Most animals and plants are part of more than one food chain. If one part of a food chain alters, the whole food chain is affected. For example, if a disease suddenly wiped out caterpillars, it would affect mice, owls and many other animals.
This phylum consists of the jellyfish, hydra, sea anemones, corals, sea pens, sea wasps, and box jellyfish. There are about 9,000 species. Almost all are marine. This is another ancient group, with fossils perhaps reaching back to 700 mya.
Echinoderms (scientific name Echinodermata) are a major group of only marine animals. The name comes from the Greek word for spiny skin. There are about 7,000 species found usually on the sea floor in every marine habitat from the intertidal zone to the ocean depths.