What derived character distinguishes the anthozoans from all other cnidarians?

Anthozoans are distinguished from other cnidarians by their unique body plan, which includes a polyp form that is typically sessile and lacks a medusa stage. They possess a well-developed gastrovascular cavity divided by partitions called mesenteries, which increase the surface area for digestion and support. Additionally, anthozoans exhibit a unique arrangement of their reproductive structures, often releasing gametes directly into the water column, unlike other cnidarian classes.