Fore gill slugs

The division of living beings into systematics is a continuous subject of research. Different systematic classifications exist side by side and one after the other. The taxon treated here has become obsolete due to new research or is not part of the group systematics presented in the German-language Wikipedia.

Panel Prosobranchia from Art Forms of Nature by Ernst Haeckel (1904)

Foregill snails ( Prosobranchia , Streptoneura ) is a subclass that was used in the snail taxonomy until the 1990s . It corresponded to a morphological division of the snails according to the type of respiratory organs into fore gills, hind gills and lung snails . The taxon is since the taxonomy of Ponder & Lindberg (1997) no longer used because the subclass as paraphyletisch no longer meets it turned and modern phylogenetic systematics.

characterization

The main criterion for belonging to the Prosobranchia is that the gills are in front of the heart when viewed from the head. Another feature is the original presence of a housing that can be closed with a horny or chalky lid ( operculum ).

There are marine species, freshwater snails, and some land-based species among these snails.

etymology

Prosobranchia "Vorderkiemer" can be derived from the ancient Greek : πρωρ- "front-", βράγχιον ( ngr. Βράγχιο) "gill" (cf. βραχίων "arm", "branch"). Prosobranchia literally means "front (lying in front) gills".

Streptoneura “Verdehtnervige” can be derived from the ancient Greek: στρεπτός (also στρεβλός) “twisted”, “twisted”, from στρέφω (also στρεβλόω) “twist”, “wind”; νεῦρον "tendon", "(fine) thread", "nerve" (hence also neuron and as cognate ngr. νεύρο "nerve"). Streptoneura literally means "twisted nerves". Euthyneura "straight nerves" - the name of the hind gill and pulmonary snails - is derived from the adjective ευθύς "straight", so literally means "straight nerves".

Evolution of the taxon

Systematics . Classifications of living beings and systematics have appeared since the 17th and 18th centuries. They have an inherent desire to categorize animals according to characteristics and ancestry. For a long time, morphological systematics were used that are based on the functional structure of animals and can also be implemented with simple means. In these cases, closeness to ancestry is concluded from the similarity in structure. This approach is justifiable on a large scale (e.g. when differentiating between trout, turtle, and giraffe), since evolutionary developments take place over long periods of time and have a memory (e.g. a caiman liver will not develop from a leopard liver). However, it can fail in fine-tuning (e.g. the Asian elephant is more closely related to the extinct Maltese dwarf elephant than to the African elephant). With modern methods of genetic engineering, however, biologists have the technical means to work out kinship relationships more precisely. An exact ancestry is not only interesting in and of itself, but also allows the influence of changes in the environment on developments to be worked out.

Classic approaches . The introduction

Great gastropoda
- Subclass Prosobranchia
- Subclass Opisthobranchia
- Subclass Pulmonata

goes back to H. Milnes Edwards (1848). The dominant criterion here is the type of respiratory organs in the snail. In the recent (today's) species of Prosobranchia, a right torsion of the abdomen by 180 ° towards the head took place in evolution. As a result, as seen from the head, the position of the internal organs has changed, especially the internal gills in front of the heart. In the evolution of the species of Opisthobranchia, the right torsion was corrected by a detorsion of the abdomen by −90 °. As a result, the internal organs of the hind gills are positioned so that their gills are behind the heart when viewed from the head. The pulmonates, which cover the rest of the snails, no longer have gills, but in the course of evolution and land acquisition, the gills in their mantle cavity have been transformed into lungs.

With the system of J. Thiele (1929–1935)

this classification became too

Great gastropoda
- Subclass Prosobranchia / Streptoneura
- Euthyneura group
  - Subclass Opisthobranchia
  - Subclass Pulmonata

refined. The reason for this is that the paired cord nerves crossed with the right torsion by 180 °, and that the crossover was canceled again with the detorsion. In this respect, the morphological property of crossed nerve tracts offers a criterion for dividing the snails into the groups of Streptoneura and Euthyneura . If the type of respiratory organs is also stored as a secondary criterion, the above three-way division results; the Prosobranchia subclass and the Streptoneura group overlap.

Modern approaches . With modern phylogenetic analyzes, Ponder & Lindberg showed in the 1990s that the prosobranchia is a paraphyletic subclass. I.e. in the taxometric subtree of the species of the Prosobranchia there are species that do not come from the same lineage. However, since this contradicts a primary goal of systematics, a new systematics became necessary. This was provided by Ponder & Lindberg (1996) with the division of the snails into two subclasses:

Great gastropoda
- Subclass Eogastropoda
- Subclass Orthogastropoda

The Eogastropoda ("early snails") contained the historically older snail models in the superfamilies Euomphalida (de Koninck, 1881) and Patellogastropoda (real limpets, Lindberg, 1986). The Prosobranchia subclass was then neatly divided, so that the resulting systematics by Ponder & Lindberg (1997) became monophyletic based on what was known at the time .

Systematics

The embedding of the prosobranchia in the systematics before Ponder & Lindberg (1997):

Class Gastropoda - pelvis
- Subclass Prosobranchia - Fore gill
  - Order Archaeogastropoda - adult snails
  - Order Mesogastropoda - middle snails

Web links

Commons : Mattheus Marinus Schepman: The Prosobranchia of the Siboga Expedition Part I: Rhipidoglossa and Docoglossa - Collection of images, videos and audio files

Individual evidence

↑ Thiele, J. (1929-1935): Handbook of systematic molluscology. 2 volumes. 1-1154.
^ R. Bieler & PM Mikkelsen (Sci.Ed.); JS Bhatti (Transl.); J. Thiele : Handbook of systematic molluscology. English: Handbook of systematic malacology. Publ: Washington, DC; Smithsonian Institution Libraries; National Science Foundation; 1992-. Content: pt. 1. Loricata; Gastropoda: Prosobranchia - pt. 2. Gastropoda: Opisthobranchia and Pulmonata - pt. 3. Scaphopoda / Bivalvia / Cehalopoda - pt. 4. Comparative Morphology / Phylogeny / Geographical Distribution. OCLC 680545970 .
^ Winston F. Ponder and David R. Lindberg : Towards a phylogeny of gastropod molluscs: an analysis using morphological characters ; In: Zoological Journal of the Linnean Society. Volume 119, No. 2, 1997, pp. 83-265; doi : 10.1111 / j.1096-3642.1997.tb00137.x .

[Thiele1-1] Thiele, J. (1929-1935): Handbook of systematic molluscology. 2 volumes. 1-1154.

[Thiele2-2] R. Bieler & PM Mikkelsen (Sci.Ed.); JS Bhatti (Transl.); J. Thiele : Handbook of systematic molluscology. English: Handbook of systematic malacology. Publ: Washington, DC; Smithsonian Institution Libraries; National Science Foundation; 1992-. Content: pt. 1. Loricata; Gastropoda: Prosobranchia - pt. 2. Gastropoda: Opisthobranchia and Pulmonata - pt. 3. Scaphopoda / Bivalvia / Cehalopoda - pt. 4. Comparative Morphology / Phylogeny / Geographical Distribution. OCLC 680545970 .

[SPL-3] Winston F. Ponder and David R. Lindberg : Towards a phylogeny of gastropod molluscs: an analysis using morphological characters ; In: Zoological Journal of the Linnean Society. Volume 119, No. 2, 1997, pp. 83-265; doi : 10.1111 / j.1096-3642.1997.tb00137.x .