosis this is replaced with radial symmetry, typically pentameric.

Ctenophora

ctenophorecomb jelliesctenophores
Biradial symmetry is a combination of radial and bilateral symmetry, as in the ctenophores.
Since the body of many species is almost radially symmetrical, the main axis is oral to aboral (from the mouth to the opposite end.) However, since only two of the canals near the statocyst terminate in anal pores, ctenophores have no mirror-symmetry, although many have rotational symmetry.

Siphonoglyph

Animals in the phyla Cnidaria and Echinodermata are radially symmetric, although many sea anemones and some corals have bilateral symmetry defined by a single structure, the siphonoglyph.
The presence of a siphonoglyph (or two siphonoglyphs) in several anthozoans (including species from the orders Zoantharia, Ceriantharia, Antipitharia, and Octocorallia) introduces an element of bilateral symmetry into the particular species' body plan (Beklemishev 1969).

Facial symmetry

facial asymmetrysymmetricalEchoism (facial symmetry)
Facial symmetry influences human judgements of human attractiveness.

Metamorphosis

metamorphosemetamorphosedmetamorphosing
Adult flatfish rest on one side, and the eye that was on that side has migrated round to the other (top) side of the body.
Many species of flatfish begin their life bilaterally symmetrical, with an eye on either side of the body; but one eye moves to join the other side of the fish – which becomes the upper side – in the adult form.

Organism

organismsflora and faunaliving organisms
Symmetry in biology is the balanced distribution of duplicate body parts or shapes within the body of an organism.