Enchytra

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Enchytra
Enchytraeus albidus from worm breeding

Enchytraeus albidus from worm breeding

Systematics
Trunk : Annelids (Annelida)
Class : Belt worms (Clitellata)
Subclass : Little bristle (Oligochaeta)
Order : Haplotaxida
Family : Enchytra
Scientific name
Enchytraeidae
Vejdovský , 1879

Enchytraeen (Enchytraeidae) are a large family of the subclass of oligochaetes . They are subordinate to the tribe of annelids (Annelida) in the class belt worms (Clitellata).

Together with woodlice , springtails and their relatives, earthworms , they are part of the most important destructors of organic matter in the soil.

features

Adult enchytrae have a body length between five and 30 mm, depending on the species. The bodies of the animals are elongated with a round cross-section. Enchytrae are hardly pigmented. Their coloration can be white, yellowish, colorless and transparent, so that their intestinal contents show through. The blood of most enchytrae is also colorless. Their relationship to earthworms is evident from the regular body segments and the presence of the belt (clitellum). The number of segments differs depending on the species and within the species. In an adult animal, the first, bristle-free segment ( peristomium ) can be followed by less than 20, but also more than 70 bristle segments . Each bristle segment is equipped with two dorsolateral (on the back) and two ventrolateral (ventral) bristle bundles made of two to six movable bristles. The belt (see chap. Reproduction) surrounds segments XII and XIII. Enchytrae are almost exclusively hermaphrodites. The male genital opening is in segment XII and the female follows directly behind it. The seed pouch is located in segment V.

The upper pharyngeal ganglion and the abdominal cord form the rope ladder nervous system .

The enchytrae have a very simply built, closed blood vessel system . A well-developed intestinal blood sinus extends around the intestine, from which the dorsal vessel branches off more or less in the area of ​​the clitellum towards the front. At the level of the upper pharyngeal ganglion, it divides into two branches, which unite under the intestine to form an abdominal vessel leading all the way back. This flows back into the intestinal blood sinus at the end of the annelid worm. In the segments in front of the clitellum there are additional connecting vessels between the abdominal and thoracic vessels. The starting point of the dorsal vessel in the area of ​​the clitellum can vary depending on the species and therefore serve to determine the species. The muscular dorsal blood vessel pulsates clearly, so that its length is clearly visible in the living, transparent enchyte. It has a heart function and thus ensures the circulation of the blood. In the genera Henlea , Achaeta and Buchholzia , the dorsal vessel in the segments near the starting point is expanded several times heart-like muscular. Depending on the type, the starting point is behind the clitellum, whereby its position can vary by 3 to 5 segments, or in exactly one segment of the clitellar region (12th to 13th segment) or in front of the clitellum. Much of the enchytra has colorless blood; in some species, especially the genus Lumbricillus , it is pale yellow or light red.

Way of life

distribution and habitat

With the exception of Antarctica, enchytrae are common worldwide. Some species were transported to large regions by international transport, so that the same species can occur in several continents today. Since the skin of the enchytrae has to be surrounded by a moist film, the animals depend on the presence of water in their habitat. Enchytrae can be found in surface waters and puddles, but also in the sea and in the sand of the seashore. The habitat of most species and individuals, however, is terrestrial: in the upper layers of moist meadow, arable and forest soils. They rarely settle deeper than 36 cm, even in dry conditions. Here they live in the water of the bottom capillary . In the topsoil there are between 5,000 and 100,000 individuals per m² on average. In English bog soils, enchytrae have the highest population density with 130,000 to 290,000 individuals per m². These mass occurrences are formed by only a few species - greater biodiversity and fewer individuals are found in weakly acidic or calcareous soils, but they can multiply strongly in areas where earthworms are only found in small numbers: in acidic soils and with heavy agricultural use . In the garden you will find a high density of enchytrae in compost heaps.

Reproduction and development

The eponymous belt (clitellum) of the belt worms only forms in sexually mature animals. This is where the penis bulbus and the egg cells mature. In addition, the glandular cells of the belt form the egg cocoon and cocoon fluid. With a few exceptions, enchytra are hermaphrodites that mutually fertilize each other. Two animals lie down ventrally against each other in opposite directions so that the fifth and twelfth segments meet. By changing the pressure of the coelom fluid, the animals evert their penis bulbus and place it in the opening of the spermathek ( receptaculum seminis ) of the partner. This is where the sperm is stored until fertilization, which takes place outside the body. After copulation, the penis is drawn in again by superficial muscles. Since enchytrae are bilaterally organized, all genital organs are present in pairs in the same segment.

Several days can pass before the eggs are laid. During this time, the cocoon shell is formed by the belt and one or more egg cells rich in yolk are introduced. The clitellum is now significantly thickened. If the cocoon is prepared for fertilization, the enchytrae creeps through with peristaltic movements "backwards" like through a hoop until the cocoon comes to lie at the level of the sperm opening. Now the stored sperm gets inside the egg cocoon, whereupon the animal completely withdraws from it towards the front end. The two openings of the cocoon "ripen" close immediately, so that it takes on the typical lemon shape of the egg cocoon. Finally, the enchytrae covers the egg cocoon with earth particles. It is believed that this treatment is supposed to keep the cocoon from drying out. During the period of their greatest fertility, enchytres deposit an egg cocoon almost every day. At 21 ° C it takes about nine days for the young to hatch. After another eight days, the enchytra are sexually mature. Immediately after hatching, enchytrae have only 17 to 21 segments and grow at least until the onset of sexual maturity. The life expectancy of enchytrae under laboratory conditions is approx. 100 days to over a year, depending on the species.

Asexual reproduction takes place in a few species of enchytrae . Enchytraeus fragmentosus manages without genital organs and girdles and, according to current knowledge, reproduces exclusively asexually: the adult animal breaks up into pieces of mostly five segments. These develop into a full animal within 10 days.

nutrition

Enchytra feed mainly saprophagous . With their mouth pores they ingest rotting material, mostly of plant origin ( detritus ), together with the microflora adhering to it - bacteria, fungi and protozoa. Unlike earthworms, terrestrial enchytrae avoid the mineral soil components, so they do not contribute to the formation of clay-humus complexes , but rather produce mold humus .

The throat of the enchytrae can be turned out. To take in food, it is pressed onto food particles that stick to it and then drawn in again.

Importance to humans

  • Humus and compost formers: Due to their decomposing diet, enchytrae make an important contribution to humus formation and thus to maintaining soil fertility in more acidic locations.
  • Aquaristic : breeding of enchytrae - especially Enchytraeus albidus - as valuable live food for ornamental fish; mainly species living on the ground ( catfish , loaches ). Because of the high nutrient content, however, enchytrae should not be the main food of the fish.
  • Bioindicators : In the “Enchytrae Test” according to Westheide and Bethke-Beilfuss, the animals are used as test organisms for environmental toxins.
  • Pests: In the absence of more suitable food sources, enchytrae damage the fine roots of potted plants.

Systematics

At least 650 species have been described worldwide; 200 to 300 occur in Central Europe. Often their physique differs so slightly that an exact determination only microscopically z. B. can be carried out using the sperm. As a result, there are taxonomic uncertainties, so that species are possibly described several times under different synonyms or individuals were assigned to another, very similar species.

Genera and species (selection)

literature

  • Gerhard Hartwich: Family Enchytrae . In: Urania animal kingdom. Invertebrates 2. Urania-Verlag Berlin in Dornier Medienholding GmbH, Berlin 2000.
  • Wilfried Westheide and Monika C. Müller: Organization and reproduction of Enchytraeen (Oligochaeta). . Publications on scientific films, Biologie 22, pp. 153–170 (FILM C 182 1). IWF Institute for Scientific Film, Göttingen 1995.
  • Wilfried Westheide and Reinhard Rieger (eds.): Special zoology. Part 1: Protozoa and invertebrates. 2nd edition, Spektrum, Elsevier GmbH, Munich 2007.
  • Christian Overgaard Nielsen, Bent Christensen: The Enchytraeidae - critical revision and taxonomy of European species. Naturhistorisk Museum, Aarhus 1959.

Web links

Commons : Enchytraeidae  - Collection of images, videos and audio files