Stomochord

The stomochord is a flexible, hollow tube found in hemichordates. Stomochords arise in embryonic development as an outpocketing from the roof of the embryonic gut anterior to the pharynx. In adults, they extend dorsally from the pharynx into the proboscis, and serve to communicate with the oral cavity. Their walls are composed primarily of epithelial cells, but ciliated and glandular cells are also present.[1]

Relationship to chordate anatomy

Stomochords were initially considered a variant of a primitive notochord, a defining feature of chordates. However, they are now recognized to not share histological composition to that of the notochord found in chordates, lacking the fibrous sheath characteristic of a notochord.[1]

In addition, gene expression studies have failed to provide any evidence for homology between the notochord and the stomochord, or between the notochord and any hemichordate structure. The Brachyury (T) gene, which is expressed in the ascidian notochord, is not expressed in the stomochord, and collagen is absent.[2]

gollark: I can upload some memes from my library?
gollark: Besides, we've had the majority of gods in active containment since 1996.
gollark: They should be. Religion mostly deals with unfalsifiable vague claims and "faith", which is basically the opposite of empiricism.
gollark: Declining religion.
gollark: Sure. Although it's still hard to distinguish whether that's a "science" thing or a "weird societal factors" thing.

References
  1. Kardong, Kenneth V. (1995). Vertebrates: comparative anatomy, function, evolution. McGraw-Hill. pp. 55, 57. ISBN 0-697-21991-7.
  2. Moody, Sally A. (2007). Principles of Developmental Genetics. Elsevier. ISBN 978-0-12-369548-2.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.