Ferrissia
| Ferrissia | ||||||||||
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Ferissia clessiana |
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| Scientific name | ||||||||||
| Ferrissia | ||||||||||
| Walker , 1903 |
The genus Ferrissia belongs to the family of the pancake snails (Planorbidae) and includes a large number of species that occur in freshwater worldwide. The species are characterized by bowl-shaped, approx. 3–6 mm large shells. The species traditionally known as Ferrissia wautieri (since 1960) lives in Central Europe , the status of which (possible synonymisation to one or more non-European species, introduced or indigenous?) Has not yet been conclusively clarified; this species (or species) are sometimes referred to in German as the septum snail .
features
Morphology : The genus is not defined very precisely, which is why representatives have been described variously under other generic names (e.g. Gundlachia ). In contrast to the Ancylus, the apex of Ferrissia has very finely sculpted radial ribs and it is never hook-shaped. In many cases, a septum can form along the opening of the bowl, which partially closes the bowl from below (often about two thirds) and makes it easier to survive dry periods. After a new growth spurt , a strange double-attached shell can form. The copulatory organs are distinguished by having a flagellum. Aphallic individuals (i.e., individuals without a penis who can therefore only function 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 15 to 18 of the Planorbidae), as was reported for F. parallela and F. tarda .
Similar species
Confusion with the genera Gundlachia and Ancylus has also occurred variously in science.
In Europe and for laypeople, there is the greatest risk of confusion between the Ferrissia forms found here . Furthermore, there is a risk of confusion with juvenile river cap snails as well as with the pond snail , which is roughly the same size , but unlike all pancake snails , it is anatomically right-wound.
Distribution and occurrence
The genus occurs on several continents. It is still unclear whether the forms occurring in Europe represent native species or one or more introduced species. The species of the genus Ferrissia occur in rivers and lakes, in dry areas also in temporary waters and irrigation channels.
Systematics
The external system is explained under Planorbidae . According to this, Ferrissia belongs together with other genera ( Ancylus , Gundlachia , Laevapex , Hebetancylus ) to the Ancylini tribe .
Internal systematics : The number of species cannot be specified due to the great variability, especially since well-founded genetic comparative studies at the species level are hardly available. Usually around 30 species are listed around the world today. The following are some of the more frequently mentioned types, although renaming, splitting and reallocation are to be expected in the future:
- Ferrissia clessiniana Jickeli, 1882 is partly as a synonym of F. fragilis or the European F. wautieri seen
- Ferrissia dalli (referred to as "fragile ancylid")
- Ferrissia fragilis Tryon, 1863 (referred to as "fragile ancylid" in North America). The species lives in small stagnant waters and can survive dry periods through the formation of a septum. She prefers to consume diatoms , which shescrapesoff higher aquatic plants such as pond roses. The species is now likely to have been introduced globally and possibly corresponds to F. wautieri in Europe
- Ferrissia hendersoni (Walker, 1908), (called "blackwater ancylid" in North America)
- Ferrissia isseli (Bourguignat, 1866), Egypt, Ethiopia, perhaps Sudan; up to 3.7 mm
- Ferrissia mcneili Walker, 1925, endemic to the USA (referred to as "hood ancylid"), classified as threatened ("vulnerable") according to the IUCN
- Ferrissia parallela / parallelus (Haldemann, 1841) (referred to in North America as "oblong ancylid"), in stagnant waters
- Ferrissia rivularis (Say, 1817), USA and Canada (referred to as "creeping ancylid" in North America), in flowing or otherwise agitated waters
- Ferrissia tanganyicensis Smith, 1906, only Lake Tanganyika , but widespread here (on the hard substrates of all bank areas, up to 100 m depth). Is considered not at risk according to IUCN
- Ferrissia tarda (Say)
- Ferrissia walkeri (Pilsbry & Ferriss, 1907), North America (referred to as "cloch ancylid" in North America)
- Ferrissia wautieri Mirolli, 1960, septum cap snail , up 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. Found and scientifically described in 1960, first in Italy and France and soon afterwards in Germany and elsewhere. Subsequent examinations of older collection materials have shown that the species was found decades earlier in some countries (Germany, the Czech Republic, etc.), but was not recognized or specifically noted. The final designation and possible synonymisation to North American forms that may have come to Europe as a result of importation is currently still in flux
literature
- Allspach, A. (1983): First record of the cap snail Ferrissia wautieri (MIROLLI 1960), for Hesse. - Hess. faunist. Letters, 1983: 46-50.
- Allspach, A. (1986): First record of the cap snail Ferrissia wautieri (MIROLLI 1960) for Lower Saxony. - Contributions to the natural history of Lower Saxony, 1986: 30-32.
Individual evidence
- ↑ CM Patterson, JB Burch: Chromosomes of pulmonate molluscs. Pp. 171-217, in: V. Fretter, J. Peake, Pulmonates . Vol. 2A, Academic Press, London (1978)
- ↑ Albrecht, C., Kuhn, K., Streit, B .: A molecular phylogeny of Planorboidea (Gastropoda, Pulmonata): Insights from enhanced taxon sampling. Zoologica Scripta 36: 27-39 (2007).
- ↑ DW Blinn, RE Truitt, A. Pickart: Feeding ecology and radular morphology of the freshwater limpet Ferrissia fragilis . JN Am. Benthol. Soc. 8: 237-242 (1989)
- ↑ Ferrissia mcneili
- ↑ Ferrissia tanganyicensis
- ↑ Beran L. & Horsák M .: Distribution of the alien freshwater snail Ferrissia fragilis (Tryon, 1863) (Gastropoda: Planorbidae) in the Czech Republic. - Aquatic Invasions 2 (1): 45-54 (2007)