Aquatic life forms

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Aquatic life forms

Post  meodingu on Wed Oct 13, 2010 11:24 pm

Aquatic life forms
Main articles: Hydrobiology and Aquatic plant
Some marine diatoms – a key phytoplankton group

Earth's surface waters are filled with life. The earliest life forms appeared in water; nearly all fish live exclusively in water, and there are many types of marine mammals, such as dolphins and whales. Some kinds of animals, such as amphibians, spend portions of their lives in water and portions on land. Plants such as kelp and algae grow in the water and are the basis for some underwater ecosystems. Plankton is generally the foundation of the ocean food chain.

Aquatic vertebrates must obtain oxygen to survive, and they do so in various ways. Fish have gills instead of lungs, although some species of fish, such as the lungfish, have both. Marine mammals, such as dolphins, whales, otters, and seals need to surface periodically to breathe air. Some amphibians are able to absorb oxygen through their skin. Invertebrates exhibit a wide range of modifications to survive in poorly oxygenated waters including breathing tubes (Diptera and some molluscs) and gills (Carcinus). However as invertebrate life evolved in an aquatic habitat most have little or new specialisation for respiration in water.





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