Dreissenidae
Zebra mussel ( Dreissena polymorpha )
The zebra mussels ( Dreissenidae ) are a family of molluscs from the order of the Veneroida. It is the only family of the superfamily Dreissenoidea.
Features
The housings are small to medium in size. You are mussel -shaped ( mytiliform ), horse mussel -shaped ( modioliform ) or rounded triangular. The vortex ( umbo ) is marginal or very close to the edge. A umbonales septum is present, but may be rudimentary. The castle is toothless and the sphincters are unequal in size ( heteromyar ), the front sphincter is attached to the septum. The gills belong to eulamellibranchiaten type. The shell is composed of aragonite. In cross-section, it consists of an inner layer of the complex cross slats and an outer layer of simple discs and cross slats. The larvae are free-swimming, the adult animals they are attached by a byssus threads to the substrate.
Dissemination
Since the Eocene Ypresium - level representatives of the family found in Europe and Asia Minor in the east to Kazakhstan ( Aral Sea ). From the late Oligocene then also occur in central and tropical South America, from where they spread out during the Neogene to North America.
Introduced species are found in India, Hong Kong and Japan, probably in the Fiji Islands and West Africa. This originally from North America kind Mytilopsis leucophaeata coming today including in the North Sea-Baltic Canal before, but also in the Black Sea, where it displaces other mussel species. The zebra mussel ( Dreissena polymorpha ) and the quagga zebra mussel ( Dreissena rostriformis bugensis ) are originally from the Ponto - Caspian region and act as invasive species in Europe and North America.
Congeria are index fossils of the Pannon whose deposits from the tectonic subsidence area between the Alps and the Carpathians are known.
System
Molecular genetic studies showed that zebra mussels are the sister taxon of a clade from the Myidae and Corbulidae, to further use are beyond the Pholadidae and shipworms.
The family includes two subfamilies, one of which ( Dreisseninae ) comprises the three extant genera Dreissenomyinae only two known fossil genera ( species selection):
- Subfamily Dreisseninae Dreissena Dreissena polymorpha, the zebra mussel
- Dreissena rostriformis Dreissena rostriformis rostriformis
- Dreissena rostriformis bugensis, the Quagga - Zebra Mussel
- Congeria kusceri
- Mytilopsis leucophaeata, the brackish water clam triangle
- Subfamily Dreissenomyinae Dreissenomya †
- Sinucongeria †
A first molecular genetic study of the internal systematics of the Recent genera pointed out that Congeria and Mytilopsis be sister and form a clade, which faces Dreissena.