Ferrissia

The genus belongs to the family of Ferrissia plate screw ( Planorbidae ) and includes a larger number of species that occur in the freshwater world. The types are characterized by cup-shaped 3-6 mm shells. In Central Europe, living the traditional ( since 1960), known as Ferrissia wautieri species whose status (possible synonymisation to one or more non-European species, introduced or indigenous? ) Is not yet fully understood; this type (or types ) are sometimes referred to in English as Septenmützenschnecke.

Features

Morphology: The genus is not very precisely defined, which is why representatives have been variously described under other generic names (eg Gundlachia ). The apex of Ferrissia is unlike Ancylus provided with very finely sculptured Radiärrippen and he is never hook-shaped. In many cases, can form a septum (often about two- thirds) closes the shell from the bottom rear part and relieved to survive the dry spells along the shell opening. After a re- onset growth spurt may thus form a strange double scheduled shell. The copulatory organs are characterized by the possession of a flagellum. Aphallische individuals (ie, individuals without a penis, which can therefore act only as females ) are relatively common.

Karyology: At least some of the representatives of Ferrissia have a tetraploid chromosome number of n = 30 (compared to the base number of the Planorbidae 15-18 ), as was reported for F. parallela and F. tarda.

Similar Species

Confusion with the genera Gundlachia and Ancylus have occurred several times in science.

In Europe and for the layman the greatest likelihood of confusion found here Ferrissia forms is another. Furthermore, there is a likelihood of confusion with juvenile river cap screw and also with about the same size Teichnapfschnecke that in contrast to all plate screw is anatomically rechtsgewunden however.

Distribution and occurrence

The genus occurs on several continents. Whether occurring in Europe forms represent native species or one or more introduced species, is still unclear. The species of the genus Ferrissia also occur in temporary waters and irrigation channels in rivers and lakes in arid areas.

System

The outer scheme is explained in Planorbidae. Then Ferrissia belongs together with other genera ( Ancylus, Gundlachia, Laevapex, Hebetancylus ) to Tribus Ancylini.

Internal system: The number of species can not be specified because of the large variability, especially as sound genetic comparative studies at the species level hardly exist. Usually nowadays listed on the 30 species worldwide. The following are some of the more common types mentioned, it being expected that in future also with renaming, splitting and reassignments:

  • Ferrissia clessiniana Jickeli 1882 is partly seen as a synonym of F. fragilis or to the European F. wautieri
  • Ferrissia dalli (as "fragile ancylid ") is
  • Ferrissia fragilis Tryon, 1863 ( in North America called "fragile ancylid "). The species lives in small standing waters and can survive by forming a septum, and drought. They consumed preferably diatoms, which they rasp of higher water plants such as water lilies. The species is likely to be deported now global and corresponds in Europe might F. wautieri
  • Ferrissia hendersoni (Walker, 1908), ( in North America called " blackwater ancylid " )
  • Ferrissia isseli ( Bourguignat, 1866), Egypt, Ethiopia, Sudan, perhaps; to 3.7 mm
  • Ferrissia mcneili Walker, 1925, endemic to the U.S. (as "hood ancylid ") which applies under the IUCN as threatened ( " vulnerable" )
  • Ferrissia parallela / parallelus ( dump man, 1841) ( in North America called " oblong ancylid " ), in standing waters
  • Ferrissia rivularis (Say, 1817), the USA and Canada ( in North America called " creeping ancylid " ), in running or otherwise moving waters
  • Ferrissia tanganyicensis Smith, 1906, only Lake Tanganyika, but here spread (on the hard substrates of all shore areas, up to 100 m depth). Applies under the IUCN as endangered not
  • Ferrissia tarda ( Say)
  • Ferrissia walkeri ( Pilsbry & Ferriss, 1907), North America ( in North America as " Cloch ancylid ") is
  • Ferrissia wautieri Mirolli, 1960, Septenmützenschnecke, to 3.9 mm. The formation of the septum, which is responsible for the species name in German, can be induced by environmental conditions and does not always occur. 1960 first found in Italy and France and, soon after, in Germany and elsewhere, and scientifically described. Subsequent verifications of older collection materials have shown that the way in some countries ( Germany, Czech Republic and others) for decades previously found, but not recognized or has been specifically noted. The final designation and possible synonymisation to North American and perhaps brought in with introduction to Europe forms is still in flux
Gundlachia (gastropod)
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