Английская Википедия:Homalozoa
Шаблон:Short description Шаблон:Paraphyletic group
Homalozoa is an obsolete extinct subphylum of Paleozoic era echinoderms, prehistoric marine invertebrates. They are also referred to as carpoids.[1]
Description
The Homalozoa lacked the typical pentamer body form of other echinoderms, but all were sessile animals. Instead all Homalozoans were markedly asymmetric, and were extremely variable in forms.
The body (theca) was covered with calcite plates with a number of openings. Their form is in some cases so unusual that it is unclear which openings are to be considered as mouth and anus. Many of them were stalked, similar to sea lilies (crinoids), but often their bodies were bent over, so that the mouth and anus projected forwards rather than upwards. Some forms, especially stylophorans, rested flat on the sea floor.[2]
In some forms the single ray (brachiole or aulacophore) possessed an ambulacral groove.[3]
It has been claimed that some forms possessed gills and gill slits.[4]
Taxonomy
Homalozoans were traditionally considered to be stem-group echinoderms,[5] but had also been considered to lie in the stem lineage of the chordates (calcichordates). However, it is now generally accepted that homalozoans were echinoderms because their calcite skeleton was composed of the typical stereom crystalline structure.[6]
They include the unusual stylophorans (mitrates and cornutes), Homoiostelea (solutes), the Homostelea (cinctans), and the Ctenocystoidea (ctenoid-bearing homalozoans).[7] They have recently been recognised as a polyphyletic group. The stylophorans are now classified as a clade of the Crinozoa, whereas the other three are classified as clades of the Blastozoa.[7]
Solutes
Unlike many other types of echinoderm, solute homalozoans lack radial symmetry (such as the five limbs of a starfish).[8] [9] Solutes are the sole order of the class Homoiostelea.
Solute fossils have an irregularly shaped flattened body covered in calcite plates, and are up to about 10 cm long. The body has two appendages, interpreted as a "feeding arm" at one end, bearing tube feet at its end, and a "stele" at the other, which may have been used by the animal to propel itself along the sea floor.[10]
See also
References
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite book
- ↑ Шаблон:Cite journal
- ↑ Шаблон:Cite book - pages 401-404
- ↑ Шаблон:Cite web
- ↑ 7,0 7,1 Шаблон:Cite journal
- ↑ A. B. Smith Deuterostome phylogeny and the interpretation of problematic fossil echinoderms, page 543-544 in Thomas Heinzeller, James H. Nebelsick Echinoderms: München, CRC Press, 2004 Шаблон:ISBN,
- ↑ Шаблон:Cite journal
- ↑ Henry Gee Before the backbone: views on the origin of the vertebrates, Springer, 1996 Шаблон:ISBN page 204
