Everything about Hemichordate totally explained
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.
Further Information
Get more info on 'Hemichordate'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://hemichordata.totallyexplained.com">Hemichordata Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
