Tubefoot
| Tubefoot | ||||||||||||
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Antalis vulgaris |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Scaphopoda | ||||||||||||
| Bronn , 1862 | ||||||||||||
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The Scaphopods or Grabfüßer (Scaphopoda) are a group of molluscs and the subgroup conchifera (Conchifera) with about 500 extant species. They live in the mud of the seabed buried and can accommodate up to a water depth of 7000 meters occur. Over 900 species are described from the fossil record ; how many of them are valid species has not yet been researched. The oldest scapula are known from the Devonian , although this evidence has recently been disputed. There are undisputed scotties from the Triassic . Fossil barefoots have mainly been confused with tube worms, tubular mussels, sea urchin spines and elongated cephalopods (and vice versa), hence the uncertainty about the first occurrence and the total number of fossil species.
Blueprint
The housing of the animals is tubular, elongated and open at both ends. The animal, whose coat has grown together with the housing, is in this housing. In the order Dentalida, the case is reminiscent of a miniature version of an elephant's tusk (except that it is hollow and open at both ends). This is where the colloquial term elephant's tooth comes from . The rear opening is constantly enlarged as it grows, but can also be narrowed again in the adult stage by a plug (callus) or a secondary tube. Within the order of the Gadilida the mouth narrows again in the adult stage; the case can be inflated in the middle or near the front opening. The surface of the bowl is often decorated with vertical and horizontal stripes and color patterns.
The muscular grave foot with various attachments ends at the larger opening of the shell. There is no separate head, only a mouth pit with a small radula with few elements and jaw-like structures. Long, stretchable threads (captacula) with a thickened end arise here. These catch threads are used to track down the prey, mainly foraminifera and other small organisms in the sediment gap system. The prey is stuck to the ends by a secretion, pulled to the oral cavity and crushed with the radula. Movement takes place by stretching out and anchoring the foot in the sediment. The body and housing are then retightened. Eyes are absent; they are not necessary in the digging way of life and have been reduced to the basic structure of the molluscs.
The upper opening of the housing protrudes over the sediment surface or at least into the oxygen-containing area of the surface sediment. Fine hairs in the mantle cavity ensure a flow of water into the mantle cavity; rapid contraction of the soft body forces the wastewater out of the mantle cavity. As a result, not only are the excretory products transported out of the mantle cavity, but also the sex products, the gametes (eggs and seeds) of the separated-sex animals are released into the open water, where fertilization takes place. The development takes place via relatively yolk-rich eggs and a special larva. After the larva has spent some time in the plankton, it goes on to life on the ground and develops into a scot-pod.
The housing consists of the lime modification aragonite and is usually made up of three layers: an inner, secondary prismatic layer, a middle cross-lamella layer and an outer prismatic layer.
Phylogeny
In most of the classifications of molluscs, the barefoot is considered to be the sister group of the mussels . However, in the fossil record there is a group of molluscs, the beaked shawl (Rostroconchia), which could have been the ancestors of the puntipods. Consequently, in classifications that include the fossil groups, the scabbards are only interpreted as the order of the beaked scarf. More recently, based on genetic data, some authors have also favored a sister group ratio of cephalopods and scotopods. However, this idea contradicts the morphological data, especially the embryogenesis and especially the large stratigraphic gap between the first appearance of the cephalopods (Upper Cambrian) and the barnacles (Devonian? Or even later).
Examples
The two species Antalis vulgaris and Antalis entalis, found in the North Sea, and the species Dentalium elephantinum living in the Indo-Pacific , all of which belong to the family Dentaliidae in the order Dentaliida, belong to the first described species of the scottish .
literature
- Engeser, Theo & Frank Riedel 1996. The evolution of the Scaphopoda and its implications for the systematics of the Rostroconchia (Mollusca). Messages from the Geological-Paleontological Institute of the University of Hamburg, 79: 117–138.
- Peel, John 2004. Pinnocaris and the origin of scaphopods. Acta palaeontologica polonica, 49: 543-550.
- Pojeta, John & Bruce Runnegar 1976. The paleontology of the rostrochonch molluscs and the early history of the Phylum Mollusca. US Geological Survey Professional Paper 968: 1-88.
- Steiner, Gerhard & H. Dreyer 2003. Molecular phylogeny of Scaphopoda (Mollusca) inferred from 18S rDNA sequences: support for a Scaphopoda-Cephalopoda clade. Zoologica Scripta 32 (4): 343-356.
- Waller, TR 1998, Origin of the Molluscan Class Bivalvia and a Phylogeny of Major Groups; In: An Eon of Evolution; Paleobiological Studies Honoring Norman D. Newell, ed. by PA Johnston & JW Haggart, University of Calgary Press, pp. 1-45.
- Otto Grunert : The Scaphopods and Gastropods of the German Triassic . Erlangen: A. Vollrath, 1898, Archives
