Criodrilus lacuum

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Criodrilus lacuum
External genital organs of Criodrilus lacuum. Drawing from Barrie GM Jamieson (2006): Non-leech Clitellata.

External genital organs of Criodrilus lacuum . Drawing from Barrie GM Jamieson (2006): Non-leech Clitellata.

Systematics
Class : Belt worms (Clitellata)
Subclass : Little bristle (Oligochaeta)
Order : Earthworms in the broader sense (Crassiclitellata)
Family : Criodrilidae
Genre : Criodrilus
Type : Criodrilus lacuum
Scientific name of the  genus
Criodrilus
Hoffmeister , 1845
Scientific name of the  species
Criodrilus lacuum
Hoffmeister , 1845

Criodrilus lacuum is the name of the mud in freshwater encountered oligochaetes - kind from the family of Criodrilidae in order Crassiclitellata (earthworms in the broader sense), which in the 19th century, first by finds in Lake Tegel in Berlin and then in the Danube in Austria got known. Due to similar finds in Europe , the Middle East and North Africa , the species described have now been synonymous with this species, so that the genus Criodrilus is currently regarded as monotypical .

features

Criodrilus lacuum has a rectangular body from the 9th segment, flattened at the front and narrowed at the back, which at rest is 4 to 10 mm wide, usually about 5 to 8 cm or 15 cm, in the largest individuals about 20 to 30 cm long and can have more than 200, sometimes over 300 segments, but is able to stretch to about twice the length. It is very soft and fragile and quickly sheds its tail end, which grows back again. Regenerated tails have a fresh red color and are thinner than old ones. Outwardly , Criodrilus lacuum resembles the well-known earthworms of the Lumbricidae family, but differs from them by its narrow tail. The animals have a rusty yellow, red or reddish to brownish color, which turns gray or brown on the back, in some individuals into blackish color, while the area of ​​the vulva at the female genital openings on the 14th segment is yellow.

The head flap ( prostomium ) of Criodrilus lacuum is very elongated and almost as long as the mouth segment. It is zygolobic, so it rests on the mouth segment without a dorsal process. On the four edges of the body, on each segment, there are four bundles of bristles, each made of two individual, slightly curly bristles with a rough end hook.

In the rather high hypodermis, the longitudinal muscle bundles arranged in “boxes” are developed as a thick layer. Two thick nerve branches extend forward from the pair of upper pharynx. The mouth leads into an initially narrow and then sack-shaped enlarged pharynx , which is followed by a narrow esophagus in the fourth segment . In contrast to earthworms, there are no goiters, muscles or gizzards. The long midgut, which completely lacks a typhlosolis, only merges at the very back into a short rectum, which leads outwards in an anus located on the back.

The closed blood vessel system consists of 3 large longitudinal vessels - the back, abdominal and neural vessels - and these connecting side vessels, of which there are 2 pairs in the middle and back segments in each segment, which branch out into capillaries, thus supplying the organs and enable gas exchange with the surrounding water in the skin. In the 7th, 8th, 9th, 10th and 11th segments, however, the lateral vessels are designed as pulsating lateral hearts. According to František Vejdovský , the dorsal vessel, which he still calls the “heart”, develops in the new segments at the rear end of the annelid from a double system by merging two vessels.

The well-developed, large nephridia open out via an indistinct end vesicle in front of the ventral bristle bundles, but are absent in the anterior segments. The coelom fluid contains numerous, round to star-shaped amoebocytes .

Although the Erstbeschreiber Werner Friedrich Hoffmeister took his worms no belt, has Criodrilus lacuum as Crassiclitellat a multilayer annular clitellum , that's front and rear limited only dimly and about up to 45 segment ranges from 16. The hermaphrodite has a pair of female genital orifices on the abdomen on the rear edge of the 14th segment and shortly behind it on the 15th segment a pair of male genital orifices that sit further out on porophores. On the other hand, there are no openings in the receptacula seminis.

Habitat and way of life

Criodrilus lacuum can be found in the mud of inland waterways such as lakes and slow-flowing rivers , where it lazily burrows through the ground. It stays close to its surface, holding the heavily perfused tail part, which is densely pervaded with capillaries, mostly on the surface of the ground into the open water, in order to be able to absorb oxygen and release carbon dioxide from it. He can not swim. It can be kept alive for a long time in clean water.

Like other Crassiclitellates , Criodrilus lacuum is a substrate eater that digests the organic components of the swallowed substrate as well as the microorganisms it contains. In the poorly muscular intestines of individuals from Lake Tegel, Hoffmeister found gray mud and small root fibers.

Development cycle

Like all girdle worms , Criodrilus lacuum is a hermaphrodite and forms 1 to 3 pairs of up to about 5 mm long, spirally wound pseudospermatophores , which the first writer Hoffmeister calls - according to Vejdovský, obsolete, i.e. can only be used once - " penes " and from the beginning of July at can be seen in all adult specimens. They stand in front of or next to the female sex openings. If there are 2 pairs, one is below and the other above them. A single pair is usually above the opening. During copulation, each of the two copulating individuals attaches its pseudospermatophores to the sex partner and thus ensures the exchange of sperm.

The elongated, spindle-shaped egg cocoons with their elongated ends between 4 cm and 5 cm long were found in very large numbers at the bottom of Lake Tegel in 1845 and have been described as larger than any other annelid worm. They are twisted and curved or straight and thickest in the middle. Their skin is thicker than other Crassiclitellates, light yellow or grayish yellow. At one end the extension of the bowl is compressed into a short plate, at the other end it is drawn out into a long thread that is used to attach it to aquatic plants. The clutches were found in large bundles on the roots of the aquatic plants standing on the shallow shore of Lake Tegel, especially Sagittaria and Nymphaea , while the worms themselves were only found some distance from the shore. Even if each cocoon contains more than 30 eggs, in spite of the considerable size of the cocoons, usually only 3 to 6 embryos develop in each, i.e. not more than, say, in the case of a thawworm , but sometimes 20 embryos. These eventually turn into fully developed small annelids that turn brown when hatched.

distribution

The Tegeler See - first place where Criodrilus lacuum was found
Old Danube near Vienna - another place where Criodrilus lacuum was found

The Tegeler See near the then Prussian metropolis of Berlin is the first place where the species Criodrilus lacuum was found , where the animals and their egg cocoons were found in large numbers in the mud by the student Fritz Müller in 1845, only to be described as a new species shortly afterwards by Werner Friedrich Hoffmeister become. Another multiple find followed in 1876 by Berthold Hatschek , who found the animals in the backwaters of the Danube near Linz and in 1877 sent some individuals including empty cocoon shells to Vejdovský in Prague. The latter identified the animals as belonging to the same species. In 1912 Viktor Janda also mentions oxbow lakes of the Danube near Vienna and Klosterneuburg .

In 2006, RJ Blakemore names Europe ( Italy , Hungary , Austria , Germany , France , Spain , Portugal , former Yugoslavia , Greece , Latvia , Poland , Russia ) as well as Turkey ( Asia Minor ), Tunisia , Algeria , Syria , Lebanon and Israel or Palestine . In addition, occurrences of Criodrilus lacuum in planters in Baltimore ( USA ) and in rice fields in Rio Grande do Sul ( Brazil ) have been reported, which may be due to introduction.

System of the genus and species

Werner Friedrich Hoffmeister described in 1845 at the same genus Criodrilus ( "Aries earthworm", ancient Greek κριός Krios , "Aries" δρίλος, δρῖλος drílos, drîlos "earthworm") and the type Criodrilus lacuum ( "Aries earthworm of Lakes" Latin lacus , "Lake", lacuum "the lakes"). He initially placed the species as an earthworm to the Lumbricidae , and later it was counted among other things to the Glossoscolecidae or the Almidae . In 1884 František Vejdovský finally established the initially monotypical family Criodrilidae .

John Stephenson described annelworms from Lake Biwa, Japan, as Criodrilus bathybates in 1917 . Barrie GM Jamieson granted this species its own genus and named it Biwadrilus bathybates , which he also placed in a separate family Biwadrilidae .

The following species, among others, were later described in the genus Criodrilus :

  • Criodrilus miyashitai Nagase & Nomura, 1937
  • Criodrilus ochridensis Georgevitch, 1950
  • Criodrilus aidae Righi, 1994
  • Criodrilus venezuelanus Righi & Molina, 1994

While the Criodrilus miyashitai found in Japan is a synonym Biwadrilus bathybates , the other Criodrilus species as well as some species listed under other generic names have been synonymous with Criodrilus lacuum on the basis of a work by RJ Blakemore from 2006 , so that Criodrilus is a monotypical one Genus acts. At the same time Biwadrilus bathybates was placed back in the family Criodrilidae.

literature