The Gastropoda reference article from the English Wikipedia on 24-Jul-2004
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Gastropoda

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Gastropods
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Scientific classification
Kingdom:Animalia
Phylum:Mollusca
Class:Gastropoda
Order
Subclass Eogastropoda
    Patellogastropoda
Subclass Orthogastropoda
  Superorder Cocculiniformia
  Superorder Hot Vent Taxa
    Neomphaolida
  Superorder Vetigastropoda
  Superorder Neritaemorphi
    Neritopsina
  Superorder Caenogastropoda
    Architaenioglossa
    Sorbeoconcha
  Superorder Heterobranchia
    Heterostropha
    Opisthobranchia
    Pulmonata

The gastropods, or univalves, are the largest and most successful class of molluscs, with 60,000-75,000 species, and second largest class of animals, with over 100,000 species, comprising the snails and slugs, as well as a vast number of marine and freshwater species.

They typically have a well-defined head with two or four sensory tentacles, and a ventral foot, which gives them their name (Greek gaster, stomach, and poda, feet).

They are distinguished by torsion, a process where the body coils to one side during development.

Most members have a shell, which is in one piece and typically coiled or spiralled that usually opens on the right hand side (as viewed with the shell apex pointing upward). Several species have an operculum that operates as a trapdoor to close the shell. This is usually made of a horny material, but in some molluscs it is calcareous. In some members, the slugs, the shell is reduced or absent, and the body is streamlined so its torsion is relatively inconspicuous.

While the best-known gastropods are terrestrial, more than two thirds of all species live in a marine environment. Marine gastropods include herbivores, detritus feeders, carnivores and a few ciliary feeders, in which the radula is reduced or absent. The radula is usually adapted to the food that a species eats. The simplest gastropods are the limpets and abalones, both herbivores that use their hard radulas to rasp at seaweeds on rocks. Many marine gastropods are burrowers and have siphons or tubes that extend from the mantle and sometimes the shell. These act as snorkels, enabling the animal to continue to draw in a water current containing oxygen and food into their bodies. The siphons are also used to detect prey from a distance. These gastropods breathe with gills, but some freshwater species and almost all terrestric species have developed lungs. While the gastropods with lungs all belong to one group (Pulmonata), the gastropods with gills are paraphyletic.

Sea slugs are often flamboyantly coloured, either as a warning if they are poisonous, or to camouflage them on the corals and seaweeds on which many of the species are found. Their gills are often in a form of feathery plumes on their backs which gives rise to their other name, nudibranchs. Nudibranchs with smooth or warty backs have no visible gill mechanisms and respiration may take place directly through the skin. A few of the sea slugs are herbivores and some are carnivores. Many have distinct dietary preferences and regularly occur in association with certain species.

Table of contents
1 Taxonomy
2 Reference
3 External links

Taxonomy

The taxonomy of the Gastropoda is under constant revision, but more and more the old taxonomy is being abandoned. Nevertheless terms as 'opisthobranch' and 'prosobranch' are still being used in a descriptive way (and no longer as taxons). In a sense, we can speak of a taxonomic jungle when we go down to the lower taxonomic levels. The taxonomy of the Gastropoda can be different from author to author. But with the arrival of DNA-sequencing, a more definite taxonomy of the higher taxonomic levels is to be expected in the near future.

Till recently there were four subclasses. :

According to the newest insights (Ponder & Lindberg, 1997), the taxonomy of the Gastropoda should be rewritten. According to these authors, taxa can only be valid when defined in cladistic terms. In their opinion, a classification with a rigid set of hierarchical levels is not necessary or even desirable. Their thorough morphological analysis led to several cladistic trees, producing a single cladistic tree. The authors then provided names for the clades in this tree. Integrating their findings into a working taxonomy will be a true challenge in the coming years. At present, it is impossible to give a classification of the Gastropoda that has consistent ranks and also reflects current usage. Next is a proposed classification, down to the level of superfamily.

Class Gastropoda ( Cuvier, 1797)

Subclass Eogastropoda (Ponder & Lindberg, 1996) (earlier: Prosobranchia)

Subclass Orthogastropoda Ponder & Lindberg, 1996 (earlier Prosobranchia, Opisthobranchia)

Superorder Cocculiniformia Haszprunar, 1987

Superorder ‘Hot Vent Taxa' Ponder & Lindberg, 1997 Superorder Vetigastropoda Salvini-Plawen, 1989 (limpets) Superorder Neritaemorphi Koken, 1896 Superorder Caenogastropoda Cox, 1960 Superorder Heterobranchia J.E. Gray, 1840 Other classes of the Mollusca are : Bivalvia, Scaphopoda, Aplacophora, Polyplacophora, Monoplacophora, Cephalopoda

Reference

External links