Lumbriculidae

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Lumbriculidae
Lumbriculus variegatus with a double tail as a result of an injury

Lumbriculus variegatus with a double tail as a result of an injury

Systematics
Trunk : Annelids (Annelida)
Class : Belt worms (Clitellata)
Subclass : Little bristle (Oligochaeta)
Subclass : Lumbriculata
Order : Lumbriculida
Family : Lumbriculidae
Scientific name of the  subclass
Lumbriculata
Jamieson , 1988
Scientific name of the  order
Lumbriculida
Jamieson , 1988
Scientific name of the  family
Lumbriculidae
Vejdovský , 1884

The family Lumbriculidae , which forms the order Lumbriculida and the subclass Lumbriculata at the same time , is a taxon of little bristles (Oligochaeta) in the ringworm class of belt worms (Clitellata) and includes around 200 species that eat substrate in freshwater in the northern hemisphere , but also are also spread - probably through procrastination. In German they are also called glossworms , but this name refers in particular to the most famous species, the glossworm Lumbriculus variegatus .

features

The Lumbriculidae, which live exclusively in freshwater , are rather small and short compared to typical land-living Crassiclitellata (earthworms), but large compared to most aquatic little bristles. They have numerous segments and outwardly often resemble earthworms.

On each segment of the Lumbriculidae there are 4 bundles of bristles, each with 2 bristles ( Chaetae ), a total of 8 bristles, but regrowing bristles can already be visible before the old bristles fall off. Depending on the type, all of the bristles are either forked with a large lower tip and a smaller upper tip or have only a single tip; a combination of both types of bristles is very rare. The bristles are used to anchor the movement with the help of the longitudinal and circular muscles of the skin muscle tube and have a similar effect to other little bristles: If the segment is shortened by contraction of the longitudinal muscles, the bristles are extended and anchor the site of the worm; on the other hand, if the segment is lengthened by contracting the sphincter muscles, the bristles are drawn in and allow the worm to move.

The original feature of the Lumbriculidae is an extensive coelom , divided into segments by partitions , which acts as a hydroskeleton , as well as an extensive primary blood vessel system . In many species, the red blood vessels are strongly branched in each segment. The red color of the blood is due to the blood pigment erythrocruorin dissolved in the plasma , which has a very strong affinity for oxygen and enables survival under low-oxygen conditions.

Like other belt worms, the Lumbriculidae are hermaphrodites . In contrast to most of the other beltworms, which only have one or two pairs of testes and ovaries each , i.e. are octogonadal at best, their number in Lumbriculidae is 1 to 4 pairs of testes in the 6th to 10th or 9th centuries, depending on the species. to 11th segment and in 1 to 3 pairs of ovaries in the 9th to 12th segment. The male genital orifices are always in front of the female ones, and the vas deferens lead from the ciliated funnels directly in the same segment as the associated testicles to the outside. The sperm have weak connective and a short acrosome .

The Lumbriculidae have a clitellum , which consists of only one layer of cells, and large, yolk-rich eggs that fully nourish the developing embryos. In these original characteristics, the Lumbriculidae resemble the aquatic annelid worms of the families Moniligastridae and Haplotaxidae .

The nephridia are linked between the segments. The thick myofilaments have a square cross-section and an S-shape. The intestinal canal has no gizzard. In some species the foregut forms a trunk ( Proboscis off).

The segments of the Lumbriculidae easily fall apart and are able to regenerate a complete animal. In these annelid worms, asexual reproduction by breaking up into individual segments (architomy) often occurs, although there is no chain formation.

Occurrence and distribution

The approximately 200 species of Lumbriculidae are distributed in the fresh water of streams, lakes, swamps, ponds and also underground waters in the entire northern hemisphere - Eurasia and North America . Many species are highly endemic , particularly in Northern Europe , North America, and Eastern Siberia . The best-known species, the glossworm ( Lumbriculus variegatus ), which is found very often in deciduous pools in Europe, but also occurs in Australia and New Zealand , has a worldwide distribution . It seems certain that he man introduced was; its localities in Australia are concentrated on ponds in the vicinity of cities. Even to North America, where it occurs very frequently, it probably only came through humans. Another species introduced to Australia from Europe is Stylodrilus heringianus .

Life cycle

The hermaphroditic Lumbriculidae have not yet been observed during copulation, because even the very common species Lumbriculus variegatus and Stylodrilus heringianus are rarely found in a sexually mature state. It is assumed that, as with other belt worms, the sperm of the respective sex partner is absorbed into their own receptacula seminis during mating. Egg cocoons, on the other hand, have been observed in the wild: the eggs are deposited in the egg cocoons formed by the clitellum and inseminated with the sperm in the receptaculum seminis. In the cocoon, the embryos develop from the very yolk-rich eggs into small, finished worms.

Under laboratory conditions, only sexually immature animals are known, and in the wild, too, the Lumbriculidae are almost always found in this state. These are regularly divided into individual segments before sexual maturity occurs. The regenerative capacity of the Lumbriculidae is also very high for annelid worms: a whole animal can regenerate from a single segment, and this is the normal case of natural asexual reproduction in this group of animals .

Species that live in temporary bodies of water such as pools survive dry spells by forming a protective cyst around their body.

nutrition

The Lumbriculidae feed on organic detritus, bacteria and other microorganisms that they digest with the swallowed substrate - sand, silt, mud and humus at the bottom of the water. The mineral components are excreted undigested.

Genera

The more than 200 species of Lumbriculidae belong to the following genera :

literature

Web links