Acanthobdella peledina
| Acanthobdella peledina | ||||||||||||
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| Acanthobdella peledina | ||||||||||||
| Pit , 1850 |
Acanthobdella peledina is a fish- parasitic leech species that parasitizes salmon fish in the boreal zone . The species has scientific significance as a transitional form, which has mosaic-like characteristics of the leeches and the little bristle (scientific name: Oligochaeta), so that their relationship was unexplained for a long time.
description
Depending on the region, the animals reach a length of 19 to 32 millimeters and a diameter of 3 to 5 millimeters (rarely more), but most animals are barely 15 millimeters in length. They consist of 29 segments ( somites ). Thus each is superficially, as is typical for all leeches, subdivided into a sequence of stripes or annuli. In the species there are four annuli per thus in the middle trunk section. The sequence of somites results in a uniform curling of the worm-like body, which is flattened from top to bottom (dorsoventral) and which has an approximately spindle-shaped shape due to a slightly widened rear section. In sexually mature animals, the front of the body is curled by a sequence of two brown and two yellow annuli. Otherwise the color is extremely variable, between yellowish, gray and dark green with yellow spots. Unlike most leeches, which have a suction cup at the front and rear of the body, Acanthobdella peledina only has one suction cup, at the rear end. This consists of four somites, is relatively small and sits perpendicular to the body axis of the animal. The small mouth opening sits ventrally on the slightly separated and differentiated head. On somites four to six there is a pair of eyes on the top, so a total of six eyes. In addition, the Somite two to four each have four pairs of strong, hook-shaped bristles (setae), which are arranged in five longitudinal rows (so a total of 40 bristles). Similar to the usual suction cup, these serve to hold onto the host. The presence of such bristles is typical of annelid worms, but occurs in the leeches only in the bristle leeches, which were named after this characteristic. The scientific name also refers to it (ancient Greek ákanthos means thorn).
During reproduction, the species forms, like all girdle worms, a glandular distended "belt" region, called the clitellum, which is used to separate the egg cocoon. The genital orifices or gonopores lie ventrally in the midline of the clittelar region, the male in front of the female. The male lies in the furrow between the second and third somite, the female on the third somite of the clitellum, in the furrow between the third and fourth annulus. Like all Clitellata, the animals are pre-male (protandric) hermaphrodites. The digestive tract of the animals is relatively simple, the esophagus is hardly separated from the intestine. The caeca, typical of many blood-sucking leeches, are missing. At the end there is an anal gland whose function is unknown.
Biology and way of life
The species lives in cold lakes. Most of the animals sit on their hosts as ectoparasites . These are fish from the family of salmon fish (Salmonidae) and the closely related Coregonidae (often understood as a subfamily of these). The most important host species are trout ( Salmo trutta ), char ( Salvelinus spp.) Such as arctic char ( Salvelinus alpinus ), the white salmon subspecies Stenodus leucichthys nelma , the tugun ( Coregonus tugun ) and the arctic grayling ( Thymallus arcticus ). They can be found anywhere on the host, but preferably at the base of the dorsal fin . You hold onto there with the suction cup. The front end is anchored in the host with hooked bristles at various points to collect blood. The animals only leave the host to mate. About a week later they produce a soft, translucent cocoon that is attached to hard substrates on the bottom of the water. Later this hardens and is then colored brown. One cocoon contains 13 to 33 eggs. The young leeches hatch after about 7 months (at 4 ° C water temperature), they are then about two millimeters long. Young leeches recognize fish by the movement of the water and try to hook onto them with the bristle front end. Separated from the host, older animals also anchor themselves to the ground and make search movements with the front end, similar to fish leeches.
distribution
The species lives in northern Scandinavia, Siberia and Alaska.
Phylogeny and Systematics
The first person to describe the species, the German zoologist Adolf Eduard Grube , attributes the discovery to the natural scientist Alexander Theodor von Middendorff . The first more detailed investigation was carried out by the Russian zoologist Nikolaj Alexander Livanov in 1906.
Acanthobdella peledina, together with the species Acanthobdella livanowi (Epshtein, 1966), which is only found on Kamchatka and the Chukchi Peninsula in eastern Siberia (according to another view, placed in its own genus and then called Paracanthobdella livanowi ), the family Acanthobdellidae, the only family of the order Acanthobdellidae. Since this was discovered much later, it was long considered the only representative of the Acanthobdellida or bristle leeches. This group puzzled the systematists for a long time because some features indicated belonging to the leeches, others to the little bristles.
The main problem was the relationship to the “real” or “higher” leeches (named Hirudinida, Euhirudinea or Autobdella depending on the author) and the Branchiobdellida , another parasitic group that various authors pushed back and forth between the leeches and the little bristles has been. The relationship between these groups has not yet been clarified. According to morphological data and some results based on DNA analyzes, the bristle leeches are more closely related to the real leeches. According to other studies, they form the sister group of the real leeches and the Branchiobdellida together. Both theories have adherents to this day.
swell
- Aleksander Bielecki, Joanna Maria Cichocka, Iwona Jeleń, Piotr Światek, Bartosz Jan Płachno, Dorota Pikuła (2013): New Data About the Functional Morphology of the Chaetiferous Leech-like Annelids Acanthobdella peledina (Grube, 1851) and Paracanthobdella livanowi (196 ) (Clitellata, Acanthobdellida). Journal of Morphology 275 (5): 528-539.
- U. Kutschera & VM Epshtein (2006): Nikolaj A. Livanow (1876–1974) and the living relict Acanthobdella peledina (Annelida, Clitellata). Annals of the History and Philosophy of Biology 11 (2006): 85-98.
Individual evidence
- ↑ on the autapomorphies cf. Peter Ax: Multicellular Animals II: The Phylogenetic System of the Metazoa. Springer, 2013. ISBN 978-3662103968 . P. 69 ff.
- ↑ Roberto Marotta, Marco Ferraguti, Christer Erséus, Lena M. Gustavsson (2008): Combined-data phylogenetics and character evolution of Clitellata (Annelida) using 18S rDNA and morphology. Zoological Journal of the Linnean Society 154: 1-26. doi : 10.1111 / j.1096-3642.2008.00408.x
- ↑ Mark E. Siddall, Kathleen Apakupakul, Eugene M. Burreson, Kathryn A. Coates, Christer Erséus, Stuart R. Gelder, Mari Källersjö, Henry Trapido-Rosenthal (2001): Validating Livanow: Molecular Data Agree That Leeches, Branchiobdellidans, and Acanthobdella peledina Form a Monophyletic Group of Oligochaetes. Molecular Phylogenetics and Evolution 21 (3): 346-351. doi : 10.1006 / mpev.2001.1021