Cuttlefish

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Cuttlefish
Ramshorn snail (Planorbarius corneus)

Ramshorn snail ( Planorbarius corneus )

Systematics
Trunk : Molluscs (mollusca)
Class : Snails (gastropoda)
Order : Lung snails (pulmonata)
Subordination : Water lung snails (Basommatophora)
Family : Cuttlefish
Scientific name
Planorbidae
Rafinesque , 1815

The family of the plate snails (Planorbidae) belongs within the order of the lung snails to the water lung snails (Basommatophora). For some years the representatives of the cap snails (formerly "Ancylidae" ) belong to the family of poppy snails (for details see systematics).

A well-known and striking representative is the ramshorn snail , which occurs in calm waters (ponds, ponds, oxbow lakes) in Central Europe (see fig.); it is not to be confused with the genus of the post squirrel ( Gyraulus ), which also belongs to the plate snails . A picture of a member of the cap-shaped species of this snail family can be found under river cap snail . There are also cone-shaped ( Gyraulus ) species.

features

Morphology : The cephalic snails are anatomically left-wound and share this property with the bladder snails (Physidae). Therefore, in the crawling animal, the right side is to be addressed as the underside and the left side as the upper side. The shape of the housing can, however, vary from disk-shaped to cup-shaped. In the case of representatives with a disk-shaped housing, the housing is usually kept tilted at an angle. The base of the forms with a disc-shaped housing is always relatively small and the feelers are thin and slim. A secondary gill is typically present within the mantle cavity. Some forms are colored conspicuously red by hemoglobin, which is never the case with other representatives of the aquatic snail.

Karyology : While the number of chromosomes in water snails is often fairly constant within individual families, it is relatively variable in the Planorbidae. The basic number in the haploid state is n = 17 or n = 18, but can also assume n = 15. Interestingly, a number of species of the family (both the disk-shaped and the cup-shaped representatives) tend to double the base number; Such a tetraploidy with accordingly n = 30-36 chromosomes is found in species of the genera Ancylus , Bulinus , Ferrissia and Gyraulus . Even hexaploidy and octoploidy have been described (in species or genetic lines of bulinus and ancylus ).

Anatomy and physiology

Anatomy : Shell and anatomical properties are very variable, which is particularly true of the hermaphroditic reproductive system (penis, hermaphroditic gland (ovotestis) and the prostate gland). In some species there are populations with partially aphallic individuals (i.e. individuals without a penis), which consequently can only function as females. The primary hermaphroditism in these forms has been modified in the direction of a functional segregated gender.

Respiration : Many species have a red colored hemolymph due to hemoglobin , which means that the oxygen absorbed from the water or the air can probably be better used for the metabolism than the hemocyanin, which is used for this function in other molluscs . As a result of this and the formation of a secondary gill in the lung cavity, the representatives of this family are able to colonize waters with difficult respiratory conditions and sometimes (in the case of the cup-shaped forms even entirely or almost exclusively) get along without atmospheric oxygen.

Diet : The animals graze on solid bases with their radula and thus primarily consume algae (green algae, diatoms), but also other small organisms.

Reproductive biology

Reproduction : Like all water pulmonary snails, the pinnacle snails are also hermaphroditic . In many populations, the animals are not only capable of cross-fertilization, but also of self-fertilization. However, in some species (e.g. Bulinus truncatus ) there are populations whose animals do not develop any penis (aphallic animals); these animals only act as females when mating or perform self-fertilization.

Clutches of the Planorbidae are glued to the underside of leaves, stones and wood, in aquariums also to the pane. They are round, oval or kidney-shaped and consist of a clear jelly that contains one to ten eggs in the smaller species and around ten to thirty eggs in the larger species. However, the number of eggs also varies according to the nutritional status and the individual size, which continues to increase even after the onset of sexual maturity. In the case of the genus Protancylus , which occurs in geologically ancient lakes in Indonesia , brood care has been observed, which is unique among aquatic snails; the animals carry the egg clutches protectively under their coat.

Distribution and number of species

Global distribution : The pinnacle snails are distributed worldwide. This applies both to the "classic" plate snails with a disk-shaped housing and to the representatives with a bowl-shaped shell. From this it can be concluded either that the family is very old in terms of geological history or that the family has a strong ability to spread (e.g. displacement via birds).

Species number : The family comprises around 40 genera with around 300 species; of the latter, around 200 species are the "classic" pancake snails with disk-shaped shells and around 100 species are the cup-shaped representatives, the earlier "Ancylidae". More than 70 genera are nominally described; a modern taxonomic revision of the family, which takes into account morphological and molecular data, is pending. Hubendick created the last critical overall representations (based on anatomical-morphological findings) in 1955 and 1964.

In Germany there are currently ten genera with 21 species, including the introduced forms, two of which have one species each with a cup-shaped shell. The exact number of species cannot be given because some forms are classified as separate species or subspecies in the river. Without the species introduced since the middle of the 20th century, there are eight genera with 17 species, one of which is cup-shaped (genera Planorbis, Anisus, Bathyomphylus, Gyraulus, Hippeutis, Segmentina, Planorbarius, Ancylus) ; two new genera and a total of four species have been introduced safely or probably: Menetus dilatatus , Ferrissia "wautieri" , Gyraulus parvus and G. chinensis .

paleontology

Fossil disc-shaped representatives from the subfamilies of the Planorbinae and Bulininae have occurred geologically since the Middle Jurassic (around 170 million years ago). The cup-shaped forms, which were formerly referred to as "Ancylidae", have been found (although their assignment is uncertain) since the Upper Cretaceous , with greater certainty since the early Paleocene around 60 million years ago. The correct taxonomic assignment of the fossil shell finds is almost entirely uncertain. It was not until the Miocene that forms were found that are very reminiscent of our current genera and species, e.g. B. the species Planorbarius grandis (Halavats) and Segmentina loczyi (Lörenthey) from the then Pannon Lake (late Miocene 10-11 million years ago) of the Vienna Basin.

Systematics

External system : Often the pancake snails are grouped together with the bladder snails in a superfamily ( Planorboidea ). With the bladder snails they share the characteristics that they are anatomically left-wound and that they develop long and thin (thread-like) antennae, which only become a bit thicker in the cup-shaped representatives. More recent molecular genetic findings also suggest that these two families are closely related.

Internal systematics : The earlier family "Ancylidae" is seen today as a paraphyletic group due to molecular genetic relationships and is generally associated with the family Planorbidae. It is now represented as a tribe within this family with some of its representatives ; others of their representatives are found elsewhere within the Planorbidae. The former subfamily Ferrissinae (within the Ancylidae) was completely abandoned.

Two systems currently under discussion are presented below:

a) current classification based on Albrecht et al. (2007) , whereby only those genera are listed that were analyzed:

b) Classification based on Bouchet & Rocroi (2005) :

  • Subfamily Planorbinae Rafinesque-Schmaltz, 1815
    • Tribus Planorbinae Rafinesque-Schmaltz, 1815
    • Tribus Ancylini Rafinesque-Schmaltz, 1815
    • Tribus Biomphalariinae Watson, 1954
    • Tribus Planorbulinae Pilsbry, 1934
    • Tribus Segmentini Baker, 1945
  • Subfamily Bulininae Fischer & Crosse, 1880
    • Tribus Bulinini Fischer & Crosse, 1880
    • Tribus Coretini Gray, 1847
    • P. Miratestini & F. Sarasin, 1897
    • Tribus Plesiophysidae Bequaert & Clench, 1939
  • Subfamily Neoplanorbinae Hannibal, 1912
  • Subfamily Rhodacmaeinae Walker, 1917

Individual evidence

  1. ^ Gyraulus. In: Red Lists of Endangered Animals in Austria. Volume 14/2, pp. 386/87, Böhlau Verlag 2007, ISBN 978-3-205-77478-5 . (books.google.de) Retrieved June 5, 2013.
  2. ↑ T. Städler, M. Loew, B. Streit: Genetic evidence for low outcrossing rates in polyploid freshwater snails ( Ancylus fluviatilis ). In: Proc. Royal Soc. London B. Volume 251, 1993, pp. 207-213.
  3. ^ Christian Albrecht, Matthias Glaubrecht: Brood care among basommatophorans: a unique reproductive strategy in the freshwater limpet snail Protancylus (Heterobranchia: Protancylidae), endemic to ancient lakes on Sulawesi, Indonesia. 2006.
  4. ↑ B. Hubendick: Phylogeny in the Planorbidae. In: Transactions of the Zoological Society of London. Volume 28, 1955, pp. 453-542.
  5. ↑ B. Hubendick: Studies on Ancylidae. The subgroups. In: Meddelanden från Göteborgs Musei Zoologiska Avdelning. Volume 137, 1964, pp. 1-71.
  6. ↑ Peter Glöer: The animal world of Germany. Mollusca I Freshwater gastropods of Northern and Central Europe Key to identification, way of life, distribution. 2., rework. Edition. ConchBooks, Hackenheim 2002, ISBN 3-925919-60-0 .
  7. ^ MJ Benton (Ed.): The Fossil Record 2. Chapman & Hall, London 1993.
  8. ↑ M. Harzhauser, PM Tempfer: Late Pannonian wetland ecology of the Vienna Basin based on molluscs and lower vertebrate assemblages (Late Miocene, MN 9, Austria). In: Cour. Research Inst. Senckenberg. Volume 246, 2004, pp. 55-68.
  9. Jump up ↑ A. Klussmann-Kolb , A. Dinapoli, K. Kuhn, B. Streit, C. Albrecht: From sea to land and beyond - New insights into the evolution of euthyneuran Gastropoda (Mollusca). In: BMC Evolutionary Biology. Volume 8, 2008, p. 57. doi: 10.1186 / 1471-2148-8-57 .
  10. Jump up ↑ Christian Albrecht, Kerstin Kuhn, Bruno Streit: A molecular phylogeny of Planorboidea (Gastropoda, Pulmonata): insights from enhanced taxon sampling. In: Zoologica Scripta. (Oxford). Volume 36, 2007, pp. 27-39.
  11. ^ Philippe Bouchet, Jean-Pierre Rocroi: Part 2. Working classification of the Gastropoda. In: Malacologia. (Ann Arbor). Volume 47, 2005, pp. 239-283. ISSN  0076-2997

Further literature

  • Victor Millard: Classification of the Mollusca. A Classification of World Wide Mollusca . Rhine Road, South Africa 1997, ISBN 0-620-21261-6 .

Web links

Commons : Planorbidae  - Collection of images, videos and audio files