Palaeoheterodonta
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| Palaeoheterodonta | ||||||||||
| Newell , 1965 |
The palaeoheterodonta are a large group of mussels (bivalvia), which in the newer classifications are listed as a superordinate group within the autolamellibranchiata . It is a small group of mussels that contain the so-called " freshwater mussels " and the ancient-looking Trigoniida . The Palaeoheterodonta are considered to be the sister group of the Heterodonta . The first mussels that can be assigned to this group appear in the Lower Ordovician .
characterization
The housings of the palaeoheterodonta are mostly equilateral; aberrant forms are rare. The shells are aragonitic with three mineralized layers: an inner and middle mother-of-pearl layer and an outer prismatic layer, which is then overlaid by the organic periostracum. The lock is originally heterodont or schizodont, but it can also be reduced. The ligament is external. The palaeoheterodonta are almost all isomyar, i.e. H. the two sphincters are approximately the same size. The gills are filibranch or eulamellibranchiat .
Way of life
The Palaeoheterodonta are mainly freshwater mussels (order Unionida); but also marine forms occur ( Trigoniida ). Most species feed on “mussel-typical” filter feeders that are completely or only partially buried in the sediment, or lie on the sediment. A few shapes are also cemented in place.
Systematics
The palaeoheterodonta are considered in the cladistics as the sister group of the heterodonta. Both superordinate groups are combined in many classifications to form a superordinate taxon Heteroconchia. In most of the classifications, two orders are assigned to the taxon, which are regarded as sister taxa in the phylogenetic system.
Paragraph Palaeoheterodonta Newell , 1965
- Order Trigoniida Dall , 1889
- Superfamily Trigonioidea Lamarck , 1819
- Order Unionida Stoliczka , 1871
- Superfamily Unionoidea Rafinesque , 1820
- Superfamily Etherioidea Deshayes , 1830
- Superfamily † Archanodontoidea Weir, 1969
- Superfamily † Anthracosioidea Amalitsky , 1892
- Order † Actinodontida Douvillé , 1912
- Superfamily Cycloconchoidea Ulrich , 1894
- Superfamily Babinkoidea Horny, 1960
- Superfamily Glyptarcoidea Cope, 1996
- Order † Modiomorpha Newell , 1969
- Superfamily † Modiomorphoidea Miller , 1877
- Superfamily † Kalenteroidea Marwick, 1953
literature
- Michael Amler, Rudolf Fischer & Nicole Rogalla: Mussels . Haeckel library, volume 5. Enke Verlag, Stuttgart 2000 ISBN 3-13-118391-8 .
- Rüdiger Bieler & Paula M. Mikkelsen: Bivalvia - a look at the branches . Zoological Journal of the Linnean Society, 148: 223-235, London 2006.
- Daniel L. Graf & Kevin S. Cummings: Palaeoheterodont diversity (Mollusca: Trigonoida + Unionoida): what we know and what we wish we knew about freshwater mussel evolution. Zoological Journal of the Linnean Society, 148: 343-394, London 2006.