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.
Crustaceans include commonly-known marine life such as crabs, lobsters, barnacles and shrimp. These animals are in the Phylum Arthropoda (the same phylum as insects) and Subphylum Crustacea. According to the Natural History Museum of Los Angeles County, there are over 52,000 species of crustaceans.