Animal Phyla

Introduction

A 1600 Work I

1600 Work II

1600 Work III

Nematomorpha

Arthropoda--Ants

Arth II--Reduviidae

Chordata--Sharks

Chordata-Sharks II

Chordata--Ratites

Mollusca--Slugs I

Mollusca--Slugs II

Nematomorpha

Bill Long 4/25/07

The "Horsehair," "Hair," or "Gordian" Worms

Online accounts of the number of species in this genera of worm range from about 230 to 320. The latter is the number in the Wikipedia article. The phylum, which means "thread form," was named in 1886 by the Estonian botanist Franz Vejdovsky. Of the 38 animal phyla listed in this article, only one, the Cycliophora, was named in the 20th century (1993). Thus, the phyla have been one of the most stable categories of the Linnaean classification system. The OED gives the following definition for nematomorph: "A member of the phylum Nematomorpha, comprising unsegmented, pseudocoelomate worms whose free-living adult forms develop from larvae that are endoparasistes of arthropod hosts."

Before unpacking some words in this definition, a few words need to be said about the "Nema" prefix. There are two other "nema"-type words used to describe phyla: Nemadota, the roundworms (ca. 80,000-1,000,000 species; you see how science is an inexact science!) and Nemertea, the ribbon worm, with about 1200 species. The latter word, however, is derived from the name of one of the Nereids (sea nymphs), Nemertes, daughter of Nereus and Doris. I would have to know more to know why.

In any case, the Greek word nema means "thread," and a slew of English words built off of it (nematoidean, nematognath, nematologist, nematophagous, nematophorous) show that it has had a useful verbal life. But one might have thought that nematology is the study of various kinds of worms, and that is partially correct, but note the OED definition: "the study of nematodes, esp. as a branch of plant pathology." Plant pathology?? Well, we have to go to a 1928 quotation to understand this: "There has arisen a distinct branch of plant pathology known as nematology, the exclusive filed of which is the investigation of plant diseases caused by eelworms. Now we understand. So I guess people in the field study both the worm and the plants.

More On the Nematomorpha

Let's return to the definition. These worms are unsegmented, in contrast to the Annelida (annelids, about 15,000 modern species), which have segmented bodies. Ok. Then, they are "pseudocoelomate" worms. This translates literally as "false gut," or "false body cavity" but the concept is, apparently, more difficult. Scholars have divided many living organisms into three categories: acoelomate (no gut at all), pseudocoelomate and eucoelomate (true guts). Most bilaterial animals, including the vertebrates, are eucoelomate while some animals, like flatworms, have no body cavity at all. The pseudocoel is actually a fully functional body cavity (between the epidermis and internal organs) but the cavity is only partially developed. I have never participated in a dissection of a Nematomorpha; so I am only reporting at this juncture what I read.

Now we move into the fun part of the definition--"whose free-living adult forms develop from larvae that are endoparasistes of arthropod hosts." The Nematomorpha are significant because of the nature of their parasitic activity. Though there is not unanimity among scholars on all the following points, here is a reasonable construction of their life's course (about a year). The female lays eggs often numbering in the millions, in gelatinous strings along the water's edge (i.e., on vegetation). Some of the eggs sink to the bottom of the water, to be eaten by fish; others seem to be eaten by grasshoppers and crickets and other arthropods who eat at water's edge. In any case, the horsehair worms [this name was derived from the observation long ago that the worms resemble horsehairs and were believed to have spontaneously generated when horses would shed hair into their watering troughs as they ate] begin to grow in their hosts. I don't know the exact process of how they take up residence, but they seem to bore into the host's body cavity and set up shop there. The horsehair worm can grow up to a yard in length, even though they are less than 3 millimeters in diameter, and they live in creatures no more than three or four inches in length. Thus, you get the picture. They tend to "take over" their host. They seem also to hinder their hosts from reproducing.

Let's pause for a moment to reflect on the human significance of this lesson. There are some creatures in the animal world who "grow to maturity" by being parasites. They suck all the food coming into the host, or a good part of it, and thus they fulfill their place in nature. Don't you know any people like this? But then, even more interesting, is that they can cause their host to "commit suicide" by apparently releasing a combination of chemicals that affect the brain of the arthropod so that it jumps into water and drowns. In other words, the parasite not only gloms onto the host but actually will not be satisfied until it has killed it. When I first learned this I thought it was weird, but here is a video clip of a cricket jumping into water and drowning and, then, the long and slitherly horsehair worm coming out of the rear end of the drowned cricket and swimming away. Watch it if you can endure! Here is an article from National Geographic Online which tells the same story, only this article uses a more charged word in its title: "Suicide Grasshoppers Brainwashed by Parasite Worms."

The name of such a worm is Spinochordodes telinii, of the Gordioida class of Nematophores. Well, after this dramatic exiting of a grasshopper or cricket, it swims away to mate, and after it mates, it dies. Thus, nearly its entire life cycle is spent drawing life from another living creature. Once it has done that it is able to reporduce and die. Born to be a parasite. Makes you think, doesn't it?

Conclusion

Most texts list two classes of Nematomorpha: Nectonematoida and Gordioida (both named in 1930). The former has but one family while the latter has two orders and five families. The Linnaean names are very similar to each other, having combinations of chords and gords and paras in the names. A handful of genera have been discovered in North America. Fortunately for us all, these slithery creatures don't take up their location in humans. That could be real trouble!

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