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General Information Nematomorphs What are Nematomorphs? Gordiids Who was Gordius? Life cycle Nectonematids Pets and humans Where to find worms Diversity Why study these worms? |
General Information -> Nematomorphs What are Nematomorphs? Nematomorphs are a group (phylum) of
parasites. They are long and
thin worms (up to several meters (yards) long) and grow to this size
within their hosts. The
Nematomorpha consists of two groups (classes).
The
nectonematids
are parasites of marine crustaceans such as crabs and
shrimp. The gordiids are usually
parasites of terrestrial arthropods such as crickets, grasshoppers,
beetles,
mantids and cockroaches. Based
on
molecular evidence, the phylum Nematomorpha has been shown to be the
sister
group to Nematodes. Fossil gordiids have been found emerging from a cockroach trapped in fossilized amber dated at 15-45 million years ago. However, it has been suggested that this group might date back to the Carboniferous. Compared with most animal phyla is a relatively understudied metazoan phylum. Although nematomorphs make up only 1 of 3 animal phyla specializing solely on a parasitic life style, little attention has been focused on this enigmatic group scientifically.
Freshwater nematomorphs are known as gordiids. They are also known as Gordian worms, wire worms, horsehair worms, and water snakes. In German, they are commonly referred to as "Saitenwurm" or violin string worm. Adult worms. Each worm roughly measured 25 inches. Why are they called Gordian Worms? According to legend, during the fourth century, a Phrygian farmer named Gordius was chosen as an oracle and was given a small kingdom to rule. In gratitude to the Olympian Gods, Gordius hung one of his plows in the temple of Jupiter with a knot so cunning it could not be untied. The oracles predicted that whoever untied the plow would become ruler of Asia. All who made an attempt at the knot failed. Years passed, before a man named Alexander solved the puzzle by taking his sword and with one confident stroke loosened the plow. This hero was duly honored with the prize as well as the title Alexander the Great.
Larva of Paragordius varius.
Scale bar indicates 10 microns. To see more larvae, click here.
Larvae are heavy, cannot swim and will stay at the bottom of the water column, and will thus look for hosts in the bottom of rivers and streams. Gordiid larvae will now have to find a way to get into the body of the cricket. Crickets are not found in the same environment as the gordiid larvae, so the larvae must use a transport host, in order to be transported to the cricket. Gordiid larvae do this by inching along the bottom of the stream or lake, and sooner or later will be ingested (swallowed) by another animal. Once the gordiid larvae are inside most any aquatic animal, they encyst.
Cyst of Paragordius
varius.
Note the thick cyst wall surrounding the larva.
This cyst was formed in a freshwater snail. To see more cysts, click here. As a final act, worms manipulate the behavior of the cricket, and it commits 'suicide' by jumping into water. Once the worms sense the presence of liquid (water in this case) they start actively exiting the host. A process which can take a few seconds to a few minutes. To watch a video of this process, click here. Adults of Paragordius
varius exiting a
cricket host.
The cricket was infected with cysts 28 days prior. Below is a summary of the typical Hairworm life cycle. Typical
gordiid life cycle; transition from aquatic environment to definitive
host
Nectonematidsachieved by cyst surviving the metamorphosis of aquatic insects (indicated by dashed arrow). To learn more about this parasite life cycle, read the scientific papers describing their discovery by clicking here and here. A stated above, the nectonematids are parasites of marine crustaceans such as crabs and shrimp. These worms are very rarely seen, and only a few dozen reports exist, documenting them. All nectonematids fall in the genus Nectonema. The marine genus Nectonema
is known from several locations worldwide (including the
Northern
Atlantic, the Mediterranean, Indonesia, and Japan), with the
latest report being from New Zealand. With two exceptions, reports are
usually made of single worms. The exceptions have been from
the
Bay of Fundy and some fjords in Norway. In most cases,
Nectonema
was found inside its hosts and rarely free-living. |
© Copyright 2014 Ben Hanelt, Matt Bolek, and Andreas Schmidt-Rhaesa Updated: July 2015 |