Echinozoa
Echinozoa is a subphylum of the phylum Echinodermata. Echinoderms are marine invertebrates characterized by radial symmetry, a water vascular system, and a calcareous skeleton. The subphylum Echinozoa includes living groups such as sea urchins, sand dollars, and brittle stars, as well as fossil forms. A key characteristic of echinozoans is the absence of arms, which are present in other echinoderm subphyla like Asterozoa (starfish and brittle stars). Instead, echinozoans typically have a globular or flattened, disc-like body.
The body of an echinozoan is generally divided into five distinct sections, reflecting their pentaradial symmetry.
Living echinozoans are primarily benthic, meaning they live on the seafloor, where they can be found in