Helicoplacoidea
| Helicoplacoidea | ||||||||||
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| Temporal occurrence | ||||||||||
| Lower Cambrian | ||||||||||
| 530 to 516 million years | ||||||||||
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| Systematics | ||||||||||
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| Scientific name | ||||||||||
| Helicoplacoidea | ||||||||||
| Durham & Caster , 1963 | ||||||||||
The Helicoplacoidea are an extinct class of echinoderms from the Lower Cambrian of western North America. Together with the Carpoidea , the Edrioasteroidea and the Eocrinoidea , they are among the oldest fossilized echinoderms.
features
The helicoplaoids were small, asymmetrical, spindle-shaped organisms . They reached a length of 2 to 5 centimeters and a diameter of one to two centimeters. Its surface was covered with spiral, rectangular skin plates that could be thorny. They were likely held together by a subcutaneous tissue and could be pushed under each other when the animal contracted.
The ambulacral groove , which began at the upper or front pole, probably the location of the mouth, and ended at the opposite pole, was also arranged in a spiral . A secondary ambulacral channel branches off from the main ambulacral channel. Some scientists suspect the mouth is not at the upper pole, but at the branching point of the two ambulacral channels.
Tentacles or other body appendages cannot be detected.
Way of life
It is usually assumed that the helicoplaoids lived upright, with their lower end stuck in the mud or sand, and fed as suspension eaters. Alternatively, the helicoplaoids could have lived flat on or in the sediment, crawled like earthworms and picked up sediment particles and utilized organic components.
Genera
literature
- Bernhard Ziegler: Introduction to Paleobiology. Part 3: Special paleontology, worms, arthropods, lophophorates, echinoderms. Schweizerbartsche Verlagbuchhandlung, Stuttgart 1998, ISBN 3-510-65179-0 .
Web links
- The Paleobiology Database: Helicoplacoidea