Troglochaetus beranecki
| Troglochaetus beranecki | ||||||||||
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| Troglochaetus beranecki | ||||||||||
| Delachaux , 1921 |
Troglochaetus beranecki is asmall species of polychetes that lives in the groundwater . It is the onlyspecies of its familythat lives in freshwater and one of only a few freshwater-living representatives of the predominantly marine (in the sea) polychetes worldwide. He belongs to the "Archiannelida" or "Urringelworms", a group of small representatives with a simple physique, whose systematic position is uncertain. As the only representative of its relatives living there, it is sometimes simply referred to as "primeval ringworm" when it occurs in the groundwater.
description
The whitish-translucent colored annelid worm reaches a body length of about 0.6 to 0.7 millimeters. Its body is made up of eight segments . On the anterior segment sits a head flap or prostomium , which carries two very conspicuous club-shaped buttons or palps. At the rear edge of the prostomium sit two so-called nuchal organs, ciliate dimples, which presumably serve as sensory organs. In contrast to most related species, antennas are absent. All body segments have very short parapodia , leg-like appendages formed in two lobes , these have two bundles of long, conspicuous bristles (setae), except for the first with only one bundle. The very thin bristles are longer than the body diameter. Since the cuticle is only thin and flexible, the worm appears soft-skinned. At the rearmost part of the body, the pygidium, sit two small flagellated, lobed appendages.
Troglochaetus is a hermaphroditic hermaphrodite, i. H. the individuals have both male and female gonads. The only pair of sperm products has openings in the sixth segment, the oviducts in the eighth segment. The fertilization takes place externally. The new generation develops from the fertilized eggs in direct development, without larval stages. Ripe eggs reach about 100 micrometers in length; they are presumably also nourished in the oviduct by excess eggs that remain small and are later resorbed.
In all Nerillidae, the inner body cavity, the coelom acting as a hydroskeleton , is not lined by an epithelium . It is unknown whether the species has a blood vessel system, but it is probably missing. Protonephridia are present as excretory organs .
Ecology and way of life
Troglochaetus beranecki is a groundwater animal and is considered a species that specializes in this habitat and rarely occurs in other limnic habitats, so it belongs to the Stygobionta . More rarely, however, it is also given from the system of gaps below surface water, the so-called hyporheic interstitial . Since all related species, including the second member of the genus, live in the sea, it is believed that the ancestors of the species probably got here by direct routes from marine habitats, presumably via the coastal sandgap fauna . It moves by ciliary sliding in the narrow, water-filled cavities between the grains of the soil matrix. The diet has not been researched, presumably it feeds itself, like the related species of bacteria and detritus .
distribution
The species was first described by Théodore Delachaux in 1919 in the Grotte du Ver, a cave in the Areuse gorge in the canton of Neuchâtel , Switzerland. It was later found in large parts of Europe, including France, Germany, Austria, Poland, Hungary, Romania and Italy's Trentino. The species occurs north to Finland and, in the Arlberg area in Austria, at sea levels of up to 2000 meters. In Germany it is considered widespread, but is rarely found.
Surprisingly, animals that are morphologically indistinguishable were also found in the Rocky Mountains of Colorado, USA, in 1996. Here some editors suspect a morphologically indistinguishable cryptospecies . Since long-distance distribution of the species seems extremely unlikely, an occurrence on two continents would be an indication of its very old age.
Systematics and phylogeny
The species is the only limnic representative of the Nerillidae family, a group of annelids that are mainly found in marine sediments. The genus Nerillidium is probably closely related to the genus Troglochaetus . In fact, a marine species previously assigned to this genus was transferred to the previously monotypic genus as Troglochaetus simplex due to the investigation .
The Nerillidae form a group with a few similarly small, polychaete annelid worms with a simple physique, which is called "Archiannelida". It was considered almost certain that these “primordial ringworms” are actually a group of dwarf, possibly neotenic species with a secondary simplified physique, possibly due to the habitat in the gap system, which offers little space. Unexpectedly, however, most of them actually turned out to be potentially closely related clades in an analysis .
Unlike the little bristle or oligochaeta, the polychetes are rare in fresh water. In total, fewer than 100 species are known here, only 9 of them living in the groundwater. None of the other types of groundwater occur in Europe.
Individual evidence
- ↑ a b Katrineholm Worsaae: Nerillidae Levinsen, 1883. In: Wilfried Westheide, Günter Purschke (editors): Annelida: polychaetes. In: Andreas Schmidt-Rhaesa (editor in chief): Handbook of Zoology. A Natural History of the Phyla of the Animal Kingdom. De Gruyter, Copenhagen, 2014.
- ↑ A Vandel: Biospeleology, The Biology of Animals cavernicolous. Pergamon Press, Oxford 1965. on page 69.
- ↑ Ivano Morselli, Marisia Mari, Manuela Sarto (1995): First record of the stygobiont "archiannelid" Troglochaetus beran ecki Delachaux from Italy. Bolletino di zoologia 62: 287-290.
- ^ Andreas Fuchs, Hans Jürgen Hahn, Klaus-Peter Barufke: Groundwater monitoring program. Survey and description of the groundwater fauna in Baden-Württemberg. published by the LUBW State Institute for the Environment, Measurements and Nature Conservation Baden-Württemberg. Groundwater protection series, Volume 32. Karlsruhe, 2006.
- ↑ Robert W. Pennak (1971): A Fresh-Water Archiannelid from the Colorado Rocky Mountains. Transactions of the American Microscopical Society 90 (3): 372-375.
- ^ Katrine Worsaae & Reinhardt Møbjerg Kristensen (2005): Evolution of interstitial Polychaeta (Annelida). Hydrobiologia 535/536: 319-340. doi : 10.1007 / 1-4020-3240-4_18
- ↑ Katrine Worsaae (2005): Phylogeny of Nerillidae (Polychaeta, Annelida) as inferred from combined 18S rDNA and morphological data. Cladistics 21: 143-162. doi : 10.1111 / j.1096-0031.2005.00058.x
- ↑ Jan Zrzavý, Pavel Říha, Lubomír Piálek, Jan Janouškovec (2009): Phylogeny of Annelida (Lophotrochozoa): total-evidence analysis of morphology and six genes. BMC Evolutionary Biology 2009, 9: 189 doi : 10.1186 / 1471-2148-9-189
- ↑ Christopher J. Glasby & Tarmo Timm (2008): Global diversity of polychaetes (Polychaeta; Annelida) in freshwater. Hydrobiologia 595: 107-115. doi : 10.1007 / s10750-007-9008-2