Mesogastropoda
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The Mesogastropoda used to be an order of prosobranch gastropods (i.e. with the gills situated in front of the heart) in the taxonomy of J. Thiele (1921). The name ‘Mesogastropoda’ no longer is considered a taxon. It can only be used in descriptive way. It is now included in a monophyletic clade, the superorder Caenogastropoda Cox, 1960. Therefore there is no taxobox present in this article. A more detailed account of the taxonomy is given in Gastropoda and Archaeogastropoda.
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Description
There are about 30,000 species. Most are to be found in the sea, but there are also numerous species in freshwater and even a few occur on land. Their shells lack mother-of-pearl.
Most are herbivorous, but a few are parasites or predators. The radula have seven denticles (= teeth), sometimes reduced.
The Mesogastropoda are, in many ways, already more developed than the Archaeogastropoda. Through torsion of the intestinal mass and a spiral movement of the body, the gill, the kidney and the osphradium (= sensory receptor, olfactory organ) have disappeared on the right side. They all reside on the left side.
The heart consists of only one atrium and one ventricle. The nervous system is also progressively more developed. The ganglia are connected with different organs through nerve pathways. In the Mesogastropoda, the execretory and the reproductive ducts are separated (in contrast with the most primitive prosobranchs). Many members produce egg capsules, containing one to more than 1,000 eggs.
Taxonomy
of the Mesogastropoda (according to ITIS) (no longer in use). The current taxonomy (according to Ponder & Lindberg, 1997) is given under Gastropoda
- Family Abyssochrysidae
- Family Aciculidae
- Family Aporrhaidae Morch, 1852
- Family Asterophilidae
- Family Cassididae Swainson, 1832
- Family Chondropomidae
- Family Choristidae
- Family Cingulopsidae
- Family Cochlostomatidae
- Family Cymatiidae Iredale, 1913
- Family Diastomidae Cossman, 1895
- Family Eratoidae
- Family Fossaridae Trachel, 1861
- Family Hydrococcidae
- Family Iravadiidae
- Family Lacunidae Gill, 1871
- Family Melanopsidae
- Family Micromelaniidae
- Family Omalaxidae
- Family Paedophoropodidae
- Family Pilidae
- Family Pomatiopsidae
- Family Pseudosacculidae
- Family Stenothyridae
- Family Stiliferidae
- Family Struthiolariidae
- Family Syrnolopsidae
- Family Trachysmidae
- Family Trichotropidae Gray, 1850
- Family Trochaclisidae
- Superfamily Cyclophoroidea
- Superfamily Heteropoda Lamarck, 1901
- Superfamily Viviparoidea
Reference
Thiele, J., 1929-1935. Handbuch der Systematischen Weichtierkunde. 2 vols. 1154 p., 584 figs
External link
Classification of Gastropoda (http://www.amonline.net.au/invertebrates/mal/ponder_classific2.htm)