Chordata- John Fountaine
Chordata is the phylum with the most complex nervous system, with focus around the brain, notochord, and spinal chord. These complex creatures are the most diverse of any phylum and Chordata is separated into three sub-phyla, Vertebrata, or the replacement of the notochord by the spinal chord, Tunicata, or water filterers, and Cephalochordata, or those with a notochord for their entire life.
The nervous system of chorata is focused around the presence of a brain, spinal chord and notochord. A notochord is a backbone like structure that forms in all Chordata species. However, in the sub- phyla Vertebrata, the notochord is replace by the spinal chord. Nerves throughout the body transport signlas to and from the spinal chorda and ultimately the brain where it is then decided and sent back.
The nervous system of chorata is focused around the presence of a brain, spinal chord and notochord. A notochord is a backbone like structure that forms in all Chordata species. However, in the sub- phyla Vertebrata, the notochord is replace by the spinal chord. Nerves throughout the body transport signlas to and from the spinal chorda and ultimately the brain where it is then decided and sent back.
Sea squirts- These are filter feeders who live in shallow water and have no vertebrae. These tunicates are sedentary creatures who live attached to rocks or shells. they filter water through special gills in order to trap food.
Lancelet- This sub-phyla of chordate lives its entire life with out loosing its notochord. The anatomy shown below shows how the lancelet has both a spinal chord and notochord and its relation to other chordata species.
1 = bulge in spinal cord ("brain")
2 = notochord
3 = dorsal nerve cord
4 = post-anal tail
5 = anus
6 = digestive canal
7 = circulatory system
8 = atriopore
9 = space above pharynx
10 = pharyngeal slit (gill)
11 = pharynx
12 = vestibule
13 = oral cirri
14 = mouth opening
15 = gonads (ovary / testicle)
16 = light sensor
17 = nerves
18 = metapleural fold
19 = hepatic caecum (liver-like sack