Crab gel

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Crab gel
Branchiobdelliden on the scissors of a signal crab (Pacifastacus leniusculus)

Branchiobdelliden on the scissors of a signal crab ( Pacifastacus leniusculus )

Systematics
Empire : Animals (Animalia)
Trunk : Annelids (Anellida)
Class : Belt worms (Clitellata)
Subclass : Leeches (Hirudinea)
Order : Crab gel
Scientific name
Branchiobdellida
Holt , 1965

The crab leeches or gill leeches (Branchiobdellida) are an order of leeches (Hirudinea) with about 150 species that live as commensals or symbionts , in a few cases as parasites on the gills or other parts of the body of freshwater crabs . They show characteristics of both leeches and little bristles and are only common in freshwater in the northern hemisphere.

features

The approximately 150 species of crab leeches reach maximum lengths of 0.8 to 12 mm. The crab leeches have a fixed number of 15 segments, the first ten of which have an outer ring. The first four segments form the head, which lacks a prostomium, while 11 segments form the trunk. The crab leeches have a fully developed coelom which , like the little bristles, has segmental septa in the area of ​​the trunk . There is also a simply constructed primary closed blood vessel system. As with all leeches with the exception of the bristle leeches, there are no bristles ( chaetae ), while there is a rear suction cup formed by the last segment as well as a front suction cup . The foregut of the cancer leeches is designed as a muscular throat with two jaws, while the following intestinal sections do not have strong muscles and the intestinal canal does not expand. The animals are hermaphrodites with two pairs of testicles , a penis and a receptaculum seminis .

Occurrence, habitat and species examples

The crab leeches are common in inland waters of Europe , Asia , North America and Central America . Most species live as commensals on the gills or other parts of the body of freshwater crabs, where they graze on microscopic algae and small animals. However, some species are parasites .

On the domestic European crayfish , especially the noble crayfish ( Astacus astacus ), there are four species that attach their egg sacs at the host by their mutual mating. The best researched is the great crab leech ( Branchiobdella parasita ), which is up to 1.2 cm long and lives as a commensal, especially on the carapace and abdomen of crabs. Also commensals on crayfish are the little 4.5 mm long small crab leech ( Branchiobdella pentadonta ) and the roughly equally large Balkan crab leech Branchiobdella balcanica , both of which can often be found on crab claws . Branchiobdella hexadonta , which is only about 3 mm in size, lives in the gill cavity of crayfish and is a facultative parasite that occasionally feeds on the host's gill tissue . The cancer gels are host specific and do not spread to other cancers. Branchiobdella astaci and Branchiobdella balcanica are therefore considered to be almost extinct due to the displacement of the noble crabs and Galician crayfish by the crayfish plague and invasive cancers . Xironogiton instabilis live on signal crabs ( Pacifastacus leniusculus ) and Cambarincola mesochorus on red American marsh crayfish ( Procambarus clarkii ) as commensals of crustaceans introduced to Europe .

Branchiobdella parasita and probably other species eat as predators and midge larvae , water fleas and copepods . Since the crab leeches clean the crustacean shell, Hasko Nesemann characterizes the relationship of the crab leech to cancer not as commensalism, but as a symbiosis .

Systematics

Since the Krebsegel both features of leeches and the oligochaetes have their systematic position has long been controversial. The Branchiobdellidae family (at that time still as Branchiobdellea without the ending -idae, which was later prescribed for families) was listed in 1851 by Adolph Eduard Grube in his work The Families of the Annelids with details of their genera and species , where he placed them with the leeches. The synonyms Bdellodrillidae, Discodrillidae, Discodrilidae (Vejdovsky, 1884) and Drillobdellidae were later used as names deviating from this for one and the same family. Maurice C. Hall raised the group in 1914 to the status of a superfamily Branchiobdelloidea within the Wenigborster. In 1965 Perry C. Holt set up his own Branchiobdellida order. In 1999, Peter Ax names the autapomorphism of the monophyletic group Branchiobdellida as the reduction of the segments to 15 and the absence of a prostomium, the reduction of the nephridia to two pairs, the two jaws as a convergent development to the jaw rules and the absence of bristles as a convergence to the bristle flukes .

The Branchiobdellida comprise the following five families :

literature

  • Hasko Nesemann: Crayfish and crayfish leech (Annelida: Branchiobdellida) - a symbiosis. In: Stapfia. Volume 58, Linz 1998, also catalogs of Upper Austria. State Museum. New episode no. 137, pp. 197-204, PDF on ZOBODAT
  • Peter Ax : The system of Metazoa II. A textbook on phylogenetic systematics. Gustav Fischer Verlag, Stuttgart / Jena 1999. Chapter Hirudinea , pp. 65–73.
  • Adolph Eduard Grube : The families of the Annelids with details of their genera and species. Verlag der Nicolaischen Buchhandlung, Berlin 1851. S. 114f., XXV. Branchiobdellea family.
  • Perry C. Holt (1965): The Systematic Position of the Branchiobdellidae (Annelida: Clitellata). Systematic Zoology 14 (1), pp. 25-32.
  • SR Gelder (1996): A review of the taxonomic nomenclature and a checklist of the species of the Branchiobdellae (Annelida: Clitellata). Proceedings of the Biological Society of Washington 109 (4), pp. 653-663. Archive link, Carnegie Museum of Natural History ( October 15, 2011 memento in the Internet Archive ).
  • Hasko Nesemann, Eike Neubert: Annelida, Clitellata: Branchiobdellida, Acanthobdellea, Hirudinea. Spectrum Akademischer Verlag, Heidelberg / Berlin 1999. pp. 6-9. Class Branchiobdellida.
  • Urania Tierreich , Volume 2. Urania-Verlag, Leipzig / Jena / Berlin 1966. P. 70, Family Branchiobdellidae, Krebsegel .
  • Maurice C. Hall (1914): Descriptions of a New Genus and Species of the Discodrilid Worms. Proceedings of the United States National Museum 48 (2071), pp. 187-193.

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