Thursday, 26 December 2013


Since its inception ,science has served mankind with its full strength . Continuing its Legacy of serving , science gave us some new methods and processes in 2013  as well.This annual list of groundbreaking scientific achievements, selected by and its international nonprofit publisher, AAAS, also includes major breakthroughs in solar cell technologies, genome-editing techniques and vaccine design strategies, to name a few.
“This year there was no mistaking the immense promise of cancer immunotherapy,” Tim Appenzeller, chief news editor of the journal saidin a press release by the American Association for the Advancement of Science (AAAS). “So far, this strategy of harnessing the immune system to attack tumours works only for some cancers and a few patients, so it's important not to overstate the immediate benefits. But many cancer specialists are convinced that they are seeing the birth of an important new paradigm for cancer treatment.”
 There is still plenty of uncertainty regarding how many patients will benefit from these therapies, most of which remain experimental — and for which forms of cancer they will work best, the release noted. Scientists are busy trying to identify biomarkers that might offer answers, and thinking of ways to make treatments more potent. But a new chapter in cancer research and treatment has begun. The journal’s list of nine other groundbreaking scientific achievements from the past year follows.

CRISPR: Akin to the discovery of the microscope in the 1920 that “touched off a revolution in surgical procedures,” the discovery of a bacterial protein — Cas9 — gives “researchers the equivalent of a molecular surgery kit for routinely disabling, activating, or changing genes,” the paper notes.
Though CRISPR, the gene-editing technique was discovered in bacteria, researchers use it as a scalpel for surgery on individual genes. Its popularity soared this year — with over 50 publications in 10 months — as more than a dozen teams of researchers used it to manipulate the genomes of various plant, animal and human cells.
Cloning human embryos: After years of failure, researchers were able to derive stem cells from cloned human embryos this year. Scientists were able to clone sheep, mice, pigs, dogs and other animals, but human cells proved really tricky.
But in 2007, researchers at the Oregon National Primate Research Center in Beaverton succeeded in cloning monkey embryos and extract embryonic stem cells. In the process they realised that caffeine plays an important role in the process, stabilizing key molecules in delicate human egg cells.
CLARITY: This imaging technique, which renders brain tissue transparent by “by removing the fatty, light-scattering lipid molecules that form cellular membranes.” The lipids are replaced with molecules of “clear gel” but all neurons (as well as other brain cells) are left intact and on full display. This has changed the way researchers look at this intricate organ in 2013.
According to the paper, researchers say the “advance could speed up by 100-fold tasks such as counting all the neurons in a given brain region and could make traditional methods of imaging post-mortem brain tissue irrelevant.” Currently, the technique is limited to small amounts of tissue.
Mini-organs: Researchers made remarkable progress growing mini human-like “organoids” in vitro this year. These included liver buds, mini-kidneys and tiny brains. miniaturized human organs may prove to be much better models of human disease than animals.
If it is a challenge to “coax stem cells to grow into specific tissues” prodding pluripotent stem cells to develop into organized structures has been nearly impossible. Not any more. Researchers in spectacular style were able to grow a variety of “organoids” in the lab — liver buds, mini-kidneys, and, most remarkably, rudimentary human brains.
Cosmic rays traced to supernova remnants: Although originally detected 100 years ago, scientists have not been sure where the high-energy particles from outer space known as cosmic rays come from. This year, they finally tied the rays to debris clouds left by supernovae, or exploding stars.
Perovskite solar cells: A new generation of solar-cell materials, cheaper and easier to produce than those in traditional silicon cells, garnered plenty of attention this past year. Perovskite cells are not as efficient as commercial solar cells yet, but they are improving very quickly.
Structural biology guides vaccine design: This year, researchers used the structure of an antibody to design an immunogen — the main ingredient of a vaccine — for a childhood virus that hospitalizes millions each year. It was the first time that structural biology led to such a powerful tool for fighting disease.
Our microbes, our health: Research on the trillions of bacterial cells that call the human body home made it clear how much these microbes do for us. "Personalized" medicine will need to take these microbial tenants into account in order to be effective.
Why we sleep: Studies with mice showed that the brain cleans itself — by expanding channels between neurons and allowing more cerebrospinal fluid to flow through — much more efficiently during sleep. The finding suggests that restoration and repair are among the primary purposes of catching Z's.
Let's hope these processes make their targetted outcome in passage of time.

Shailesh kr Shukla

Indigenous device detecting early cervical cancer launched

The Union Health and Family Welfare Ministry on Monday launched indigenous equipment that can detect early cervical cancer and be used even by healthcare workers with basic training.
The device AV Magnivisualizer which was developed by the Institute of Cytology and Preventive Oncology under the Indian Council of Medical Research (ICMR) has 95 per cent accuracy for detecting pre-cancerous lesions. Randomised clinical control trials have confirmed its efficacy in reducing incidence and mortality of the disease. It can be made available in remote rural areas.
This is a user-friendly device which costs about Rs 10,000 as against the present devices which cost between Rs 8-10 lakh and are beyond the reach of most people.
The device has a white light source with variable interchangeable magnification and can be operated on a 12- volt battery in rural and semi-urban areas where electric supply is not regular. Magnivisualizer has been found to pick up 1.5 times more high-grade pre-cancerous lesions than the ordinary tungsten light.
“The ICMR is initiating studies to assess its applicability even for oral pre-cancerous and cancerous lesions,” V.M. Katoch, Director General of ICMR, said.
Cervical cancer is the most common malignancy among Indian women, particularly those who marry early. Current estimates indicate that approximately 1.32 lakh new cases are diagnosed and 74,000 deaths occur annually in India, accounting for nearly one-third of global cervical cancer deaths.
Launching the device, Union Health and Family Welfare Minister Ghulam Nabi Azad said it would be available in the market within the next 8-9 months and efforts would be made to provide them up to the Community Health Centres in the initial phase. In the next phase it would be made available in the Primary Health Centres (PHC), where cervical cancer cases go undetected. “We are aware of the shortage of human resource at the PHC level,” Mr. Azad said, adding that efforts would be made to train the available manpower at both levels until the device reaches them.
Cervical cancer takes about a decade to fully develop and is often detected when it has spread substantially. It starts from a pre-cancer stage called dysplasias and early detection and appropriate treatment at this stage can halt its progression, resulting in decreased incidence or mortality.
At present, cytology screening or Pap Smear is available only in advanced cytology centres, Regional Cancer Centres and some medical colleges. The required infrastructure, trained manpower and related mechanism for initial screening are not available to carry out population-based screening at the State or the national level.

The cervical cancer is the most serious problem among women in Indian as well as World and also the cause of heavy toll.
Shailesh kr shukla


Amphibia refers to "double life", or life in water and on land
Includes the salamanders, frogs, toads, and caecilians with approximately 3,900 spp.
Characterized by:
  • Being tetrapods (4 limbs) that facilitate moving about on land - these limbs evolved from the pectoral and pelvic fins
  • Skin is thin, soft, glandular and magid (lack scales except in the caecilians) - skin of caecilians with scales similar to those of fish
  • Ectothermic
  • Both gill and lung breathers - usually gills in the larval stage, replaced by lungs in the adult; cutaneous respiration in many
  • Three-chambered heart with two atria and one ventricle
Amphibian reproduction variable
  • fertilization may be internal or external
  • egg-layers (oviparous) but may have modifications associated with development
  • egg anamniotic - doesn't have a shell but covered with a series of gelatinous layers
  • hatchling in aquatic larval form which breath by gills
  • most larvae herbivorous, some omnivorous to carnivorous
  • larval stage may last from 10 days to 20+ years
Amphibians are
  • unable to regulate body temperature
  • skin types limit distribution to warm, moist climates (i.e. tropics, subtropics, and temperate zones)
  • most US species in the south; not found in dry areas
  • generally limited to freshwater lakes, streams, ponds - none are true marine forms
Amphibians are represented by three subclasses
  • Subclass Labrinthodontia - looked like a salamander
  • represented by genus Ichthyostega (fish with feet or legs)
  • identified by specific labronthodont tooth
  • Subclass Lepospondyli
  • named for vertebral type with three fused parts
  • Subclass Lissamphibia - contains all living specimens
  • where living amphibians evolved is not clear - modern (living) amphibians appeared in Triassic

Life History and Ecology

The name amphibian means "double life", and is given to members of this group for the double life that they lead. For while adult amphibians usually live on land, their soft eggs must be laid in the water. The eggs shown at left have just been shed by the female. This means that they have not yet been fertilized; the male sheds sperm over the eggs after they have been released into the water.

Young amphibians, like the larval frog or tadpole pictured here, spend their early years in the water, breathing through gills in the side of their head in much the same way as fish do. In many ways they resemble fish more than they resemble their parents, for they have no legs, and swim by wriggling their tail. As they mature, amphibians will usually lose their gills and develop legs. A number of salamanders, such as the North American "mudpuppy" and the Mexican axolotl, develop legs but retain their larval gills and stay in the water throughout their lifetimes. This is a classic example of an evolutionary phenomenon known as neoteny -- the retention of larval or juvenile features in mature adults.

Most amphibians have soft skin which easily absorbs water. This puts them in very close contact with their surroundings. It also makes them particularly susceptible to certain man-made toxins and pollutants. This may be why the number of amphibian species, and the size of many amphibian populations, has been declining in recent years. Amphibians, like the proverbial "canary in a coal mine," may be among the first organisms to suffer from the effects of global pollution and climate change -- providing an early warning of environmental degradation.


Shailesh kr Shukla

The name Rodentia is derived from the Latin verb rodere (to gnaw), in allusion to the gnawing habits of the group. Among North American mammals, rodents are unique in that the incisors are reduced in number to one on each side above and below, in the absence of canines, and in the presence of never more than two premolars in each jaw above and one below. The dental formula varies from: I 1/1, C 0/0, Pm 0/0, M 3/3 X 2 = 16 to I 1/1, C 0/0, Pm 2/1, M 3/3 X 2 = 22. Most animals assigned to the order are small in size; some, for example the beaver, may exceed 25 kg in weight. Rodents comprise more than one-third of the known kinds of mammals, and individually they are the most abundant mammal in many sections of the world. Sixty-four species of native rodents occupy Texas, making this the most diverse group of mammals in our state.

In habits, members of this order are diverse. Most of them are nocturnal or crepuscular; ground squirrels and tree squirrels are strictly diurnal; others may be active either by day or by night. Considerable adaptive radiation occurs in the group. Some species (pocket gopher) are fossorial; others are aquatic (beaver), arboreal (tree squirrel), volant (flying squirrel), or terrestrial (cotton rat). Most rodents feed on vegetation, but a few species, notably the grasshopper mouse, feed extensively upon animal matter. Most rodents are active throughout the year, but others, notably ground squirrels, may hibernate for several months.

With over 2000 living species placed in about 30 families, rodents are by far the largest order of mammals, at least in terms of number of taxa (well over 40% of mammalian species belong to the order Rodentia!). Rodents range in size from pygmy mice weighing 5 gms to capybaras, the largest of which weigh over 70 kg. They are found around the world except in Antarctica, New Zealand, and on some oceanic islands. Ecologically, they are incredibly diverse. Some species spend their entire lives above the ground in the canopy of rainforests; others seldom emerge from beneath the ground. Some species are highly aquatic, while others are equally specialized for life in deserts. Many are to some degree omnivorous; others are highly specialized, eating, for example, only a few species of invertebrates or fungi.
Despite their morphological and ecological diversity, all rodents share one characteristic: their dentition is highly specialized for gnawing. All rodents have a single pair of upper and a single pair of lower incisors, followed by a gap ( diastema), followed by one or more molars or premolars. No rodent has more than one incisor in each quadrant, and no rodent has canines. Rodent incisors are rootless, growing continuously. Their anterior and lateral surfaces are covered with enamel, but their posterior surface is not. During gnawing, as the incisors grind against each other, they wear away the softer dentine, leaving the enamel edge as the blade of a chisel. This "self sharpening" system is very effective and is one of the keys to the enormous success of rodents.
The condition of a dominant pair of incisors used for gnawing, followed by a long diastema, is not unique to rodents, and in fact rodents are relative latecomers to this condition (even though as a group, they have a very old fossil history, going back to Paleocene times). It is even seen in a group of therapsids (ancestors of mammals), the tritylodonts, which lived during the Jurassic. Multituberculates, a very large and successful but now extinct group of early mammals, had a similar pattern. So do wombatshyraxesaye-ayes, and lagomorphs, to give a few examples chosen from modern mammals. Rodents have specialized in gnawing to an extreme, however, seen in few or no other groups of vertebrates.
The main muscle used in chewing by rodents is the masseter, and the rodents can be divided into several groups based on exactly how they use these muscles. These groupings have been used in several ways in the past to classify rodents.
Lodgepole Chipmunk
Rodents are found native on all continents except Antarctica. One particular family of rodents, the Muridae, contains over 1100 species: over a quarter of all mammal species are rats, mice, voles, muskrats, lemmings, hamsters, gerbils, and other members of the Muridae. However, rodents show perhaps their greatest diversity of form in South America, which was an isolated continent for much of the Cenozoic. A few of these distinctive South American rodents include mountain viscachas, rabbit-like forms that inhabit dry mountainous regions; Patagonian cavies, very rabbit-like, fast-running forms with elongated ears and short tails; the coypu or nutria, a large marsh-dwelling rodent that has been introduced into North America and is hunted for its fur; and various burrowing forms such as pacas and tuco-tucos. Other South American rodents include guinea pigs, chinchillas, and New World porcupines (one species of which has dispersed into North America). The capybara (shown 
at left), yet another South American species, is the largest living rodent. About the size of a pig, and reaching a maximum weight of 50 kg (110 pounds), the capybara is truly a rodent of unusual size. Capybaras live along rivers in the llanos (plains) of South America, and are often hunted or even ranched for their meat.
Despite their great species diversity, all rodents share common features. Rodents have a single pair of incisors in each jaw, and the incisors grow continually throughout life. The incisors have thick enamel layers on the front but not on the back; this causes them to retain their chisel shape as they are worn down. Behind the incisors is a large gap in the tooth rows, ordiastema; there are no canines, and typically only a few molars at the rear of the jaws. Rodents gnaw with their incisors by pushing the lower jaw forward, and chew with the molars by pulling the lower jaw backwards. In conjunction with these chewing patterns, rodents have large and complex jaw musculature, with modifications to the skull and jaws to accommodate it. Like some other mammal taxa, but unlike rabbits and other lagomorphs, male rodents have a baculum (penis bone). Most rodents are herbivorous, but some are omnivorous, and others prey on insects. Rodents show a wide range of lifestyles, ranging from burrowing forms such as gophers and mole rats to tree-dwelling squirrels and 
Prairie dogs
gliding "flying" squirrels, from aquatic capybaras and muskrats to desert specialists such as kangaroo rats and jerboas, and from solitary organisms such as porcupines to highly social organisms living in extensive colonies, such as prairie dogs (left) and naked mole rats.
Rodents cost billions of dollars in lost crops each year, and some are carriers of human diseases such as bubonic plague, typhus, and Hanta fever. However, various rodent species are economically important as sources of food or fur in many parts of the world, and others are used extensively in biomedical research.

Shailesh kr Shukla

Wednesday, 25 December 2013

The Phylum Hemichordata

Characteristics of Hemichordata:-
1)Bilaterally symmetrical.
2)Body has more than two cell layers, tissues and organs.
3)Body cavity a true coelom.
4)Body possesses a through gut, straight or U-shaped, with an anus.
5)Body divided into three sections, a proboscis, a collar and a trunk.
6)Nervous system normally diffuse, but variable.
7)Has a partially open circulatory system.
8)Possesses glomerulus as an excretory organ.
9)Reproduction normally sexual and gonochoristic.
10)Feeds on fine particles in the water.
11)All live marine environments.


The bodies of Hemichordates are divided into three parts, proboscis, collar and trunk. They have open circulatory systems and a complete digestive tract but the musculature in their gut is very poorly developed, and food is mostly transported through it by using the cilia that cover its inside surface.
They have a diverticulum of the foregut called a stomochord, previously thought to be related with the chordate notochord, but this is most likely the result ofconvergent evolution rather than homology. A hollow neural tube exists among some species (at least in early life), probably a primitive trait they share with the common ancestor of chordata and the rest of the deuterostomes.


The hemichordates give us the closest extant phylogenetic relative between the chordates and other invertebrates. Thus these marine worms, described to be the sister group of such animals as sea urchins, are of great importance to the scientific community interested in knowing the origins of chordate development. There are several species classified as hemichordates and there exists a moderate diversity of embryological development between these species. Hemichordates are classically known to develop in two ways both directly and indirectly.[1] Hemichordates are a phylum composed of two classes the enteropneusts and the pterobranchs, both are forms of marine worm. The enteropneusts have two developmental strategies direct and indirect development. The indirect way of development is known to end in an extended pelagic plankotrophic tornaria larval stage, which means that this hemichordate exists in a larval stage that feeds on plankton before turning into an adult worm.[2] Those species that are direct developing bypass this prolonged larval stage and develop directly into an adult worm. The following details the development of two popularly studied species of the hemichordata phylumSaccoglossus kowalevskii and Ptychodera flavaSaccoglossus kowalevskii is a direct developer and Ptychodera flava is an indirect developer. Most of what has been detailed in Hemichordate development has come from hemichordates that develop directly.

They are all marine worm-like animals. There are only about 90 known species all of which are benthic, (living on the sea floor) in their adult form. The smallest species are only a few millimetres long and the largest,Balanoglossus gigas can reach lengths of 1.5 metre (4.7 feet). All known species feed on small particles of organic matter either as filter feeders of as substrate eaters. They have a wide distribution and can be found in most of the worlds waters both in shallow coastal waters and in the deeper seas.
The basic body plan is tripartite (in three sections). The first section is called the 'Protosome'. This is a modified proboscis and in many species it is short, it is these species that have given the Hemichordates their common name of 'Acorn Worms'. The protosome is followed by a 'collar' which bears tentacles in the Pterobranchia but not in the Enteropneusta. Behind this is a 'trunk' which contains the digestive and reproductive organs.
The phylum is divided into two classes, the Pterobranchia and the Enteropneusta. The two classes share some attributes but are quite different in others.

Class Enteropneusta

The Enteropneusts, with more than 70 species, comprise the majority of the Hemichordates, they are the typical Acorn Worms. They live in burrows in the substrate (mud or fine sand) or under rocks, in both shallow and deeper waters. Feeding is either filter feeding or substrate eating. The proboscis is small in both types and the collar is very small.
Substrate eaters like Balanoglossus clavigerus from the Mediterranean are generally larger than filter feeders. They consume large amounts of mud and or sand and digest the organic matter within it. They deposit their wastes on the surface much like earthworm castes. Their burrows may have several openings at one end. They seldom leave their burrows.
Filter feeders have mucous secreting glands and numerous cilia on their proboscis. The proboscis is held out of the burrow entrance and organic particles are caught in the mucous which is swept to the mouth by the beating of the cilia. These species can cover their mouth with their collar and thus avoid eating inorganic or otherwise undesirable materials.
The digestive system is a through gut ending in a terminal anus. Behind the mouth is a buccal cavity which leads into a pharynx which possess gill slits. These gill slits are believed to be used primarily to assist gaseous exchange (respiration). The Pharynx leads into an oesophagus which in turn leads to an intestine which is the main site of digestion. The intestine leads ultimately to the anus.
Gaseous exchange occurs over the whole body as well as in the pharyngeal slits. The blood is colourless and has no respiratory pigments. It is forced through the animal's few vessels by the beating of a muscular heart that forces blood through the central sinus. The heart constricts the sinus, but the blood does not actually enter the heart so it is not a heart in the strictest sense. The blood passes through two longitudinal blood vessels and a series of sinuses.
The nervous system derives from a sub-epidermal net and is thickened in the mid-dorsal region of the proboscis and the mid-ventral area of the trunk into hollow nerve cords. In the collar their are giant nerve fibres, but their function is poorly understood and the animal can survive reasonable well without them.
Reproduction can occur as a result of fragmentation of the adults body, however it normally involves the two sexes and egg fertilisation. Both sexes have numerous gonads and fertilisation is external. The females extrude egg masses onto the surface of the substrate from within their burrows (2,000 to 3,000 eggs at a time). The males also release their sperm into the water, the sperm swim and seek out the eggs which it is believed they detect chemically. The fertilised egg develops into a 'tornaria' larvae and lives as part of the plankton (floating in the sea) for several weeks until it undergoes a metamorphosis into the 3 body sections that the adult possesses and sinks to the sea-floor.

Class Pterobranchia

With only between 10 and 20 species the Pterobranchia make up less than one fifth of the Hemichordates. They are small animals ranging in size from 1 to 12 millimetres in length. Pterobranchs live in much deeper water than the Enteropneusts, this and their soft bodies means that they are difficult to study and much less is known about their ecology.
The proboscis is modified into into a shield which secretes the collagenous burrow in those species that live in one. It is also used as an organ of locomotion, much in the way a snail uses its foot, both for movement inside and outside the burrow.
The collar is modified to produce between 1 and 9 pairs of tentacles or lophophore arms. These arms possess a double row of smaller ciliated tentacles. The tentacles secrete mucous which is driven, along with the food particles trapped in it, to the mouth by the beating of the cilia. The mucous and the accompanying food particles are then digested.
The trunk is short and sac like rather than being long and thin, and the digestive tract is U-shaped. The animal's anus is then on the animal's back approximately opposite the animal's mouth. The truck ends in a contractile, (can lengthen or shorten) prehensile (can grip like a monkeys tail) stalk. This stalk is used for support in some species, but is joined at its farther end to a common stolon in colonial species.
Asexual reproduction by budding is common and often gives rise to colonies starting from a single individual. However sexual reproduction is the normal method of reproduction and it is similar to that in the Enteropneusts with external fertilisation. However each animal has only a single gonad and the larvae is believed not to be a tornaria, though it is poorly know.
The Pterobranchs also differ from the Enteropneusts in the possession of only one, or in some species no pharyngeal slits (Cephalodiscus sp. = 1, Rhabdopleura sp. = 0). Because these animals are generally very small there is no problem with respiration occurring simply across the body surface. Their other organ systems are similar to those of the Enteropneusts (see above).
Note:- the colours in the image at the top of this page do not represent the real colour of the animal, but are used to emphasize the different body sections.

Shailesh kr shukla

Tuesday, 24 December 2013


Roundworms (nematodes) are bilaterally symmetrical, worm-like organisms that are surrounded by a strong, flexible noncellular layer called a cuticle. Their body plan is simple. The cuticle is secreted by and covers a layer of epidermal cells. Near the body wall but under the epidermal cells are muscle cells; they run in the longitudinal direction only. A true coelom is lacking, instead, nematodes have a "pseudocoel" formed directly from the cavity of the blastula (rather than as a result of the division or folding of mesoderm). The cavity of the pseudocoel is small, being mostly filled with an intestine and oviducts or testes. A simple nervous system consists of a ring of nervous tissue around the pharynx that gives rise to dorsal and ventral nerve cords running the length of the body.
Nematodes move by contraction of the longitudinal muscles. Because their internal pressure is high, this causes the body to flex rather than flatten, and the animal moves by thrashing back and forth. No cilia or flagellae are present.
Some nematodes have specialized cells that excrete nitrogenous wastes; in others, canals or canals plus these specialized cells are present. Nematodes do not have flame cells.
Most nematodes are dioecious. Fertilization takes place when males use special copulatory spines to open the females' reproductive tracts and inject sperm into them. The sperm are unique in that they lack flagellae and move by pseudopodia, like amoebas. Development of fertilized eggs is usually direct.
Nematodes are almost unbelievably abundant. One study reported around 90,000 individual nematodes in a single rotting apple. Another reported 236 species living in a few cubic centimeters of mud. The number of described species is around 12,000, but too little attention has been paid to these animals and the true number may be closer to 500,000. Some species are generalists, occuring across wide areas and in many habitats; others are much more specialized. Nematodes have colonized nearly every conceivable habitat on earth, including such unlikely places as under beer coasters in Germany (Panagrellus redivivus). Some nematodes are also extreme habitat specialists, living, for example, only in the placentas of sperm whales (Placentonema gigantissima), or the right kidneys of minks (Dioctophyme renale)
Many nematodes are free living and play critical ecological roles as decomposers and predators on microorganisms. But nematodes also include parasitic species, a number of which affect humans directly or indirectly through their domestic animals. These include the common roundworms, which probably infest more than half the world's humans; hookworms; trichina, the worms that cause trichinosis; pinworms, another extremely common parasite, even in the United States, which can be transmitted from human to human by eggs floating in household dust; and filarial worms, primarily tropical parasites that cause diseases such as filariasis (elephantiasis) and onchocerciasis (river blindness).

Nematodes were once classified with a very large and heterogeneous cluster of animals grouped together on the basis of their overall worm-like appearance, simple structure of an internal body cavity called apseudocoelom, and the lack of features such as cilia and a well-defined head that are found in most animals. This group, variously known as Aschelminths or Pseudocoelomata, is today no longer recognized as a natural one. It is quite likely that the simple body plan of these organisms has resulted from reduction and simplification from more than one group of ancestral organisms, and so the pseudocoelom is neither a uniquely derived nor useful character. (Wallace, Ricci, & Malone 1996) The simplicity is thus a result of secondary simplification from a more complex body design, and not necessarily an indication of primitive or simple origins. Current studies indicate that nematodes are actually related to the arthropods and priapulids in a newly recognized group, the Ecdysozoa.

nematode micrographNematode cross-section
Roundworms : The image at left shows a living microscopic roundworm as viewed with an Environmental SEM. The worm is approximately one millimeter long. At right, a diagrammatic view of the internal anatomy of a roundworm, showing the simplicity of its organization. See text below for discussion. (Click on either of the pictures above for a larger image).

The body of a nematode is long and narrow, resembling a tiny thread in many cases, and this is the origin of the group's name. The word "nematode" comes from a Greek word nema that means "thread". The epidermis(skin) of a nematode is highly unusual; it is not composed of cells like other animals, but instead is a mass of cellular material and nuclei without separate membranes. This epidermis secretes a thick outer cuticle which is both tough and flexible. The cuticle is a feature shared with arthropods and other ecdysozoans. As in those other groups, the cuticle is periodically shed during the life of a nematode as it grows, usually four times before reaching the adult stage. The cuticle is the closest thing a roundworm has to a skeleton, and in fact the worm uses its cuticle as a support and leverage point for movement. Long muscles lie just underneath the epidermis. These muscles are all aligned longitudinally along the inside of the body, so the nematode can only bend its body from side to side, not crawl or lift itself. A free-swimming roundworm thus looks rather like it is thrashing about aimlessly.

Life Cycle
Steinernematids and heterorhabditids have similar life histories. The non-feeding, developmentally arrested infective juvenile seeks out insect hosts and initiates infections. When a host has been located, the nematodes penetrate into the insect body cavity, usually via natural body openings (mouth, anus, spiracles) or areas of thin cuticle. Once in the body cavity, a symbiotic bacterium (Xenorhabdusfor steinernematids, Photorhabdus for heterorhabditids) is released from the nematode gut, which multiplies rapidly and causes rapid insect death. The nematodes feed upon the bacteria and liquefying host, and mature into adults. Steinernematid infective juveniles may become males or females, where as heterorhabditids develop into self-fertilizing hermaphrodites although subsequent generations within a host produce males and females as well.
Life Cycle
The life cycle is completed in a few days, and hundreds of thousands of new infective juveniles emerge in search of fresh hosts.  Thus, entomopathogenic nematodes are a nematode-bacterium complex. The nematode may appear as little more than a biological syringe for its bacterial partner, yet the relationship between these organisms is one of classic mutualism. Nematode growth and reproduction depend upon conditions established in the host cadaver by the bacterium. The bacterium further contributes anti-immune proteins to assist the nematode in overcoming host defenses, and anti-microbials that suppress colonization of the cadaver by competing secondary invaders. Conversely, the bacterium lacks invasive powers and is dependent upon the nematode to locate and penetrate suitable hosts. 

Shailesh kr shukla