The First Animals to move
Level of Organization
This group has the cell tissue level of organization. The tissues are nerves and muscles.
Cnidarians have just 2 germ layers the endoderm and the ectoderm. They are separated by an unorganized layer the mesoglea.
There is no visible segmentation in this animal group.
Cnidarians possess only one digestive opening, which serves as both the mouth and the anus. This opening is surrounded by tentacles and leads to an internal digestive cavity called the gastrovascular cavity .Cnidarians feed using tentacles that are embedded with stinging nematocysts. Once the prey item has been captured and subdued, tentacles are used by the cnidarians to bring the prey item into the gastrovascular cavity. Within the gastrovascular cavity, the food item is broken into small particles by digestive enzymes secreted by gastrodermal cells lining the cavity. The minute particles are then taken in by the gastrodermal cells, and digestion is completed in digestive vacuoles (small cavities) within these cells. The indigestible remnants of the prey are expelled from the mouth of the gastrovascular cavity.
There is no circulatory system in the cnidarians. All nutritional material and waste is provided to each cell through simple diffusion.