| Planarian | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
 The planarian Schmidtea mediterranea
|
||||||||||||||||
| Scientific classification | ||||||||||||||||
|
Planaria (family Planariidae) are common freshwater, non-parasitic flatworms of the phylum Platyhelminthes, class Turbellaria. Eumetazoa is a Clade comprising all major Animal groups except sponges Characteristics of eumetazoans include true tissues organized into The Platyzoa (ˌplætɨˈzoʊə are a group of Protostome animals proposed by Thomas Cavalier-Smith in 1998 The flatworms (Phylum Platyhelminthes from the Greek πλατύ platy, meaning "flat" and ἕλμινς (root ἑλμινθ- helminth- Turbellaria are a group of generally small ( Platyhelminthes. Tricladida ( Triclads) is an order of the Turbellaria, a group of free-living Flatworms. Freshwater is a word that refers to bodies of water such as Ponds lakes rivers and streams containing low concentrations of dissolved Salts and other Total dissolved The flatworms (Phylum Platyhelminthes from the Greek πλατύ platy, meaning "flat" and ἕλμινς (root ἑλμινθ- helminth- The flatworms (Phylum Platyhelminthes from the Greek πλατύ platy, meaning "flat" and ἕλμινς (root ἑλμινθ- helminth- Turbellaria are a group of generally small ( Platyhelminthes. It should be noted that the term "planaria" is most often used as a common name. It is also the name of a genus within the family Planariidae. Sometimes, it also refers to the genus Dugesia. Dugesia is a genus of Flatworms containing some common representatives of the class Turbellaria [1] It moves by beating cilia on the ventral dermis, allowing it to glide along on a film of mucus. A cilium (plural cilia) is an Organelle found in eukaryotic cells Cilia are tail-like projections extending approximately In fields of Anatomy, anatomical terms of location are descriptive terms to help identify relative positions or directions within a species The dermis is a layer of Skin beneath the epidermis that consists of Connective tissue, and cushions the body from stress and strain In vertebrates mucus is a slippery secretion produced by and covering Mucous membranes It is a viscous Colloid containing Antiseptic enzymes (such as Some move by undulations of the whole body by the contractions of muscles built into the body wall. They exhibit an extraordinary ability to regenerate lost body parts. In Biology, an Organism is said to regenerate a lost or damaged part if the part regrows so that the original function is restored For example, a planarian split lengthwise or crosswise will regenerate into two separate individuals. The size ranges from 3 to 12 mm, and the body has two eye-spots (also known as ocelli) that can detect the intensity of light. An ocellus (plural ocelli) is a type of Photoreceptor organ in animals The eye-spots act as photoreceptors and are used to move away from light sources. Photoreceptor can refer to In anatomy/cell biology Photoreceptor cell: a photosensitive cell most commonly referring to a specialized type of neuron Planaria have three germ layers (ectoderm, mesoderm, and endoderm), and are acoelomate (i. A germ layer is a collection of cells formed during animal Embryogenesis. The ectoderm is the start of a tissue that covers the body surfaces One of the three Germ layers found in the Embryos of Animals more complex than Cnidarians making them Triploblastic. Endoderm, (sometimes called Entoderm) is one of the Germ layers formed during animal Embryogenesis. e. they have a solid body with no body cavity). By the broadest definition a body cavity is any fluid filled space in a Multicellular organism. They have a single-opening digestive tract, consisting of one anterior branch and two posterior branches in freshwater planarians. Because of this three-branched organization, freshwater flatworms are often referred to as triclad planarians.
Planaria are common to many parts of the world and reside in fresh water ponds and rivers. They are also found commonly residing on plants.
The most frequently used in the high school and first-year college laboratories is the brownish Dugesia tigrina. Dugesia is a genus of Flatworms containing some common representatives of the class Turbellaria Other common varieties are the blackish Planaria maculata and Dugesia dorotocephala. Dugesia is a genus of Flatworms containing some common representatives of the class Turbellaria Recently, however, the species Schmidtea mediterranea has emerged as the species of choice for modern molecular biological and genomic research due to its diploid chromosomes and existence in both asexual and sexual strains. Recent genetic screens utilizing double-stranded RNA technology have uncovered 240 genes that affect regeneration in S. mediterranea. Interestingly, many of these genes are found in the human genome (see link below).
Contents |
Anatomy and physiology
The planarian has very simple organ systems. The digestive system consists of a mouth, pharynx, and a structure called a gastrovascular cavity. The mouth, buccal cavity, or oral cavity is the first portion of the Alimentary canal that receives food and begins digestion by mechanically breaking up The pharynx (plural pharynges) is the part of the Neck and Throat situated immediately Posterior to (behind the Mouth and Nasal The mouth is located in the center of the underside of the body. Digestive enzymes secrete from mouth to begin external digestion. The pharynx connects the mouth to the gastrovascular cavity. This structure branches throughout the body allowing nutrients from food to reach all extremities. [1] They eat living or dead small animals that they suck with their muscular mouth. From there, the food passes through the pharynx into the intestines and digesting of the food takes place in the cells lining the intestine, which then diffuses to the rest of the body.
Planare receive oxygen and release carbon dioxide by diffusion. Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement The excretory system is made of many tubes with many flame cells and excretory pores on them. flame cell is a specialized excretory cell found in most "lower" freshwater invertebrates including Nematode, Platyhelminthes (except the tubellarian Flame cells remove unwanted liquids from the body by passing them through ducts that lead to excretory pores where the waste is released on the dorsal surface of the planarian. At the head of the planarian there is a ganglion under the eyespots. In Anatomy, a ganglion (pl ganglia) is a tissue mass. Neurology In neurological contexts ganglia are composed mainly of From the ganglion there are two nerve cords which connect at the tail. A nerve is an enclosed cable-like bundle of peripheral Axons (the long slender projections of Neurons. There are many transverse nerves connected to the nerve cords which make it look like a ladder. With a ladder-like nerve system, it is able to respond in a coordinated manner.
Reproduction
Planaria are hermaphrodites, posessing both testes and ovaries. Thus, they can reproduce asexually with their own gametes or sexually with another planarian. Asexual reproduction is a form of reproduction which does not involve Meiosis, Ploidy reduction or Fertilization. The Evolution of sexual reproduction is a major puzzle The first Fossilized evidence of sexually reproducing Organisms is from Eukaryotes of the Stenian In asexual reproduction, the planarian detaches its tail end and each half regrows the lost parts. However several problems can occur, so this does not happen very often. Instead, in sexual reproduction, each planarian transports its excretion to the other planarian, giving and receiving sperm. The term sperm is derived from the Greek word (σπέρμα sperma (meaning "seed" and refers to the male reproductive cells. Eggs develop inside the body and are shed in capsules. Weeks later, the eggs hatch and grow into adults. Sexual reproduction is desirable because it enhances the survival of the species by mixing the gene pool. Planaria can also reproduce by regeneration. In Biology, an Organism is said to regenerate a lost or damaged part if the part regrows so that the original function is restored Regeneration may occur when a planarian is cut into two halves that may become new planaria. When a planarian is cut in two halves, it is called "tail dropping". Sometimes, a planarian might split in half due to overfeeding.
See also
References
- ^ a b Campbell, Neil A.; Reece, Jane B. (2005). Memory RNA is a now-discredited hypothetical form of RNA that was proposed by James V Mario Benazzi (1902-1997 was an Italian Zoologist at the Instituto di Zoologia e Anatomia Comparata Universita di Pisa Behzad Ghorbani is an Iranian Zoologist, born March 26, 1971, in Tehran. Neil A Campbell (1946– October 21 2004) was an American scientist known best for his textbook Biology. Jane B Reece (born 15 April, 1944) is an American scientist and textbook author Biology. Benjamin Cummings, 1230 pp. ISBN 0-8053-7146-X.
- Alvarado, Alejandro Sánchez, "Quick Guide – Planarians" Current Biology Vol. 14 (R737-8), No. 18 (Retrieved online)
External links
- More information on freshwater planarians and their biology
- More information on the genetic screen to identify regeneration genes
- HD video of a planarium
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic