EEB267H1 Lecture Notes - Lecture 2: Pharyngeal Slit, Ventral Nerve Cord, Chordate

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On a phylogenetic tree of the metazoa (multicellular animals), they are one branch: distant relatives: echinodermata (e. g. ,starfish), hemichordata (e. g. , acorn worms), xenocoelomorpha (marine) In the earthworm, the nerve cord runs along the belly: ventral nerve cord: function: forms the central nervous system spinal nerve cord and brain. Autapomorphy #3: the post-anal tail: function: movement (propulsion) At least 650 million years old based on fossils and molecular data) have not changed much, looks similar today. Approximately 35 species living in burrows in shallow, warm, coastal marine waters. The notochord runs to the anterior tip of the head. Small particles in the water are trapped in mucous surrounding the pharyngeal slits. Cilia in the area roll the mucous full of tasty items into a ball and move it to the gut. Pharyngeal slits are not true gills (yet) not used for breathing but feeding.

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