Eight-eyed pharynx
| Eight-eyed pharynx | ||||||||||||
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Roll gel ( Erpobdella octoculata ) with cocoon |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Erpobdella octoculata | ||||||||||||
| ( Linnaeus , 1758) |
The Achtäugige Schlundegel ( Erpobdella octoculata ), even dogs flukes or Rollegel called, is a freshwater leech species from the family of Rollegel in the order of Schlundegel (Pharyngobdelliformes). This species, which occurs frequently in Central Europe, was first described by Linnaeus in 1758 and forms dense populations , especially in saprobially polluted streams.
features
The leech reaches a body length of 30 to 70 millimeters. The body is somewhat flattened and laterally keeled in the rear section, narrower towards the front end and here cylindrical. The rear suction cup is noticeably larger than the front one, and both sides are not wider than the body. On the top of the head there are eight eyes (scientific name!) In two transverse rows, these consist of a cup-like, inverted pigment spot on which the photoreceptive cells sit. Only a black point can be seen under the magnifying glass. As is typical for leeches, the body consists of segments that are secondarily divided into superficial "ringlets" (annuli). In the genus Erpobdella , each segment consists of five annuli, which, in contrast to related genera ( Dina , Trocheta ), are of the same width.
The roller gel is very variable in color from red-brown to greenish, there are both very light and very dark-colored animals ( polymorphic species). By far the most common individuals show a grid pattern of yellow pigment spots on the brown back side, which is typical of the species, and through which the roller gel can usually be distinguished from other Erpobdella species. This drawing is rarely reduced or replaced by two indistinct dark longitudinal bands (similar to Erpobdella vilnensis ). Color and drawing disappear when preserved, e.g. B. in alcohol. In case of doubt, the animals are to be determined according to the position of the sexual openings (gonopores), which in this species are located at the twelfth segment and two and a half annuli apart. The roller gel has no raised papillae on the surface (integument), but occasionally small warts.
Occurrence
The roller gel occurs in a variety of bodies of water, both flowing and standing; he is indifferent to the flow factor. It occurs in brackish water with a salt content of up to five per thousand . In large rivers it is mostly replaced by other types of throat leech, but not entirely absent.
Systematic position
The species named by Linnaeus in 1758 represents the type species of the genus Erpobdella , as it occurs very frequently in streams and rivers and was described as the first species to define the genus. Although there are numerous color and pigment variants that were once described as subspecies, E. octoculata L. 1758 is now considered a polymorphic species, characterized by numerous varieties. The reasons for the occurrence of these variants are unknown.
Ecology and evolution
Adult individuals feed on predatory by mosquito larvae ( Chironomus sp.) And sludge tube worms ( Tubifex sp.) As a whole imbibe with their muscular pharynx. Since these prey organisms can occur particularly frequently in waters polluted (eutrophicated), dense populations of up to 900 individuals / m² have been found there. The leech also sucks on larger, dead prey organisms, such as B. earthworms , water crabs or fish, whereby tissue parts are torn off and ingested. The sexual behavior of these hermaphrodites, i.e. H. Copulation via sperm injection cannulas (traumatic insemination), as well as gender conflicts regarding the male-female role, were described.
A few days after mating, the pharyngeal leeches (from April to October) produce species-specific shaped, oval, light brown cocoons from which 4 to 6 young animals hatch. The placement of the cocoons has been described several times. During the study of aquarium populations, the evolutionary biologist Ulrich Kutschera observed in the early 1980s that adult individuals who do not produce clutches suck up or suck up the emerging or freshly laid (soft) cocoons of conspecifics and thus destroy them. However, mother rules never attack their own cocoons. This intraspecific cocoon cannibalism presumably leads to density regulation of the population in well-nourished, steadily growing reproductive communities.
The species E. testacea , which is closely related to E. octoculata, lives in ponds in contrast to the Rollegel and presumably shows the same cocoon-feeding behavior that is interpreted in connection with the evolution of brood care in proboscis. In addition to the Rollegel, the Freiburg Bächle leech ( Trocheta intermedia Kutschera 2010) can also be found in southern Germany . The two types of throat leech, which can be easily distinguished on the basis of their cocoon morphology, but colonize different running waters, ie they represent spatially separated species of leech with a similar range of prey.
Individual evidence
- ↑ a b Hasko Nesemann, Eike Neubert: Annelida, Clitellata: Branchiobdellida, Acanthobdellea, Hirudinea. In: J. Schwoerbel, P. Zwick (Ed.) Freshwater fauna of Central Europe 6/2. Spectrum Academic Publishing House, Heidelberg, Berlin (1999).
- ↑ Brigitta Eiseler (2010): Taxonomy for Practice. Identification aids for macrozoobenthos (1). LANUV worksheet 14. Published by the State Office for Nature, Environment and Consumer Protection North Rhine-Westphalia. ISSN 1864-8916
- ↑ ecological information on freshwaterecology.info
- ^ Hasko Nesemann & Otto Moog: Hirudinea - leeches. In: O. Moog (Editor): Fauna Aquatica Austriaca. Catalog for the auto-ecological classification of aquatic organisms in Austria. 2nd delivery in 2002.
- ↑ a b Ulrich Kutschera: Inner-species cocoon destruction in the leech Erpobdella octoculata. Observations on aquarium cultures. Mikrokosmos (1989) 78: 237-241.
- ↑ a b Ulrich Kutschera: The feeding strategies of the leech's Erpobdella octoculata (L.): A laboratory study. Boarding school Rev. Hydrobiol. (2003) 88: 94-101.
- ↑ a b Ulrich Kutschera: | Sex-Gender-Conflicts in Aquatic hermaphrodites: are Genes Immortal? J. Marine Sci. Res. Dev. (2017) 7/2: 1-4.
- ↑ a b Ulrich Kutschera, Peter Wirtz: The evolution of parental care in freshwater leeches. Theory Biosci. (2001) 120: 115-137.