EEB267H1 Lecture Notes - Lecture 2: Tunicate, Mechanoreceptor, Autapomorphy
11 Jan 2017
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Metazoans: any multicellular animal that has an embryo which starts with three germ layers. Deuterostomes: anus develops first (before the mouth) in embryo development. Some extant and extinct species of the above sister groups have this trait: pharyngeal slits are older than chordata and appear in other taxon. Each is supported by a pair of cartilaginous rods: compare to slits in a piece of paper they will not stay open on their own, all chordates have this. Their function is feeding and/or respiration depending on the species. Not gills, but often called gill bars. Or chordata autapomorphies: a distinct feature unique to a taxon. Dorsal, hollow nerve cord notochord function is to form the central nervous system, or the spinal nerve cord + brain invertebrates have a solid, ventral nerve: why or how such a complete change occurred is not clear. Consists of a hollow rod made of cartilage (collagen, elastin) filled with vacuoles.
