Carpoidea
| Carpoidea | ||||||||||
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Cothurnocystis , on the left the articulated appendage, on the right below, between the two horn-like protrusions of the body disc , a body opening, presumably the anus . The mouth is probably at the base of the appendage. |
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| Temporal occurrence | ||||||||||
| Middle Cambrian to Devonian | ||||||||||
| 513 to 388.1 million years | ||||||||||
| Locations | ||||||||||
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| Systematics | ||||||||||
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| Scientific name | ||||||||||
| Carpoidea | ||||||||||
| Jaekel , 1918 |
The Carpoidea , also called Homalozoa or Calcichordata , are an extinct class of echinoderms . They are among the oldest echinoderms and have been recorded in fossil records since the Middle Cambrian and became extinct in the Devonian . A total of about 60 genera have been described.
features
Carpoids are strangely asymmetrical and show neither the two-sided symmetry ( bilateria ) that is typical for most animal groups nor the five axes of symmetry ( pentamerism ) inherent in echinoderms . They usually have an irregularly lobed, circular, heart-shaped or pear-shaped body disc (theka) and one or two long, articulated body processes that are interpreted as a grasping organ analogous to the arms of sea or brittle stars or, alternatively, as a tail. The theka was one to five centimeters long and had a flat and a curved side. The flat one is interpreted as the bottom, the arched one as the top. The theka was armored by calcite plates , large (marginalia) sat on the sides, small (centralia) above and below. They were arranged like a mosaic or overlapped like roof tiles so that the theca could expand and contract. The body processes were the length of the theca or longer. Whether an ambulacral system existed is controversial.
Systematics
The Carpoidea are presumably a collective group of original echinoderms that arose in an early radiation before the formation of the pentameric symmetry of the echinoderms. So they do not form a monophylum . The family relationships are controversial.
A small group of scientists suspected the ancestors of the chordates (Chordata) in the Stylophora, a group of the Carpoidea . You see a tail in the articulated appendage of the body and the head in the bar. The body opening opposite the tail is interpreted as a mouth, pore-like openings on both sides of the body appendage are interpreted as gills . This hypothesis , known as the calcichordata theory , met with a lot of contradiction, among other things because chordate-like species that are older than the stylophora have been found in the Chinese Chengjiang fauna community .
Sub-taxa
- Ctenocystoidea (Middle Cambrian)
- Soluta (Homostelea) (middle Cambrian to Devonian)
- Cincta ( Homoiostelea ) (Middle Cambrian)
- Stylophora (Middle Cambrian to Middle Ordovician)
literature
- Bernhard Ziegler: Introduction to Paleobiology, Part 3, Special Paleontology, Worms, Arthropods, Lophophorates, Echinoderms . Stuttgart: Schweizerbartsche Verlagbuchhandlung, 1998, ISBN 3-510-65179-0