Anomalodesmata

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Anomalodesmata
Thracia convexa

Thracia convexa

Systematics
Trunk : Molluscs (mollusca)
Sub-stem : Shell molluscs (Conchifera)
Class : Mussels (Bivalvia)
Subclass : Autolamellibranchiata
Superordinate : Anomalodesmata
Scientific name
Anomalodesmata
Dall , 1889

The anomalodesmata are a large group of mussels (bivalvia), which in the newer classifications is listed as an order or superordinate order within the autolamellibranchiata . It is a large, very diverse group of mussels found in many habitats.

characterization

The housings of most anomalodesmata are, as adopted from the basic plan of the mussels, equal. However, among the younger groups there is a tendency towards weak to strong inequality of the two valves. Most anomalodesmata have no teeth in the lock; H. the teeth are largely reduced. Other groups have simple teeth, but they are secondary. The ligament is originally external, but in the case of derived forms it can also be semi-internal or internal in a so-called lithodesma or chondrophor . However, chondrophores seem to have arisen several times independently of one another. In some groups the ligament is even completely reduced. The shells of all representatives of the anomalodesmata are aragonitic, and most of them have a prismatic-mother-of-pearl microstructure (mother-of-pearl inside, prismatic layer outside), which is covered by the organic periostracum. A few groups have independently developed homogeneous shell structures. Another typical feature of the anomalodesmata are spicules on the shell surface, which are anchored in the periostracum. They are produced in the mantle before they are then built into the periostracum . The spicula are often arranged in rows and probably serve for better anchoring in the sediment. The vast majority of anomalodesmata are isomyaric; H. the two sphincters are approximately the same size, only a few forms are anisomyar. The foot is usually well developed, the siphons can be quite large in digging forms. The gills are eulamellibranchiat in the majority of the groups. Only a smaller group (septibranchia) has transformed the gills into a septum.

Way of life

The anomalodesmata are exclusively marine mussels. Occasional reports from representatives living in freshwater have proven to be in error. Today's representatives of the anomalodesmata occur from the intertidal areas to the deep sea. And even within this depth range they have developed a broad spectrum of habitats, from digging in soft sediments of different depths to drilling hard substrates or attaching them to hard substrates using a byssus or cementing. Most species feed on "mussel-typical" filter feeders. There are also some forms that, very unusual for mussels, predatory feed on small crustaceans.

Systematics

The anomalodesmata are listed in most of the older classifications as a superordinate or even a subclass of mussels. According to the more recent studies by Harper et al. (2006), however, this is not justified. The anomalodesmata are therefore only regarded by these authors as an order. However, the anomalodesmata contain two easily distinguishable groups: the Septibranchia Pelseneer, 1889, and the families that were previously grouped together in the order Pholadomyoida. Here, the subdivision of the MolluscaBase is essentially followed, which, however, does not include the orders Pholadomyoida and Septibranchia.

supporting documents

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.
  • Elisabeth M. Harper, Hermann Dreyer & Gerhard Steiner: Reconstructing the Anomalodesmata (Molluusca: Bivalvia): morphology and molecules . Zoological Journal of the Linnean Society, 148: 395-420, London 2006

Individual evidence

  1. ↑ MolluscaBase: Anomalodesmata