The amphioxus (Branchiostoma lanceolatum in the photo on the left) is an organism whose organization allows to have a first approach of the general organization of the Chordés branch. It belongs (like us) to the sub-branch of Myomerozoans because it has somites during its development that will evolve into myomers. It is more precisely a Cephalochordata because the chorus extends over the entire length of the body, from the tail to the rostrum in front of the mouth. Different sequences are shown. An overview of the body allows you to locate the main tissues and organs. A sequence clearly shows the path of water and food from the mouth to the atriopore and anus respectively. These displacements are further illustrated on a large diagram of a few myomers and which also highlights the arrangement of different tissues in the gill basket. In the last sequence, these same tissues are illustrated in more detail by reconstructing the segments from the arcs of the gill basket. Particular attention is paid to the organization of the excretory system and the gill basket with primary and secondary arches.
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