Roundworms, also known as nematodes (and sometimes incorrectly spelled “round worms”), are one of the most diverse animals in the world. Over 28,000 roundworm species have been discovered, well over half of which are parasitic. The present accounting of roundworms is no where near complete, however, as it has been estimated that there are over 1,000,000 species of roundworms on the planet. That is 1,000,000 different species of roundworms, not just the number, of course, of roundworms on the planet in general, which is surely larger by several orders of magnitude. Some people confuse roundworms, and ringworm, probably because ’round’ and ‘ring’ seem similar, however ringworm, which is not actually a worm at all, is something completely different.
With such a staggering number of different species of roundworms, it is not surprising that the various kinds are often hard to distinguish from one another. (Imagine trying to conceptualize a million different animals that are sufficiently similar to part of the same phylum, yet different enough to be classified as a separate species.) Presumably, the similarities between species makes the process of cataloging all the different roundworms, a truly monumental undertaking, all the more challenging.
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Given their diversity, roundworms have adapted to almost all ecosystems. You can find roundworms in a tropical ocean, a desert, the arctic, and everywhere in between, including high and low elevations. They are omnipresent in bodies of water, where their count often far outnumbers any other animal present. As a case in point, roundworms account for 90% of all life forms found on the ocean floor.
Roundworms tend to be small, with lengths under 2.5 millimeters, and this makes sense – if they were significantly larger, the astronomical number of worms would cover the entire world. Even the largest roundworms are customarily only about five centimeters long, although some of the parasitic species sometimes grow a little longer. The smallest species, in contrast, are microscopic. Although their appearances vary widely, roundworms often have distinctive features like rings or ridges around their bodies.
Although thousands of species of roundworms live in nature performing vital ecological roles, like the recycling of certain nutrients in ocean environments, many people think of roundworms as parasites, and rightfully so. Roundworms are responsible for causing all sorts of problems with pets, especially cats and dogs, whose small intestines serve as an inviting habitat to certain types of roundworms. Moreover, once a pet is infected, it can spread the worms to the other pets around it, chiefly because roundworms may produce millions of eggs a day that can be passed into the environment.
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Humans can also be afflicted with roundworms, normally by way of ingesting infective eggs. If infected, the larvae can travel through a person’s tissues, like his or her liver or brain, which can cause inflammation or mechanical damage to organs. Roundworms can even cause blindness when their larvae migrate through a person’s eyes, a tragedy to which children are more susceptible than are adults.
Roundworms are all over the world in prodigious numbers. Some are parasitic, causing problems to their hosts, others play a key part in their habitat, helping maintain the health of the environment. Since a million different species of roundworms are believed to exist, this is hardly surprising.