Echinoderms, like chordates, are deuterostomes and are therefore thought to be the most closely related of the major phyla to the chordates
Some molecular studies point to amphibians descending from the lung fish, the Diponi.
Under the class Amphibia, amphibians are tetra-pod, cold blooded vertebrates without having scales. Protein is produced by the special skin of Amphibians.
Lung fish belong to the subclass of Diponi, these are living air breathing species.
Answer:
Why are cells small? because they can absorb nutrients much more efficiently. Because they are smaller they can efficiently absorb enough food. When a cell doubles in size the volume increases much more then the surface area, which is why large cells cannot receive enough food efficiently for their volume.
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