Palaeoheterodonta

Neotrigonia margaritacea

The Palaeoheterodonta are a large group of mussels ( Bivalvia ), which is conducted in the newer classifications as an order within the Autolamellibranchiata. There is a small shell group includes the so-called " freshwater mussels " and the old-fashioned acting Trigonioida. The Palaeoheterodonta are considered the sister group of the Heterodonta. The first shells, which can be attributed to this group will appear in the Lower Ordovician.

Characterization

The housing of the Palaeoheterodonta are usually equivalve; aberrant forms are rare. The shells are aragonitisch with three mineralized layers: an inner and middle pearl ply and an outer prismatic layer, which is then overlaid with the organic periostracum. The castle was originally heterodont or schizodont, but can also be reduced. The ligament is external. The Palaeoheterodonta almost all isomyar, ie the two sphincters are approximately equal. The gills are filibranch or eulamellibranchiat.

Way of life

The Palaeoheterodonta are predominantly living in fresh water mussels ( order Unionoida ); but also marine forms occur ( Trigonioida ). Most species feed on "Shell - typical " as filter feeders, which are buried in the sediment in whole or in part, or lie on the sediment. A few forms are also firmly cemented.

System

The Palaeoheterodonta be considered in cladistics as the sister group of the Heterodonta. Both superorders be summarized in many classifications to a higher-level taxon Heteroconchia. In most classifications the taxon is attributed to two orders of dissent, which are considered in the phylogenetic systematics as be sister.

Superorder Palaeoheterodonta Newell, 1965

  • Order Trigonioida Dall, 1889 Superfamily Trigonioidea Lamarck, 1819
  • Superfamily freshwater mussel similar ( Unionoidea Rafinesque, 1820 )
  • Superfamily Etherioidea Deshayes, 1830
  • Superfamily † Archanodontoidea Weir, 1969
  • Superfamily † Anthracosioidea Amalitsky, 1892
  • Superfamily Cycloconchoidea Ulrich, 1884
  • Superfamily Babinkoidea Horny, 1960
  • Superfamily Glyptarcoidea Cope, 1996
  • Superfamily † Modiomorphoidea Miller, 1877
  • Superfamily † Kalenteroidea Marwick, 1953
Norman D. Newell
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