Sand Dollar
Sand Dollars are flat, burrowing, sea urchins that are small, round and fairly smooth. They have a rigid skeleton made of calcium carbonate plates and this skeleton is covered by small, velvet textured spikes that give them the smooth feel. Their main habitat is in the waters in the Caribbean. They are simple animals, anatomically speaking and they have a simple respiratory system as well.
Sand dollars respirate by a process called diffusion that occurs in their tube feet, much like those of a star-fish. Diffusion is the passive movement of molecules or particles along a concentration gradient, or from regions of higher to regions of lower concentration. This means that oxygen travels across their tube feet membrane and carbon dioxide emissions are sent out through the same process.
Sand dollars respirate by a process called diffusion that occurs in their tube feet, much like those of a star-fish. Diffusion is the passive movement of molecules or particles along a concentration gradient, or from regions of higher to regions of lower concentration. This means that oxygen travels across their tube feet membrane and carbon dioxide emissions are sent out through the same process.