According to the Embryological studies, the most ancient chordates were closely related to the ancestors of the echinoderms. Echinoderms are members of the group Phylum Echinodermata of marine animals. Some known echinoderms are starfish, and sea cucumbers.
The unified cell theory states that: all living things are composed of one or more cells; the cell is the basic unit of life; and new cells arise from existing cells. Rudolf Virchow later made important contributions to this theory.
