Marine life appeared in the form of fish, which live exclusively in water. Some of these evolved into amphibians which spend portions of their lives in water and portions on land. Other fish evolved into land mammals and subsequently returned to the ocean as seals, dolphins or whales. Plant forms such as kelp and algae grow in the water and are the basis for some underwater ecosystems. Plankton, and particularly phytoplankton, are key primary producers forming the general foundation of the ocean food chain. Marine invertebrates exhibit a wide range of modifications to survive in poorly oxygenated waters including breathing tubes (see
Shrimp and prawn as food Shrimp and prawn as food Shrimp and prawn are important types of seafood that are consumed worldwide. Although shrimp and prawns belong to different suborders of Decapoda, they are very similar in appearance and the terms are often used interchangeably in commercial farming and wild fisheries. A distinction is drawn in recent aquaculture literature, which increasingly uses the term "prawn" only for the freshwater forms of palaemonids and "shrimp" for the marine penaeids. In the United Kingdom, the word "prawn" is more common on menus than "shrimp"; the opposite is the case in North America. The term "prawn" is also