Horse hair worms

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Horse hair worms
Paragordius tricuspidatus from southern France

Paragordius tricuspidatus from southern France

Systematics
without rank: Tissue animals (Eumetazoa)
without rank: Bilateria
without rank: Primordial mouths (protostomia)
Over trunk : Molting animals (Ecdysozoa)
Trunk : String worms (Nematomorpha)
Class : Horse hair worms
Scientific name
Gordioida
Rauther , 1930
Familys

The horsehair worms (Gordioida) form one of the two classes of string worms (Nematomorpha) alongside the sea worms . They parasitize in insects in the larval stage and live freely as adults in fresh water, be it in rivers, lakes, ponds or natural and man-made temporary bodies of water.

features

The body of the horse hair worms is long and narrow in the form of a thread. Most species are between 10 and 100 centimeters long, but some species can grow up to 2 meters long. With a diameter of 1 to 3 millimeters, they are extremely thin. The color is usually brown to black. This appearance has led to the name horse hair worms, as they resemble the hair on a horse's mane or tail that fell into the water during a drink .

The horse hair worms have a skin muscle tube consisting of the cuticle , epidermis and muscles . There are only longitudinal muscles, the contractions of which allow the worms to snake. Inside the animals there is a parenchymal tissue that envelops the internal organs. The ventral longitudinal nerve cord is located within the epidermis, while the dorsal cord (present in the nectonematoida ) is receded. The cuticle formed by the epidermal cells has an areole layer, the structure of which is used to differentiate between the individual species.

distribution

The horse hair worms can be found worldwide on all continents except Antarctica. However, there is no evidence for many countries. This is probably due to the fact that there have been too few studies to determine the exact distribution of the worms. According to conservative estimates, their diversity is given as 2000 species, of which less than a sixth has so far been described.

Way of life

The horse hair worms are parasites in the larval stage. As microscopic larvae around 0.1 millimeters in length, they enter their hosts, mostly grasshoppers , crickets , praying mantises or water beetles , on whose hemolymph they feed. In their earliest stages, the larvae of many species have hooks and stiletto-like formations at their front end, with the help of which they can penetrate their host animals. Other species that have hatched in temporary waters form permanent stages when their original habitat dries out , which are then taken up by their host animals together with the plants growing there.

Another possibility for infesting a host is when the larva is first ingested by a false host, for example the larva of a mayfly , a mosquito or a mosquito . The horse hair worm cannot develop further in this organism and forms a cyst in its tissue . Only when the mayfly is eaten by a suitable host animal, such as a praying mantis, can larval development continue.

After several moults , the larvae grow to their final length. After completing their larval stage, the adults have to get into a body of water to mate and lay their eggs. Through hormonal control or dehydration, the horse hair worms influence the behavior of their host animals so that they go to the water. There the worms leave their hosts, which then usually die or drown.

During the free-living stage in the water, the horse hair worms do not ingest any food. Your pharynx , a muscular throat that follows the mouth opening, atrophies and the digestive tract shrinks.

The animals are sexually separated and show a clear sexual dimorphism . They have paired, tubular gonads that open into a sex cloak at the rear end. However , Paragordius obamai was discovered in Kenya , a species that reproduces exclusively asexually .

When mating or when several specimens live together in a small space, the worms entwine and form a tangle that has often been compared to the Gordian knot .

Systematics

There are two families in the horse hair worm class with a total of more than 320 species.

Family Chordodidae May, 1919

Family Gordiidae May, 1919

Individual evidence

  1. ^ A b Paul DN Hebert, Sidney Draggan: Nematomorpha . In: Cutler J. Cleveland (Ed.): Encyclopedia of Earth. Environmental Information Coalition, National Council for Science and the Environment, August 21, 2008 (accessed May 27, 2012)
  2. ↑ Ferda Perçin-Paçal, Serap Sancar-Baş: An Anatomical and Morphological Study about Gordius aquaticus , Linnaeus, 1758 (Nematomorpha) Found in Sarıyer, Istanbul. IUFS Journal of Biology, 67, 2, pp. 123-128, 2008
  3. ^ Andreas Schmidt-Rhaesa: The nervous system of Nectonema munidae and Gordius aquaticus , with implications for the ground pattern of the Nematomorpha. Zoomorphology, 116, 3, pp. 133-142, 1996 doi : 10.1007 / BF02526945
  4. ↑ Peter Ax : The system of Metazoa III. A textbook on phylogenetic systematics. Spektrum Akademischer Verlag, Heidelberg 2001. Chapter Nematomorpha , pp. 21–26.
  5. ^ A b George Poinar: Global diversity of hairworms (Nematomorpha: Gordiaceae) in freshwater. Freshwater Animal Diversity Assessment, Hydrobiologia, 595, 1, pp. 79-83, 2008 doi : 10.1007 / s10750-007-9112-3
  6. ^ Andreas Schmidt-Rhaesa: Morphogenesis of Paragordius varius (Nematomorpha) during the parasitic phase. Zoomorphology, 124, pp. 33-46, 2005 doi : 10.1007 / s00435-005-0109-z
  7. ↑ Ben Hanelt, Matt G. Bolek, Andreas Schmidt-Rhaesa: Going Solo: Discovery of the First Parthenogenetic Gordiid (Nematomorpha: Gordiida). PLoS ONE 7, 4, e34472, 2012 doi : 10.1371 / journal.pone.0034472

literature

  • George Poinar: Global diversity of hairworms (Nematomorpha: Gordiaceae) in freshwater. Freshwater Animal Diversity Assessment, Hydrobiologia, 595, 1, pp. 79-83, 2008 doi : 10.1007 / s10750-007-9112-3

Web links

  • Paul DN Hebert, Sidney Draggan: Nematomorpha . In: Cutler J. Cleveland (Ed.): Encyclopedia of Earth. Environmental Information Coalition, National Council for Science and the Environment, August 21, 2008 (accessed May 27, 2012)