Describe for hydra, nematodes and planarians:
- germ layers
- body covering
- coelomic cavity
- digestive tract and digestion
- nervous system
- sense organs
- sexual reproduction
- asexual reproduction
Animals with bilaterial symmetry are better at directional movement. Animals with radial symmetry are normally just animals that interact with their environment from all angles because they cannot move with purpose very well. Cephaliazation is associated with bilaterial symmetry and concentrates the nervous development to one end of the animal, many times the head. The advantage is that having all of your sensory organs on one end improves movement and reactions to your environment. Especially when associated with directional movement. Radial organisms such as hydra remove waste by releasing it into its environment. Planaraians have eye spots that have no lens and don't move. These planarians move using cilia with mucus as well as muscles that send contractions throughout the body of the animal. Planarians use there auricles for smelling and sensing the environment around them. If you place a strong beam of light on the planarians you would see the animals move away from light sources, depending on the angle from which the light is originating.
Planarians have a digestion mechanism that branches diverticula that extend laterally from the intestinal trucks. This is an advantage because you can distribute the nutrients to all cell of the animal.
Epithelial cells of the planarian are only ciliated on the ventral side of the animal and serve to ...
Hydra, nematodes and planarians are described.