Answer:
cephalochordates
Explanation:
Cephalochordata is one of the subphylos of the phylum Chordata with about 30 species. Cephalocords are small (centimeter long) animals, thin, laterally flattened (like the body of fish), transparent and live buried in sandy substrates leaving only their heads apparent. They are currently represented by the amphioxes. Cephalocords are the group of invertebrates that is most related to vertebrates.
The body of the cephalocordates is composed of longitudinal (horizontal) muscles that are divided by blocks called myotomes. The notochord holds in adults giving a stronger structure to the body.
