Well digger worm

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Well digger worm
Systematics
Subclass : Diplotesticulata
Superordinate : Metagynophora
Order : Haplotaxida
Family : Well worms (Haplotaxidae)
Genre : Haplotaxis
Type : Well digger worm
Scientific name
Haplotaxis gordioides
( GL Hartmann , 1821)

The well grave or well grave worm ( Haplotaxis gordioides ) is a ringworm - species from the family of well worms (Haplotaxidae) in the class of belt worms (Clitellata), which is distributed as a cosmopolitan in groundwater and spring waters and feeds on smaller annelid worms. It is also called " well wire worm", but this is also a name for the externally very similar, phylogenetically but in no way closely related as well as anatomically and lifestyle completely different water calf .

features

The pink to dark red well burial worm is noticeably thin and long with only about 1 mm, at most 1.15 mm thick and a considerable length of 15 cm to 20 cm, sometimes even up to 40 cm, which gives it a thread-like (filiform or nematomorphic) shape . The annelid worm has around 200 to 480 segments , but these cannot be seen with the naked eye, only under a magnifying glass. This has repeatedly led to the fact that the well burial worm was confused with string worms (Nematomorpha) such as the water calf.

On the belly side of the well digger worm, there are two individual, strong, sickle-shaped bristles ( Chaetae or Setae) on each segment , with which the conspicuously agile animals anchor themselves in the ground and provide the necessary support for the locomotion made possible by the longitudinal and circular muscles of the skin muscle tube . The abdominal bristles are provided with bristle glands on the 12th, 13th and 14th segments. On the back there are two individual small and straight bristles per segment, which are missing on the front segments and sometimes even on the entire wellworm. In young worms, the bristles are significantly thinner and more curved than in adult worms.

The prostomium (mouth segment) of Haplotaxis gordioides is elongated and often set off by an annular groove, which is why it is also known as prolobate or zygolobate. The peristomium , on the other hand, is very short. The 5th to 18th segments each have two stripes, the front one being shorter.

In the area of ​​the esophagus, Haplotaxis gordioides has a muscular stomach which is enlarged in three places and which occupies four to six segments and is provided with circular muscles in its wall. The blood vessel system is well developed, although capillaries are absent. The abdominal and dorsal vessels are connected to each other and to the intestinal blood sinus in each segment with a strong, contractile ring vessel. Like all belt worms, the well digger worm is a hybrid , and like most well worms it is octagonal: it has two pairs of testicles in the 10th and 11th segment and two pairs of ovaries in the 12th and 13th segment. In the 11th and 12th segment, the short paired vas deferens lead to the outside via a pair of male genital openings, with no penile bristles or penises. The female genital orifices are located in the 13th and 14th segment, i.e. behind the male openings. There are two unpaired sperm sacs between the segmental septum 10/11 and the 12th segment or the segmental septum 11/12 and the 18th segment, as well as an unpaired egg sac that extends to the 19th segment. The animal has three pairs of receptacula seminis located in the 7th, 8th and 9th segments. The ring-shaped clitellum , made up of a layer of cells, extends from the 10th to the 13th segment, and the copulatory glands are located from the 11th to the 14th segment.

distribution and habitat

The well digger worm is widespread worldwide and is considered a cosmopolitan , but is only found scattered due to its rather hidden habitat. There are many localities, especially in Europe and North America.

Haplotaxis gordioides is considered a stenothermic species that can be found in cold water. It inhabits sandy and silty subsoil in springs , wells , streams, rivers and lakes, where it was found at depths of over 300 m.

nutrition

The well burrower worms primarily prey on other small annelid worms, including Tubifex or smaller well worms, which they suck in as a whole with the help of their muscular pharynx.

Development cycle

Well burrowing worms are hermaphrodites, but have to mate to reproduce. During copulation, two animals wrap their front ends around one another on the abdomen and exchange sperm, which enter the receptaculum seminis of the sex partner. A secretion from the clitellum forms an egg cocoon into which the wellworm first releases its own eggs and then the sperm of its sex partner from its receptacula seminis, thus enabling fertilization in the cocoon. Here the embryos develop into finished small worms.

Systematics

The Swiss zoologist GL Hartmann found a well worm in his well in 1800, which he thought at first glance to be a water calf, but he soon noticed the curling and bristles under a magnifying glass. In 1819 he gave a lecture on this to Swiss scholars and published his first description in 1821 under the German name “ Nematode-like earthworm”, scientifically Lumbricus gordioides , the specific epithet referring to the generic name of the water calf Gordius . The genus name Haplotaxis goes back to the German zoologist Werner Friedrich Hoffmeister , who in 1843 described a specimen of the species under a different name, Haplotaxis menkeana , and at the same time established the genus. Since the name Haplotaxis was at times a recognized generic plant name, this was avoided even among zoologists and therefore the species was named with the synonym Phreoryctes menkeanus for a long time .

literature

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