Hemichordate: Difference between revisions
robot Erbij: zea:Hemichordata |
No edit summary |
||
| Line 16: | Line 16: | ||
}} |
}} |
||
'''Hemichordata''' is a [[Phylum (biology)|phylum]] of worm-shaped marine [[deuterostome]] [[animal]]s, generally considered the sister group of the [[echinoderm]]s. They date back to the Lower or Middle [[Cambrian]] and include an important class of [[fossil]]s called [[graptolite]]s, most of which became extinct in the [[Carboniferous]]. They seem to have a primitive form of [[notochord]], but this is most likely the result of [[convergent evolution]]. A hollow neural tube exists among some species (at least in early life), probably a primitive trait they share with the common ancestor of [[chordata]] and the rest of the deuterostomes. |
'''Hemichordata''' is a [[Phylum (biology)|phylum]] of worm-shaped marine [[deuterostome]] [[animal]]s, generally considered the sister group of the [[echinoderm]]s. They date back to the Lower or Middle [[Cambrian]] and include an important class of [[fossil]]s called [[graptolite]]s, most of which became extinct in the [[Carboniferous]]. They seem to have a primitive form of [[notochord]], formed from a diverticulum of the foregut called a [[stomochord]], but this is most likely the result of [[convergent evolution]]. A hollow neural tube exists among some species (at least in early life), probably a primitive trait they share with the common ancestor of [[chordata]] and the rest of the deuterostomes. |
||
The Body of Hemichordates are divided into three parts, proboscis, collar and trunk. They have open circulatory systems also complete digestive tract but the musculature in their gut is very poorly developed, and food is mostly transported through it by using the [[Cilium|cilia]] that cover its inside surface. |
The Body of Hemichordates are divided into three parts, proboscis, collar and trunk. They have open circulatory systems also complete digestive tract but the musculature in their gut is very poorly developed, and food is mostly transported through it by using the [[Cilium|cilia]] that cover its inside surface. |
||
| Line 25: | Line 25: | ||
* [https://www.webdepot.umontreal.ca/Usagers/cameroc/MonDepotPublic/Cameron/Species.html Cameron, C. B. ''Classification of the extant hemichordata''] |
* [https://www.webdepot.umontreal.ca/Usagers/cameroc/MonDepotPublic/Cameron/Species.html Cameron, C. B. ''Classification of the extant hemichordata''] |
||
* [http://tolweb.org/tree?group=Hemichordata&contgroup=Deuterostomia At the Tree of Life] |
* [http://tolweb.org/tree?group=Hemichordata&contgroup=Deuterostomia At the Tree of Life] |
||
* Ruppert. Invertebrate Zoology, seventh ed. |
|||
[[Category:Hemichordates| ]] |
[[Category:Hemichordates| ]] |
||
Revision as of 13:09, 17 December 2007
| Hemichordata | |
|---|---|
| Scientific classification | |
| Kingdom: | |
| Subkingdom: | |
| Superphylum: | |
| Phylum: | Hemichordata Bateson, 1885
|
| Classes | |
Hemichordata is a phylum of worm-shaped marine deuterostome animals, generally considered the sister group of the echinoderms. They date back to the Lower or Middle Cambrian and include an important class of fossils called graptolites, most of which became extinct in the Carboniferous. They seem to have a primitive form of notochord, formed from a diverticulum of the foregut called a stomochord, but this is most likely the result of convergent evolution. A hollow neural tube exists among some species (at least in early life), probably a primitive trait they share with the common ancestor of chordata and the rest of the deuterostomes.
The Body of Hemichordates are divided into three parts, proboscis, collar and trunk. They have open circulatory systems also complete digestive tract but the musculature in their gut is very poorly developed, and food is mostly transported through it by using the cilia that cover its inside surface.
Hemichordata are divided into two classes: the Enteropneusta, commonly called acorn worms, and the Pterobranchia, which may include the graptolites. A third class, Planctosphaeroidea, is proposed based on a single species known only from larvae. The phylum contains about 100 living species. The exact taxonomic position of hemichordata and whether the group is monophyletic is currently under debate. One of the suggestions is that the pterobranchs are more basal deuterostomes, while the enteropneusts are an early offshoot of the lineage who are leading to Chordata.
References
- Cameron, C. B. Classification of the extant hemichordata
- At the Tree of Life
- Ruppert. Invertebrate Zoology, seventh ed.