Difference Between Radial and Bilateral Symmetry

Main Difference – Radial vs Bilateral Symmetry

Radial symmetry and bilateral symmetry are two different types of biological symmetries found in organisms. The balanced distribution of the body shapes is referred to as the biological symmetry. Biological symmetry can be divided into several categories such as radial symmetry, spherical symmetry, bilateral symmetry, biradial symmetry and the asymmetry. If the body of an organism can be divided into identical halves in any plane, the particular organism is radially symmetric. When an organism’s body is divided by a particular plane and if the resulting left and right sides are the mirror image of each other, that symmetry is called the bilateral symmetry.  The key difference between radial and bilateral symmetry is that radial symmetry generates identical body halves around the central axis whereas bilateral symmetry generates only two sides as left and right.

1. What is Radial Symmetry
      – Definition, Features, Radially Symmetrical Animals and Plants
2. What is Bilateral Symmetry
      – Definition, Features, Bilaterally Symmetrical Animals and Plants
3. What is the difference between Radial and Bilateral SymmetryDifference Between Radial and Bilateral Symmetry - Comparison Summary

What is Radial Symmetry

Radial symmetry gives rise to similar parts, around the central axis of the body. Most animals that produce radial symmetry are symmetrical along the axis of mouth to aboral end. Therefore, the axis which runs from mouth to the adoral end is referred to as the central axis. Roughly identical pieces can be produced by cutting the organism in several planes along the central axis. Hence, any left or right sides cannot be identified within the organism. It only exhibits top and bottom surfaces due to the gravity. Radially symmetrical animals are classified in the taxon: Radiata. Radiata is assembled in different phyla of the kingdom: Animalia. Most animals living in the sea exhibit radial symmetry. Sessile animals like sea anemone, slow moving organisms like starfish and floating animals like jellyfish are examples of radially symmetrical animals. Cnidaria and Echinodermata animals are also considered as radially symmetric.

Other than animals, plants also exhibit the radial symmetry. Identical flower parts such as petals, sepals and stamens occur symmetrically around the flower axis. Female flower parts like carpel, style and stigma often occur in radial symmetry.

Viruses also exhibit radial symmetry by arranging the protein molecules in their coats symmetrically. Types of the viral coats containing the radial symmetry are icosahedrons, polyhedrons, spheres and ovoids.

Bodies of some organisms form segments around the central axis, creating variations in the radial symmetry. Several variations in the radial symmetry can be identified such as tetramerism, pentamerism, hexamerism and octamerism.    

Difference Between Radial and Bilateral Symmetry

Figure 1: Radial symmetry of the purple sea urchin

What is Bilateral Symmetry

In bilateral symmetry, the body of the organism is divided into two sides as left and right by a basic body plane. Thus, bilateral symmetry is also called the plane symmetry. The plane, which divides the body bilaterally is referred to as the sagittal plane. The two sides generated here are the mirror image of each other. Hence, they exhibit a mirror symmetry in the sagittal plane. The sagittal plane divides the body into left and right vertically. Internal organs may not be symmetrically distributed, but the sense organs and the limb pair can be divided in bilateral symmetry. Since the head is the body part which is located in front of a moving organism, most sensory organs such as eyes and the mouth are concentrated around the head. Thus, moving in one direction generates the front/back difference. The gravity generates the dorsal/ventral difference. But, the left and right are difficult to distinguish.

A majority of organisms, including the human, are bilaterally symmetric. The phylum Echinodermata also contains bilateral symmetry at their larval stage. In plants, some flowers such as orchid and pea families consist of bilateral symmetry.

Main Difference - Radial vs Bilateral Symmetry

Figure 2: The bilateral symmetry of Orchid

Difference Between Radial and Bilateral Symmetry

Definition

Radial Symmetry: The organism’s body generates identical sides in any plane which it is divided along the central axis.

Bilateral Symmetry: The body of the organism generates two sides as left and right along the sagittal plane. The two sides are the mirror image of the other.

Divisions into Left or Right Sides

Radial Symmetry: The body cannot be divided into left and right sides.

Bilateral Symmetry: Sagittal plane divides the body into left and the right sides.

Similar Parts

Radial Symmetry: Similar body parts are arranged in a regular manner around the central axis.

Bilateral Symmetry: Similar body parts are arranged in both left and right sides equally. Thus, each side becomes the mirror image of the other.

Development of the Head

Radial Symmetry: The development of a head in front of the body is rare in radially symmetric animals.

Bilateral Symmetry: The development of a head in front of the organism’s body is a prominent feature in bilaterally symmetric animals.

Examples

Radial Symmetry: Sea urchin, sea anemone, Jellyfish, Starfish, Viral coats

Bilateral Symmetry: Human, insects, crustaceans, centipedes, spiders, orchid flowers

Conclusion

Bilateral symmetry is the most spread biological symmetry among organisms. In bilateral symmetry, left and the right side of the body are the mirror image of each other. Hence, external body parts are distributed between the two sides equally. Radial symmetry, on the other hand, generates similar sides around the central axis. Therefore, the key difference between radial and bilateral symmetry is in the different types of body parts they generate along the axis.

Reference:
1. . Wikipedia, the free encyclopedia. 2017. Accessed 16 Feb. 2017
2. A Dictionary of Biology. Encyclopedia.com. 16 Feb. 2017
3. Undrestanding Evolution. . Accessed 16 Feb. 2017

Image Courtesy:
1. “Withe seaurchin”. By Steven van Tendeloo – via
2. “Ophrys apifera”. By Hans Hillewaert – via

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

Leave a Comment


Related pages


autosomes and sex chromosomesadvantages of colorimetersuspension definition in chemistrystratification in 7 qc toolsdefinition of archetype in literaturecompare and contrast glucose and starchmajor differences between prokaryotes and eukaryoteswhat is a saturated hydrocarbon definitiontyndall effect examplequinoa vs cous cousnovella examplesanother word for effectedmeaning of subordinating conjunctionsexamples of affirmative and negative sentencesdifference between honesty and integritydefinition of producer surplusaltar vs alterwhat is the difference between novel and novelladescriptive essay ppteubacteria vs archaebacteriameaning of tension in physicsfrog or toad differencewhat is the difference between theme and motifhomophone vs homonymnovels and novellaswhat is the difference between sociology and anthropologytypes of adverbwhat causes neuropathy other than diabeteswhat is microevolution and macroevolutionbaseball cinquain poemsdifferences between alligator and crocodilesn2 mechanism stepsmodulus rigiditypatronizing meaningdifference between cream and whipping creamexample of anastrophe in literatureproduction possibility frontier assumptionsadvantages and disadvantages of living in villageexamples of novelladifference between aromatic and aliphaticwhats cytoplasmdifference between 5star and 7 star hotelcell division binary fission and mitosisproperties of mild carbon steelsynedoche exampleswhat is the difference between modern and contemporary dancesarcasm vs ironytransmittance to absorbance formulathe difference between adsorption and absorptionbryophyte definition biologyfutures vs options differencewhat does thermosetting plastic meanis a fairy a mythical creaturehow do the guard cells assist the stomataneutrophils basophils and eosinophils are collectively referred to asincidences or incidentspsychodynamic and psychoanalyticphagocytosis definition biologywhat is the difference between regular and irregular verbsinterrogative pronouns examples in sentenceswhat is the difference between modern and contemporary dancewhat is the difference of alligator and crocodilethud in a sentenceold english bullmastiffmodernism and postmodernism literaturedifference between content analysis and textual analysisadjective determinera concave lens cannot produce a real imagetrade name for sodium bicarbonatedifference in bipap and cpaplight microscope and electron microscope similaritiesbita raysdifference of monocot and dicotirradiation vs radiationparallel resonance circuit theory