Potamodrilus fluviatilis
| Potamodrilus fluviatilis | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name of the family | ||||||||||||
| Potamodrilidae | ||||||||||||
| Bunke , 1967 | ||||||||||||
| Scientific name of the genus | ||||||||||||
| Potamodrilus | ||||||||||||
| Lastochkin , 1935 | ||||||||||||
| Scientific name of the species | ||||||||||||
| Potamodrilus fluviatilis | ||||||||||||
| (Lastochkin, 1935) |
Potamodrilus fluviatilis is the name of a very small, of the reason freshwater and brackish water in Europe living kind of segmented worms , at the same time so far the only kind of described family Potamodrilidae in the class of Aphanoneura is. Potamodrilus individualsfoundin North America around the year 2000are likely to belong to a second species.
features
The dorsoventrally flattened body of Potamodrilus fluviatilis is up to 1 mm long, about 100 µm wide and consists of six bristle-bearing segments and a bare front segment, from which the prostomium is clearly separated by a transverse groove. Each bristle-bearing segment has two bundles of bristles dorsolaterally and ventrolaterally, each with a long and a short bristle ( chaeta ). Sticky glands on the segments allow the animal to attach. The Coelom room is only equipped with rudimentary partitions between the segments.
Abdominal longitudinal muscles on the body wall help the animal to bend quickly, but it moves with the help of a three-lobed eyelash field on the abdominal side of the prostomium. The funnel-shaped, narrow, tail-like pygidium with its sticky glands is used to attach to the ground.
The strong pharynx has a pharyngeal pouch and a pharyngeal bulb on the ventral side of the prostomium, which however cannot be extended and is not homologated with the bulb of the archiannelida . In the second segment, the pharynx first merges into a short esophagus and then into the stomach, the 35 to 45 µm wide intestinal section that narrows between the third and fourth segments to form the 12 to 17 µm wide midgut, and the anus is almost seated at the end of the beast. The inner epithelium of the slightly curled intestine is densely covered with short cilia . The animals have 1 to 2 pairs of nephridia .
The cerebral ganglion sits in the back of the prostomium and in the anterior ring of the first segment. Similar to the Aeolosomatidae, Potamodrilus fluviatilis has two nuchal organs behind its cerebral ganglion near the ventral roots of the pharyngeal nerve ring , as they occur in most polythorns, but not in girdle worms. The two pits in front of the cerebral ganglion, on the other hand, are not nuchal organs, but other sense organs.
Similar to the Aeolosomatidae, the closed blood vessel system has a very simple structure, has no lateral vessels and essentially consists of the back and abdominal vessels, which branch off into a plexus in the region of the stomach and then reunite to form main vessels. The dorsal vessel divides at the front end of the animal into two arms, which run around the intestine as a ring and unite at the beginning of the second segment to form the abdominal vessel.
The hermaphroditic Potamodrilus fluviatilis has two pairs of testicles that discharge the sperm via paired sperm conductors into a common channel in the middle of the abdomen, as well as a pair of ovaries that open outwards through an unpaired female genital opening and at this point on the abdomen with a glandular single-layer cell layer , the so-called "pseudo-clitellum", are covered. The animals have a single unpaired receptaculum seminis , which opens out directly in front of the female sexual opening.
Potamodrilus fluviatilis only reproduces sexually, while no asexual reproduction has been demonstrated. The sex organs have so far only been described anatomically, while there are no reports for the sexual act and oviposition.
Habitat and Distribution
Potamodrilus fluviatilis is common in Europe . It has been found in particular on the bottom of large rivers, but also on the Baltic coast and in large numbers in the oligotrophic lake Stechlin in northern Brandenburg ( Germany ). Potamodrilus worms have now also been found in North America in the Roanoke River in Virginia ( United States ), but this may be a different species that has not yet been described.
Life cycle
Potamodrilus fluviatilis reproduces exclusively sexually, but the pairing of the hermaphrodites has not yet been directly observed. The "pseudo-clitellum" is used to separate a cocoon into which the eggs are laid and inseminated with the sex partner's sperm stored in the receptaculum seminis . Young animals hatch from the cocoon with a prostomium, three segments and a pygidium. At full body length with seven segments, their sexual organs mature.
nutrition
Potamodrilus fluviatilis feeds on detritus and microorganisms that adhere to the substrate and are grazed by it with the help of the muscular pharynx.
Systematics
The sister group of the Potamodrilidae is the family of the Aeolosomatidae , with which it forms the order of the Aeolosomatida and at the same time the class of Aphanoneura within the tribe of annelids .
The only species of the Potamodrilidae described so far is Potamodrilus fluviatilis, which lives in Europe . This was in 1935 by the Soviet zoologist Dmitry Alexandrovich Lastochkin first (Дмитрий Александрович Ласточкин) under the name Stephen Soni Ella fluviatilis - at that time as a kind of Aeolosomatidae family - the same time as the new genus Stephen Soni Ella described, named after the recently deceased British zoologist and specialist in Indian earthworms , John Stephenson . Due to a homonymy , however, the name Stephensoniella was replaced by the new generic name Potamodrilus in the same year and the new species name Potamodrilus fluviatilis was introduced accordingly ("river rainworm" - ancient Greek ποταμός potamós "river", δρίλος drílos "earthworm to the river ", Latin for fluviatin ) proper "). The own family Potamodrilidae was established in 1967 by the German zoologist Dieter Bunke .
literature
- Dmitry Alexandrovich Lastochkin (1935): Two new river Aeolosomatidae (Oligochaeta limicola). Annals and Magazine of Natural History, Series 10, No. 15 (90), pp. 636-645 (description of Stephensoniella gen. Nov. And Stephensoniella fluviatilis sp. N.). doi : 10.1080 / 00222933508655011
- Dmitry Alexandrovich Lastochkin (1935): New name for the genus Stephensoniella. Annals and Magazine of Natural History, Series 10, No. 16, p. 488 (allocation of the new generic name Potamodrilus ).
- Dieter Bunke (1967): On the morphology and systematics of the Aeolosomatidae Beddard 1895 and Potamodrilidae nov. fam. Oligochaeta. With 97 illustrations in the text. Zoological Yearbooks, Department for Systematics, Ecology and Geography of Animals 94, pp. 187–368.
- David L. Strayer: Ecology and distribution of hyporheic microannelids (Oligochaeta, Aphanoneura, and Polychaeta) from the eastern United States. Archives for Hydrobiology 151 (3), pp. 493-510. Stuttgart 2001.
- Günter Purschke, René Hessling (2002): Analysis of the central nervous system and sense organs in Potamodrilus fluviatilis (Annelida: Potamodrilidae). Zoologischer Anzeiger - A Journal of Comparative Zoology 241 (1), pp. 19-35. doi : 10.1078 / 0044-5231-00019 .
- Emilia Rota, Yde de Jong (2015): Fauna Europaea: Annelida - Terrestrial Oligochaeta (Enchytraeidae and Megadrili), Aphanoneura and Polychaeta. Biodiversity Data Journal 3: e5737. doi : 10.3897 / BDJ.3.e5737
- Adrian M. Pinder: Annelida: Aphanoneura. In: Catherine Mary Yule, Hoi-Sen Yong (Ed.): Freshwater Invertebrates of the Malaysian Region. Academy of Sciences Malaysia, Kuala Lumpur 2004. p. 191.
- Olav Giere: 5.14.3. Annelida incertae sedis. In: Olav Giere: Meiobenthology: The Microscopic Fauna in Aquatic Sediments. Springer Verlag, Berlin / Heidelberg 1993. pp. 134f.