Prosobranchia

Prosobranch ( Prosobranchia, Streptoneura ) is a sub-class, which was used until the 1990s in the taxonomy of the worm. It corresponded to a morphological classification of snails on the nature of the respiratory organs in prosobranch, and opisthobranch gastropods. This taxon has not been used since the taxonomy of Ponder & Lindberg (1997 ), since the subclass no longer meets as paraphyletic and modern phylogenetic systematics turned out.

Characterization

The main criterion for belonging to the Prosobranchia is viewed from the head that the gills are the heart. Another feature is the original presence of a casing with a horny or calcareous operculum (operculum ) may be closed.

There are among these snails marine species, freshwater snails and some live in the country representatives.

Etymology

Prosobranchia can be derived from the Ancient Greek: πρωρ - = - front; βραχίων = arm, branch; gr βράγχιο = gill. Prosobranchia literally means thus leading branches ( gills).

Streptneura can be derived from the Ancient Greek: στρεβλός = twisted, στρεβλόω = rotate, wind; νευρο - = tendon, ( fine ) thread. Streptoneura literally means so twisted tendons.

Development of the taxon

Systematics. Classifications of living things and classifications occur since the 17th, 18th century. You is inherent in the desire to categorize the animals according to characteristics and ancestry. For a long time morphological classifications have been used which are based on the functional structure of animals and can be realized with simple means. These descent near is inferred from similarity in structure. This approach is on a large scale (eg in distinguishing trout, turtle, giraffe) justifiable, as evolutionary developments over long periods of time to go and have a memory (eg, will evolve from a Leopard liver no Cayman liver). However, it may fail in the fine determination (eg, the Asian elephant closer to the extinct dwarf elephant Maltese used as the African Elephant). With modern methods of genetic engineering, however, biologists have technical means at hand to work out relationships in more detail. A detailed derivation is not only in itself interesting, but it also allows, work out the effect of changes in the environment on development.

Classical approaches. The classification

• Class Gastropoda Subclass Prosobranchia
• Subclass Opisthobranchia
• Subclass Pulmonata

Goes back to H. Milne Edwards ( 1848). The dominant criterion here is the nature of the respiratory organs of the screw. In the recent ( today ) Types of Prosobranchia found in the evolution of a Rechtstorsion abdomen 180 degrees towards the head instead. This has, viewed from the head, changed the position of the internal organs, are particularly the inner gills in front of the heart. For species of Opisthobranchia a correction of Rechtstorsion by detorsion of the abdomen at -90 ° took place in evolution. Thus, the internal organs of opisthobranch are so viewed from the head that their gills are back behind the heart. The Pulmonata, which cover the rest of the slugs, now have no gills, but in the course of evolution and acquisition of land formed in its mantle cavity, the gills to lungs to.

With the scheme of J. Thiele (1929-1935), this classification was to

• Class Gastropoda Subclass Prosobranchia / Streptoneura
• Group Euthyneura Subclass Opisthobranchia
• Subclass Pulmonata

Refined. The reason for this is that when the Rechtstorsion 180 ° crossed the paired strand nerves, and that the crossing was canceled at the Detorsion again. Therefore gives the morphological characteristic crossed Nervenbahnenein criterion to split the worm in the groups of Streptoneura and Euthyneura. Is stored as the secondary criterion nor by the nature of the respiratory organs, the result above trichotomy; the subclass Prosobranchia and the group Streptoneura overlap.

Modern approaches. With modern phylogenetic analyzes showed Ponder & Lindberg now in the 1990s that the Prosobranchia is a paraphyletic subclass. That in taxometrischen subtree of the types of Prosobranchia occur in ways that do not come from the same lineage. However, since that contradicts a primary goal of systematics, a new system was necessary. This was supplied by Ponder & Lindberg (1996 ) with the division of the worm into two subclasses:

• Class Gastropoda Subclass Eogastropoda
• Subclass Othrogastropoda

The Eogastropoda ( "early worm " ) contained the evolutionarily older worm models in the superfamilies Euomphalida ( de Koninck, 1881) and Patellogastropoda (true limpets, Lindberg, 1986). The subclass Prosobranchia was then split clean, so that the resulting taxonomy of Ponder & Lindberg (1997 ) to damaligem knowledge was monophyletic.

System

The embedding of Prosobranchia in the scheme before Ponder & Lindberg (1997):

• Class Gastropoda - Bauchfüßer Subclass Prosobranchia - prosobranch Order Archaeogastropoda - Altschnecken
• Order Mesogastropoda - means snails
• Order Neogastropoda - Neuschnecken
• Order Allogastropoda