How are cnidarians different from other invertebrates?

Cnidarians are distinguished from other invertebrates by several unique biological characteristics and a relatively simple body organization.12

Key differences include:

• Stinging Capsules: Only cnidarians produce microscopic intracellular stinging capsules known as nematocysts or cnidae, which are used for defense and capturing prey.13
• Body Symmetry and Layers: They exhibit radial symmetry and possess only two cell layers, whereas more complex animals have three.2
• Organization: They are the most primitive animals with cells organized into distinct tissues, yet they lack true organs.2
• Body Plan: Their bodies are organized around a single central cavity called the coelenteron, which has only one opening that serves as both the mouth and the exit for waste.12
• Nervous System: They lack a centralized brain or ganglia, relying instead on a primitive nerve net to coordinate movement and sensory input.45
• Body Forms: Many species alternate between two distinct body forms: the sedentary polyp and the free-swimming medusa.2