How many nematodes exist

Fortunately, most species of nematodes have no effect, or have a beneficial effect, on humans and their endeavours. These feed on bacteria, fungi, protozoans and even other nematodes, and play a very important role in nutrient cycling and release of nutrients for plant growth. Other nematodes attack insects, and help to control insect pests. In fact, some nematodes which attack insect pests are reared commercially and released for the control of certain insect pests as a biological insecticide.

A nematode released to control the Sirex wood wasp has been credited with saving the forestry industry up to 80 million US dollars per year in Australia. Nematodes are also important in other ways. The nematode Caenorhabditis elegans was the first multi-cellular organism to have its DNA fully sequenced.

This has led to many exciting breakthroughs in the biological and medical sciences in the last few years. This nematode is also famous in that some individuals, being carried onboard as part of an experiment, survived the Space Shuttle Columbia disaster in !

Nematodes can be found from the depths of the ocean to mountain tops. A spadeful of soil can contain more than a million nematodes! Because nematodes are so numerous and occur in so many habitats, it has been suggested that if we removed everything from our planet but nematodes, much of the topography of the Earth would still be recognisable as a film of nematodes!

The location of the various plants and animals would still be decipherable, and, had we sufficient knowledge, in many cases even their species could be determined by an examination of their erstwhile nematode parasites.

No organism on Earth is exempt. According to Colin Tudge in "The Variety of Life", it has been suggested that one of every two animal species on Earth has at least one parasitic nematode species that lives only with it.

To cite but one example, here's a vivid image by Alex Wild of a nematode-filled ant from Belize. At the other end of the spectrum, the largest known nematode is Placentonema gigantissima , which can reach around 30 feet long in the placentas of its host, sperm whales. I managed to find a purported photo of this beast ; I particularly like the fourth bullet point in its caption. And I wonder: how does this nematode get from host to host? Surely sperm whales are not like dogs, if you know what I mean, and they don't exactly have to worry about washing their hands.

In the world of plants, root-knot nematodes crawl into roots and release chemicals that swell the roots with tumors, sapping the plant's strength aboveground. At the heart of these tumors, female nematodes suck the juice from grotesque, multinucleate "giant cells". They grow fat off this rich provender, swelling in turn into their own grotesque balloons before squeezing a slimy mass of eggs from their enormous backsides.

Closer to home, the nematode diseases of hookworms, river blindness, and elephantiasis plague humans, while " worms " are major cat and dog parasites. Consider the recent shocking news that every two days, the dogs of Bristol, U. These worms can cause blindness in humans who accidentally ingest them after handling dirt.

Bad owners. Toxocara canis, the dog roundworm. I would really rather not think about what went into the creation of this photograph. Creative Commons Joel Mills. Click for license and source. Not all nematodes are parasites. Some work for their daily bread like the rest of us, foraging for food in water or soil. There are predatory nematodes who use their piercing stylets to attack and devour protists or other microbes.

See the full study here: Soil nematode abundance and functional group composition at a global scale. The reason this paper is kind of a big deal is that we show just the opposite is true. Knowing where these tiny worms live matters because nematodes play a critical role in the cycling of carbon and nutrients and heavily influence CO2 emissions. Understanding the little organisms at a global level is critical if humans are going to understand and address climate change.

For the study, researchers took 6, soil samples representing every continent, and every environment, from arctic tundra to tropical rainforest. They used microscopes to analyze the density of each type of nematode and generate a representative global dataset. Preliminary research indicates a potential for management of these nematodes in the biological control of aquatic weeds Gerber and Smart, Genera that parasitize crop plants grown in immersed culture e.

Marine Nematodes. The marine environment provides habitat for an enormous diversity of nematodes, from surface, littoral and estuarine zones to the ocean depths. One interesting group of deep sea nematodes are the Rhaptothyridae, which have no mouth and a very reduced alimentary tract.

The digestive tract is filled with symbiotic chemoaototrophic bacteria. A similar relationship exists in the mouthless genus Astomonema.

Mokievsky et al. About 4,—5, species of marine nematodes have been described and more are discovered and described from ongoing marine exploration projects. Clearly there is an enormous volume of ocean yet to be explored. Nematodes in Urban Environments. We have only begun to understand the nature of the nematode problems and the biology of nematodes in the urban environment.

As the demographics, economy, and land-use patterns in the state change, research in urban nematology will become increasingly important. Within the scope of urban nematology, are individual, societal, and commercial components. Individuals create a personal environment involving trees, shrubs, other annual and perennial ornamentals, ground covers, lawns, indoor plants, and vegetable gardens.

Frequently, the plants are placed directly into soil already containing plant-parasitic nematodes from a previous planting; nematodes may also be introduced with the current planting in associated soil and roots.

Obviously, the layout and plant species involved in urban gardening are not selected for incompatibilities of their associated nematode species. Nematodes introduced or supported by one plant species can be very damaging to neighboring or companion plants. Such individual plants have aesthetic value or generate emotional attachments and, therefore, have a high individual value.

Nematode damage to lawns and groundcover often results in poor growth, bare spots, and chlorotic appearance which the individual attempts to remedy by increasing the application of both fertilizer and water. Societal components of urban nematology include nematode effects in parks, recreation areas, landscape plantings, highways, schools, etc. Nematode problems of turf constitute an area of concern for recreational and landscape industries.

Again, all these plantings have tremendous value in terms of management input and public perception. Damage and lack of plant vigor due to nematode parasitism result in unsightly areas, increased weed competition, and increased water and fertilizer usage. Commercial components of urban nematology include the costs of nematode management-or of lack of nematode management-by producers of plants in nurseries, turf farms, and greenhouses.

The economics of urban nematology also include the activities of agrichemical industries, wholesalers, retailers, advisors and consultants. As with other areas of nematology, we should consider the positive and negative aspects of nematodes in the urban environment. Nematodes can act primarily as pests or pathogens, or can also participate in decomposer food chains by using dead organisms as sources of carbon and energy.

Often, the most productive soils contain high populations of non-parasitic nematodes participating in the cycling of minerals and nutrients. In fact, high population levels of such nematodes may be an indicator of productive soils with a healthy biological status. As knowledge of nematode problems in urban situations increases, so will the potential to design spatial patterns and sequences of backyard gardens to provide the ultimate in nematode management options.

Planting sequences and companion plantings can be selected with nematode susceptibilities, or even allelopathic effects, in mind. Enhancing the biological activity of soil to improve nutrient and moisture status, as well as the biological antagonism of nematodes, can be accomplished with minimal cost through the intensive efforts of avid gardeners in small-scale areas. The backyard garden offers the possibility of creating a microcosmic "sustainable agriculture" situation. Here is an environment that the homeowner can control and manipulate experimentally without the overriding concerns of marketability or profitability of crops.

Experimentation with soil manipulation, incorporation of organic matter, companion plants, sequences, and spatial patterns of plants may be a rich source of innovations and provide important biological insights. Biological antagonists of nematodes can be introduced and tested; beneficial nematodes for the biocontrol of insect pests can also be introduced and conserved in the system. The opportunities for observation, formulation, and testing of hypotheses are more readily provided by the backyard garden than by commercial agriculture.

To capitalize on those opportunities, many research questions must be addressed; these include plant species compatibilities in terms of host status or effects on various nematode species , and knowledge of the nematodes present at a given site and their virulence on ornamental plants.

Conceivably, increased regulation may be required for industries that impact urban nematology in order to minimize nematode introductions and spread in the urban environment. Cobb, N. North American free-living fresh-water nematodes.

Reprinted from Trans. Contributions to a Science of Nematology.