Ancient chordates are thought to be most closely related to echinoderms because the embryos of chordates and echinoderms are

Both show similarities in their embryos- Radial cleavage, Indeterminate cleavage and blastopore become the tail end.

Explanation:

Chordates and echinoderms show similarities in their embryological development-

1. Radial cleavage: in there 8 cell stage has 2 different tiers of cells, 4 cells each. Each cell directly above or below another.

2. Indeterminate cleavage: cells can develop into an entire embryo if separated in an early stage.

3. Blastopore turns into the tail end or posterior end except for few molluscs and other protosomes.

i am going to guess that it is co2.

4.) metal

"-the movement of carbon from the nonliving environment into living things and back to the environment

-carbon is the essential component of proteins, fats, and carbohydrates (which make up all organisms)

-carbon exists in air, water, and living organisms

-producers convert carbon dioxide in the atmosphere into carbohydrates during photosynthesis

-bacteria in the atmosphere cycles through the system in filtration units

-in cellular respiration, carbon is released back into the atmosphere as carbon dioxide

-some carbon is stored in limestone (forming one of the largest "carbon sinks" on earth)

-largest carbon reservoir on earth= limestone

-carbon stored in the bodies of organisms as fat, oils, or other molecules may be released into the soil or air when the organism dies

-this may form deposits of coal, oil, or natural gas (fossil fuels, which increased the atmospheric carbon dioxide)

-fossil fuels store carbon left over from bodies of organisms that died millions of years ago

-they are located in the surface of earth, deep within the earth and beneath the ocean floor."