Echinoderms
Echinoderms are radially symmetrical, like cnidarians. However, it is only the adult that is radially symmetrical. The planktonic larva are bilaterally symmetrical. Unlike cnidarians, echinoderms have pentamerous radial symmetry, meaning they have symmetry based on 5 parts. Echinoderms lack a head and therefore do not have a posterior or anterior end or dorsal or ventral side. Instead, the side with the mouth is referred to as the oral surface. The opposite side is called the aboral side.
Echinoderms have an internal skeleton, or an endoskeleton. Even though some exhibit a seemingly hard outside, like the spines of the sea urchins, it is covered by a thin layer of ciliated tissue.
The name Echinoderm means "spiny skinned".
Unique to the echinoderms is a water vascular system, which is a network of water-filled canals used for locomotion. Tube feet are muscular extentions of these canals. They are extended when filled with water, sometimes by the action of muscular sacs called ampullae. The tube feet often end in a sucker and are used for attachment, locomotion and the reception of chemical and mechanical stimuli. In sea stars and sea urchins, the system is connected to the outside through the madreporite, which is a porous plate on the aboral surface.
Radial symmetry is associated with a sedentary lifestyle (they have no cephalization to direct movement). With the exception of limited swimming in some feather stars and some deep water sea cucumbers, adult echinoderms are relatively slow bottom crawlers.
Echinoderms have an internal skeleton, or an endoskeleton. Even though some exhibit a seemingly hard outside, like the spines of the sea urchins, it is covered by a thin layer of ciliated tissue.
The name Echinoderm means "spiny skinned".
Unique to the echinoderms is a water vascular system, which is a network of water-filled canals used for locomotion. Tube feet are muscular extentions of these canals. They are extended when filled with water, sometimes by the action of muscular sacs called ampullae. The tube feet often end in a sucker and are used for attachment, locomotion and the reception of chemical and mechanical stimuli. In sea stars and sea urchins, the system is connected to the outside through the madreporite, which is a porous plate on the aboral surface.
Radial symmetry is associated with a sedentary lifestyle (they have no cephalization to direct movement). With the exception of limited swimming in some feather stars and some deep water sea cucumbers, adult echinoderms are relatively slow bottom crawlers.