Planaria: Why Are They Known As Flatworms?
Nature has provided each and every organism a number of unique features to survive successfully in the environment.
Planaria are such organisms which thrive well in nature by acquiring a number of adaptations.
They belong to the phylum Pltayhelminthes.
All the members of this phylum are known as flatworms.
Planaria belong to the order Seriata and family Planariidae.
They are widely distributed in many parts of the world and prefer to dwell in both freshwater as well as saltwater ponds and rivers.
Some species show adaptation towards land and are found to present under the logs of woods, or in soil and on plants in the humid areas.
These animals move with the help of beating of cilia present on the ventral dermis which allows them to glide along a film of mucus.
Some species move by the undulations caused by the contraction of muscles present just below the basement membrane.
Power of regeneration is very well developed.
For example, if a planarian is split either crosswise or lengthwise it regenerates into separate individuals.
The length of the body varies from 1-20 mm and the body bears two eye spots which have the capability of detecting light intensity.
The eye spots act as photoreceptors which help the animal to move away from the source of light.
The body is made up of three germ layers namely ectoderm, mesoderm and endoderm.
They are acoelomate individuals.
Digestive tract has single opening and is made up of one anterior and two posterior branches especially present in the freshwater species.
Just because of the presence of this three branched organization the freshwater individuals are often recognized as triclad flatworms.
They play an efficient role in watercourse ecosytems and are very important bio-indicators.
They are also an important part of laboratory study in the high schools and first year of the college.
The species studied at the college level is the brownish planarianDugesia tigrina.
Other common species are blackish Planaria maculata and Dugesia dorotocephala.
But in the present scenario a species known as Schmidtea mediterranea is used for studying the molecular and genomic details because of its diploid chromosomes and existence of both asexual and sexual strains.
According to a recent report research carried out by using double-stranded RNA technology 240 genes have been isolated that participate in the process of regeneration in S.
mediterranea.
Many of these genes are orthologs in the human genome.
All the members of the family Planariidae are called as planaria but sometimes this term is used for the genus Dugesia.
The anatomy of planarians is very simple.
The digestive system comprises mouth, pharynx and a large gastrovascular cavity.
Mouth is located in the centre of body.
Digestion begins in mouth by the secretion of enzymes.
Pharynx joins mouth with gastrovascular cavity.
Gastrovascular cavity has a number of branches which helps in proper distribution of nutrients to all parts of the body.
They suck either living or dead very small animals from their mouth.
The food passes out from mouth to the intestine through the pharynx where it is digested and the nutrients are diffused to all parts of the body.
They receive oxygen and diffuse carbon dioxide outside the body.
Excretory system is made up of a large number of tubes with many flame cells and excretory pores present on them.
The flame cells remove unwanted liquid from the body and pass the material to the excretory pores which then leave the body of the planarian.
Just beneath the eye spots there is a ganglion.
From the ganglion arise two nerve cords which connect at the tail region.
Just beneath the eye spots there is a dual-lobed mass of nerve tissue designated as brain.
There are number of nerves which connect the main two nerve cords giving a ladder-like appearance to the nervous system.
The body of planarian is soft, flat, wedge-shaped, black, brown or grayish in colouration.
The base o the head is surrounded by two auricles which are sensitive to touch and chemicals.
Circulatory and respiratory systems are wanting.
They are hermaphrodite bearing both testicles and ovaries.
The gamete of one individual combines with the gamete of the other individual.
This type of reproduction is termed as sexual reproduction.
In the asexual reproduction the animal detaches its tail and the half part grows by regeneration into a new individual.
In sexual reproduction eggs develop inside the body inside the capsules.
Eggs hatch and develop into adults.
Sexual reproduction is desirable as it increases the survival rate as well as genetic diversity.
Planaria are such organisms which thrive well in nature by acquiring a number of adaptations.
They belong to the phylum Pltayhelminthes.
All the members of this phylum are known as flatworms.
Planaria belong to the order Seriata and family Planariidae.
They are widely distributed in many parts of the world and prefer to dwell in both freshwater as well as saltwater ponds and rivers.
Some species show adaptation towards land and are found to present under the logs of woods, or in soil and on plants in the humid areas.
These animals move with the help of beating of cilia present on the ventral dermis which allows them to glide along a film of mucus.
Some species move by the undulations caused by the contraction of muscles present just below the basement membrane.
Power of regeneration is very well developed.
For example, if a planarian is split either crosswise or lengthwise it regenerates into separate individuals.
The length of the body varies from 1-20 mm and the body bears two eye spots which have the capability of detecting light intensity.
The eye spots act as photoreceptors which help the animal to move away from the source of light.
The body is made up of three germ layers namely ectoderm, mesoderm and endoderm.
They are acoelomate individuals.
Digestive tract has single opening and is made up of one anterior and two posterior branches especially present in the freshwater species.
Just because of the presence of this three branched organization the freshwater individuals are often recognized as triclad flatworms.
They play an efficient role in watercourse ecosytems and are very important bio-indicators.
They are also an important part of laboratory study in the high schools and first year of the college.
The species studied at the college level is the brownish planarianDugesia tigrina.
Other common species are blackish Planaria maculata and Dugesia dorotocephala.
But in the present scenario a species known as Schmidtea mediterranea is used for studying the molecular and genomic details because of its diploid chromosomes and existence of both asexual and sexual strains.
According to a recent report research carried out by using double-stranded RNA technology 240 genes have been isolated that participate in the process of regeneration in S.
mediterranea.
Many of these genes are orthologs in the human genome.
All the members of the family Planariidae are called as planaria but sometimes this term is used for the genus Dugesia.
The anatomy of planarians is very simple.
The digestive system comprises mouth, pharynx and a large gastrovascular cavity.
Mouth is located in the centre of body.
Digestion begins in mouth by the secretion of enzymes.
Pharynx joins mouth with gastrovascular cavity.
Gastrovascular cavity has a number of branches which helps in proper distribution of nutrients to all parts of the body.
They suck either living or dead very small animals from their mouth.
The food passes out from mouth to the intestine through the pharynx where it is digested and the nutrients are diffused to all parts of the body.
They receive oxygen and diffuse carbon dioxide outside the body.
Excretory system is made up of a large number of tubes with many flame cells and excretory pores present on them.
The flame cells remove unwanted liquid from the body and pass the material to the excretory pores which then leave the body of the planarian.
Just beneath the eye spots there is a ganglion.
From the ganglion arise two nerve cords which connect at the tail region.
Just beneath the eye spots there is a dual-lobed mass of nerve tissue designated as brain.
There are number of nerves which connect the main two nerve cords giving a ladder-like appearance to the nervous system.
The body of planarian is soft, flat, wedge-shaped, black, brown or grayish in colouration.
The base o the head is surrounded by two auricles which are sensitive to touch and chemicals.
Circulatory and respiratory systems are wanting.
They are hermaphrodite bearing both testicles and ovaries.
The gamete of one individual combines with the gamete of the other individual.
This type of reproduction is termed as sexual reproduction.
In the asexual reproduction the animal detaches its tail and the half part grows by regeneration into a new individual.
In sexual reproduction eggs develop inside the body inside the capsules.
Eggs hatch and develop into adults.
Sexual reproduction is desirable as it increases the survival rate as well as genetic diversity.