I believe runoff would be the answer.
The phylum Echinodermata , which contains about 6000 species, gets its name from the Greek, literally meaning "spiny skin." Many echinoderms actually do have "spiny" skin, but others do not. This phylum exists exclusively in the sea, and cannot be found on land or in fresh water.
Answer:
because they have thicker walls
Explanation:
blood is punped our of the heart very fast which means it would need a blood vessel witch thick walls to withstand the pressure. thin walls would cause the blood vessle damage and may evwn break as it wouldn't be able to withstans the pressure.
