Gaseous exchange..............
Predators and prey are both in a constant struggle for survival, foxes with bigger ears tend to catch more mice, and live longer, because of this, foxes with smaller ears don't live as long, pretty soon all foxes have larger ears. The same goes for prey, Mice with padded feet live longer due to the foxes having more trouble hearing them, pretty soon all mice have padded feet, and the cycle continues.
Despite their seemingly simple anatomy and radial symmetry Sea urchins and sea star are a type of deuterostome, closely related to the chordates.
What are the characteristics of deuterostome?
Animals classified as deuterostomes share a common embryonic development.
The first opening during development known as the blastopore changes to the anus in deuterostomes while the mouth changes in protostomes.
They have a coelom, which forms as a result of enterocele (coelom from the digestive tract).
These creatures include the following,
- Chordata,
- Echinodermata,
- Hemichordata.
Hence the correct answer is Deuterostome.
Learn more about Deuterostome,
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'The Fetus' would be the correct answer.