Let me share with you a difference between gastrovascular cavity and alimentary canal.
| Aspect | Gastrovascular Cavity | Alimentary Canal |
| Structure | Single opening (mouth/anus) and a central cavity where digestion and nutrient absorption occur | Two openings (mouth and anus) connected by a tubular passage |
| Function | Functions in both digestion and nutrient distribution (no separate structures for ingestion and egestion) | Specialized structures for ingestion, digestion, absorption and egestion |
| Found In | · Cnidarians (jellyfish and corals) · Flatworms | · Annelids · Arthropods · Mollusks · Vertebrates |
| Nutrient absorption | Nutrients are absorbed directly into the cells lining the gastrovascular cavity | Nutrients are absorbed across the walls of the alimentary canal. |
| Complexity | Relatively simple structure | More complex structure having stomach, small intestine and large intestine. |
| Specialized regions | Typically lacks specialized regions | Often has distinct regions e.g., stomach for storage and initial digestion, small intestine for nutrient absorption etc. |
| Muscular Movement | Contractions of the gastrodermis or body wall move contents within the cavity | Muscular contractions (peristalsis) move contents along the length of the canal |
| Examples
| · Hydra (cnidarian) · Flatworms (planarians) | · Humans · Birds · Insects · Earthworms |