| Symmetry |
Asymmetrical (lack of) |
Radial symmetry |
Radial symmetry |
Bilateral symmetry |
Bilateral symmetry |
| Germ Layers |
None (lack true tissues) |
Two germ layers (diploblastic) |
Two germ layers (diploblastic) |
Three germ layers (triploblastic) |
Three germ layers (triploblastic) |
| Body Plan |
Simple, lack true tissues/organs |
Simple, central body cavity (gastrovascular cavity) |
Gelatinous, unique ciliary combs |
Flattened, often parasitic, simple digestive system |
Cylindrical body, tough cuticle, diverse lifestyles |
| Nervous System |
Lack a true nervous system |
Simple nerve net and nerve cells |
Simple nervous system |
Primitive nervous system with ganglia |
More developed nervous system with ganglia and nerve cords |
| Special Structures |
Choanocytes for filter-feeding |
Cnidocytes with nematocysts |
Comb rows for locomotion |
Some are parasitic with specialized adaptations |
Tough cuticle, diverse reproductive strategies |
| Habitat and Lifestyles |
Mostly aquatic, sessile filter feeders |
Mostly marine, sessile and free-swimming species |
Marine, planktonic, free-swimming |
Aquatic and terrestrial, free-living and parasitic forms |
Various environments, including soil, aquatic habitats, and parasites |
| Complexity |
Simplest and least complex |
Simple with radial symmetry |
Simple with unique ciliary structures |
More complex, bilateral symmetry |
More complex, bilateral symmetry |
