BIO 201 Lecture Notes - Lecture 24: Schistosoma, Polysaccharide, Triploblasty
29 Apr 2016
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Document Summary
In protostomes, the embryonic blastopore becomes the mouth as the animal develops. A ventral nervous system with paired or fused longitudinal nerve cords (#6) Dorsoventrally flattened: no gas transport system, so every cell must be near the surface. Digestive tract: mouth opens into a, often highly branched guy, which increases surface area for absorption of nutrients. Many species are internal parasites- tapeworms and flukes. They absorb digested food from the digestive tract of the host, and have lost digestive organs of their own. The protostome common ancestor has a coelom, but body cavity forms have undergone modifications. Some lineages have lost the coelom and revered to an acoelomate state. As parasitism evolved in the ancestor of protostome, many genes were lost, such as those required for synthesizing fats and cholesterol that are crucial for development. Tapeworms must obtain resources from their host"s diet. Mutations in alleles; neutral with respect to survival/reproduction.
