All of the remaining groups share characteristics such as a true coelom and development in which the blastopore forms the anus. I. Phylum Echinodermata Echinoderm translates as spiny skin all echinoderms have a thin skin that covers a hard exoskeleton, and most have bumps and spines that serve various functions including protection and camouflage.
Most echinoderms are sessile or sedentary marine forms with radial symmetry as adults.
A unique feature is the water vascular system, which is a network of hydraulic canals, which branch into tube feet that function for locomotion, feeding, and gas exchange. This is a group lacking some essential characteristics of chordates. A representative hemichordate is the acorn worm Balanoglossus. Balanoglossus has some characteristics in common with chordates, such as gill slits and a dorsal nerve cord. However, this species also has a ventral nerve cord, and the nerve cords in general are not hollow like most chordates, but instead are solid.