What new structural adaptations appear in the fossils of the cambrian explosion that were not present in the precambrium period?

Several structural adaptations has taken place during the Cambrian explosion such as-

The transformation of simple unicellular organisms such as bacteria, blue green algae, appearing in the precambrian age, to a much more complex multicellular organisms. For example, jellyfish.Evolution took place producing cartilageous bond in the organism. For example, fishes.Body growth and anatomical changes within the organism occured and reproductive system has developed.

The answer will be d