Aphanoneura
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| Vejdovský , 1884 |
Aphanoneura the name of is class very small, mainly in freshwater living annelids . It comprises two families : the Aeolosomatidae with around 30 species and the monotypical family Potamodrilidae with the only described species Potamodrilus fluviatilis .
features
The aphanoneura are about 0.3 to 10 mm long and about 0.04 to 0.06 mm wide. They have a continuous coelom and 6 to 20 bristle-bearing segments that are not separated from one another by partitions inside. There is a pair of nephridia in each of the anterior segments . The closed blood vessel system is very simple and consists only of an abdominal vessel and a pulsating dorsal vessel in the front section of the animal that is connected to it by a ring and is located under the peritoneum of the intestine and branches around the intestine behind the esophagus or merges into an intestinal blood sinus . The blood is colorless. The intestine, which is lashed throughout, is divided into a muscular pharynx , a narrow esophagus and a broad midgut, which gradually tapers towards the rectum. The very simple nervous system consists of an upper pharyngeal ganglion and a barely visible nerve cord that runs along the abdominal epidermis. Similar to the many bristles , the animals also have nuchal organs .
The Aphanoneura are hermaphrodites that exchange their sperm when mating and lay their eggs in cocoons. While the sperm are formed by testicular cells in several segments and released through several paired sperm conductors, the egg cells are created in only one segment with ovaries and are released through an unpaired female pore. A glandular epithelium (“pseudo-clitellum”) made of a layer of cells, which is used to separate the egg cocoon, is located here on the abdomen. The sperm of the sex partner is stored in paired or unpaired receptaculum seminis until the eggs are fertilized . While the Aeolosomatidae reproduce mainly asexually by architomy, the Potamodrilidae only reproduce sexually.
The animals feed on microorganisms and detritus, which are either sucked in by the substrate or ingested with the substrate and digested inside.
Occurrence and distribution
The Aeolosomatidae live in or on the sediment of fresh water and brackish water , a species in salt water . They are common worldwide.
Systematics
In 1828 , Christian Gottfried Ehrenberg described Aeolosoma hemprichi as the first species of the Annelids that are now part of the Aphanoneura , which he named after the Silesian zoologist Friedrich Wilhelm Hemprich , who died shortly before at the age of 29 . The generic name means "nimble body" ( ancient Greek αἰόλος aiólos "nimble", σῶμα sō̂ma "body"). The English zoologist Frank Evers Beddard described the family Aeolosomatidae with the only genus Aeolosoma in 1895 as small "freshwater oligochaetes " whose segments are not characterized by regular partitions and whose prostomium is ventrally covered with eyelashes. The taxon Aphanoneura was created in 1884 by the Bohemian zoologist František Vejdovský , who named the animals after their hidden nervous system ( ancient Greek ἀφανής aphanḗs "invisible", νεῦρον neûron "nerve"). At that time only types of Aeolosomatidae family were known as Potamodrilus fluviatilis until 1935 by the Soviet zoologist Dmitry Alexandrovich Lastochkin (Дмитрий Александрович Ласточкин) is still the only kind of family Potamodrilidae described - first under the name Stephen Soni Ella fluviatilis (after the English zoologist John Stephenson ), due to a homonymy, however, already in the same year with the new generic name Potamodrilus ("river rainworm" - ποταμός "river", δρίλος "earthworm", Latin fluviatilis "belonging to the river").
Both the Aeolosomatidae and the Potamodrilidae are hermaphrodites, form a “pseudo- clitellum ” in the area of the ovaries and lay their eggs in a cocoon, without any parapodia . That is why they were counted among the little bristles (oligochaeta) for a long time . They were viewed either as a particularly primitive or as a secondary simplified group. On the other hand, the animals have nuchal organs , which, like the position of the cerebral ganglion in the prostomium, speaks for an assignment to the polychaeta . Work by Dieter Bunke from the 1980s showed that the sperm of the aphanoneura differ so greatly from those of the oligocha that they cannot belong to this group. Molecular genetic studies by Rousset et al. 2007 as well as by Zrzavý et al. 2009 support the thesis that the aphanoneura are by no means more closely related to the oligochaetes than to any other annelids.
The Aeolosomatidae and Potamodrilidae also show individual noticeable differences: The former reproduce largely asexually, while the latter only reproduce sexually. However, several more recent molecular genetic studies such as 2001 by Rota, Martin and Erséus or 2005 by Struck and Purschke confirm the two families as sister groups and thus the Aphanoneura as a monophyletic group.
literature
- František Vejdovský: System and Morphology of the Oligochaetes. Comité for the Natural History of Bohemia, Franz Řivnáč, Prague 1884. Aphanoneura. P. 16.
- E. Rota, Y. de Jong: Fauna Europaea: Annelida - Terrestrial Oligochaeta (Enchytraeidae and Megadrili), Aphanoneura and Polychaeta. In: Biodiversity data journal. Number 3, 2015, p. E5737, doi : 10.3897 / BDJ.3.e5737 , PMID 26379463 , PMC 4568407 (free full text).
- 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.
- 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.
- 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.
- Piet FM Verdonschot: Phylum Annelida. In: James H. Thorp, D. Christopher Rogers: Thorp and Covich's Freshwater Invertebrates: Ecology and General Biology. Elsevier, Amsterdam 2014. pp. 509-590, here pp. 523f.
- DA Lastochkin (1935): Two new river Aeolosomatidae (Oligochaeta limicola). Annals and Magazine of Natural History, Series 10, No. 15 (90): p. 636–645, here 637–643, fig. 1–5, doi : 10.1080 / 00222933508655011
- 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
- D. Bunke: Ultrastructure of the spermatozoon and spermiogenesis in the interstitial annelid Potamodrilus fluviatilis. In: Journal of Morphology. Volume 185, Number 2, August 1985, pp. 203-216, doi : 10.1002 / jmor.1051850206 , PMID 30016849 .
- Dieter Bunke (1986): Ultrastructural investigations on the spermatozoon and its genesis in Aeolosoma litorale with considerations on the phylogenetic implications for the Aeolosomatidae (Annelida). Journal of Ultrastructure and Molecular Structure Research 95, pp. 113-130. doi : 10.1016 / 0889-1605 (86) 90035-2
- Emilia Rota, Patrick Martin, Christer Erséus (2001): Soil-dwelling polychaetes: enigmatic as ever? Some hints on their phylogenetic relationships as suggested by maximum parsimony analysis of 18S rDNA gene sequences. Contributions to Zoology, 70 (3), pp. 127-138.
- Torsten H. Struck, Günter Purschke (2005): The sister group relationship of Aeolosomatidae and Potamodrilidae (Annelida: “Polychaeta”) - a molecular phylogenetic approach based on 18S rDNA and cytochrome oxidase I. Zoologischer Anzeiger - A Journal of Comparative Zoology 243 ( 4), pp. 281-293. doi : 10.1016 / j.jcz.2005.01.001
- J. Zrzavý, P. Ríha, L. Piálek, J. Janouskovec: Phylogeny of Annelida (Lophotrochozoa): total-evidence analysis of morphology and six genes. In: BMC Evolutionary Biology. Volume 9, August 2009, p. 189, doi : 10.1186 / 1471-2148-9-189 , PMID 19660115 , PMC 2732625 (free full text).
- Vincent Rousset, Fredrik Pleijel u. a .: A molecular phylogeny of annelids. In: Cladistics. 23, 2007, p. 41, doi : 10.1111 / j.1096-0031.2006.00128.x .