Lung snails

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Lung snails
Grove cepaea (Cepaea nemoralis)

Grove cepaea ( Cepaea nemoralis )

Systematics
Trunk : Molluscs (mollusca)
Class : Snails (gastropoda)
Subclass : Orthogastropoda
Superordinate : Heterobranchia
Order : Lung snails
Scientific name
Pulmonates
Cuvier in Blainville , 1814

The pulmonary snails (Pulmonata, from Latin pulmo "lung") are a group of snails (Gastropoda) with many shapes and are traditionally referred to as order. They are among the few representatives of the molluscs that have colonized the mainland, but they are also found in fresh water and sometimes in the sea. In the landforms, the mantle cavity serves to breathe air, from which the name pulmonary snail is derived.

According to current knowledge, lung snails do not represent a natural taxon , but a paraphyletic group because they do not contain all of the descendants of their last common ancestor . They are therefore referred to as a group in phylogenetic systematic representations and / or written in quotation marks ("Pulmonata", "Lung snails iwS"). According to current knowledge, however, the eupulmonata (lung snails in the sense of the word ) are a real monophyletic taxon , which essentially summarizes the taxa previously known as " land snails ".

features

The lung snails no longer have the gills created in the snail's blueprint , but numerous aquatic inhabitants have developed secondary gills. On the vascular ceiling of the mantle cavity, which is used for breathing, there is an opening (pneumostome) that regularly opens and closes and leads into a cavity. Due to its function as a respiratory organ, it is also referred to as the lungs and gave the group its name. However, many aquatic lung snails do not need to rise to the surface of the water to pump air into the mantle cavity, but can instead carry out their gas metabolism directly via the water phase.

The basic pattern of the pulmonary snails' characteristics includes a shell into which the animal can completely withdraw. However, an operculum to close the housing has been lost in the evolutionary line to the pulmonary snails. In some groups, the housing has been reduced so much that the animal can no longer fully retreat into the housing. Sometimes the case is completely missing from the outside. In some groups of the so-called " nudibranchs ", only a small lime plate remains in the mantle, which serves as a lime reservoir. The shell of the pulmonary snail is rolled up in the basic pattern and consists of three layers: an outer organic layer (periostracum), a middle aragonitic prismatic layer and an inner aragonitic cross-lamellar layer. The shell is formed by glands on the edge of the mantle. A (slight) growth in thickness and the repair of the shell can take place on almost the entire surface of the shell. The torsion (twisting of the soft body) belonging to the basic pattern of snails has been reversed convergently in some groups of nudibranchs ("detorsion").

Reproductive biology

Lung snails are hermaphrodites that fertilize each other alternately. In some species self-fertilization also occurs (to varying degrees) . Lung snails lay up to several hundred yolk-rich or egg-white-rich eggs, from which the young snails hatch after a few weeks. The development is direct, i.e. without a larval stage.

Way of life

The lung snails have opened up a habitat with the land surface that has remained closed to most other mollusks. They occur in the intertidal area, in natural and cultural landscapes and even in human dwellings from the plains to the high mountains at 6000 m altitude. Some species mainly live in the soil. They have even penetrated into the arid regions and deserts of the earth. They also colonize limnic ecosystems very successfully , including brackish water and the sea.

Lung snails as pests

Compared with other groups of snails, there are relatively many species among the pulmonary snails that can be described as pests from a human point of view or that act as vectors of disease. This is of course due to the terrestrial and limnic way of life of most species of lung snail, which easily come into contact with humans and their crops. However, it must be emphasized that in absolute terms there are only a few species that actually cause noticeable damage to crops. Species often only became problematic when they were dragged from their original habitat to other regions. The vast majority of lung snails are harmless and play an important role in the ecosystem. Under no circumstances should they be fought or indiscriminately collected. Here is a compilation of the most important lung snail species that can cause damage (according to Godan, 1999). Many of the species listed are now distributed worldwide.

Lung snails as carriers of disease

In the countries of the tropics, different species of lung snails (e.g. Bulinus and Biomphalaria ) are fought as intermediate hosts of the pair of leeches Schistosoma (different species), which can cause schistosomiasis . Humans are the primary host in some species of Schistosoma , while grazing animals, poultry, and domestic animals are the main hosts in others. Different species of the Lymnaeidae are intermediate hosts for the large liver fluke ( Fasciola hepatica ), which can trigger the fasciolosis in the ultimate host (mammals) . Some lungworms need snails, mostly lung snails, as intermediate hosts. Lung snails also play a major role as carriers of plant diseases. The tobacco mosaic virus can be transmitted by Deroceras reticulatum . This species can also transmit the bacterium Corynebacterium insidiosum , which damages alfalfa . The bacterium Pectobacterium carotovorum causes the rotting of various cruciferous plants . Fungal spores are very often transmitted by lung snails.

Species number

The information on the number of species of the pulmonate snail is highly variable. This is due to the often controversial division of the often form-rich groups into more or less species. There are total numbers of 16,000 to over 30,000 species. The vast majority of species live on the dry mainland. Some groups also live in fresh water, some in brackish water and in the sea. The hazard situation is different; Many freshwater species are considered to be particularly endangered, many of which are already extinct.

Systematics

The lung snail group has long been considered a monophyletic taxon. An important basis were certain morphological peculiarities, such as the so-called streptoneure innervation of the head tentacles and the lack of a rhinophore nerve. In addition to refined morphological analyzes, however, it is in particular a rapidly growing number of molecular genetic studies that have shown that the "pulmonary snails" represent a paraphyletic group.

The following orientational compilation follows the principle of the classification by Bouchet & Rocroi (2005). In these authors, the "pulmonary snails" are referred to as a group ("informal group"), not as an order . These authors have also dispensed with all category designations above the superfamily in their classification . The "Basommatophora" also form only one such (paraphyletic) group. However, according to the latest findings, monophyletic taxa are also the Eupulmonata and the Stylommatophora.

Classification of lung snails based on phylogenetic analysis , following Bouchet & Rocroi (2005), simplified

Individual evidence

  1. ^ Philippe Bouchet, Jean-Pierre Rocroi: Part 2. Working classification of the Gastropoda . In: Malacologia, 47: 239-283, Ann Arbor 2005 ISSN  0076-2997
  2. ↑ Klussmann-Kolb , A., Dinapoli, A., Kuhn, K., Streit, B., Albrecht, C .: From sea to land and beyond - New insights into the evolution of euthyneuran Gastropoda (Mollusca). BMC Evolutionary Biology 2008, 8:57. doi : 10.1186 / 1471-2148-8-57 (2008)
  3. ↑ Christina Grande, José Templado, Rafael Zardoya: Evolution of gastropod mitochondrial genome arrangements. BMC Evolutionary Biology 8:61 doi : 10.1186 / 1471-2148-8-61 (2008)

literature

  • Winston Ponder & David Lindberg: Towards a phylogeny of gastropod molluscs; an analysis using morphological characters . In: Zoological Journal of the Linnean Society. 119: 83-265, London 1997 ISSN  0024-4082
  • Dora Godan: Molluscs Their Significance for Science, Medicine, Commerce and Culture. 203 pp., Parey Buchverlag Berlin 1999 ISBN 3-8263-3228-8
  • Christopher M. Wade, Peter B. Mordan, and Fred Naggs: Evolutionary relationships among the Pulmonate land snails and slugs (Pulmonata, Stylommatophora). In: Biological Journal of the Linnean Society, 87: 593-610, Oxford 2006 ISSN  0024-4066

Web links

Commons : Category: Lung snails  - Collection of images, videos and audio files