Marine Organizations
When you look out over the ocean, it appears to be nothing more than a big basin filled with water, so it's hard to imagine that under the surface of the water there is a rich, biologically-diverse community of organisms. These ocean-dwelling organisms, known as marine organisms, live in a variety of underwater habitats, and the habitats vary based on the chemical and physical properties of that section of the ocean. In fact, properties such as the salt content of the water, temperature, light penetration, and ocean currents dictate where different marine organisms live within the vast oceans of planet Earth. In this lesson, you will learn about the varied and somewhat bizarre organisms that inhabit the world under the sea.
Dolphin is the common name for aquatic mammals within the infraorder Cetacea. The term dolphin usually refers to the extant families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the brackish dolphins), and the extinct Lipotidae (baiji or Chinese river dolphin ). There are 40 extant species named dolphins.
seal, any of 32 species of web-footed aquatic mammals that live chiefly in cold seas and whose body shape, round at the middle and tapered at the ends, is adapted to swift and graceful swimming. There are two types of seals: the earless, or true, seals (family Phocidae); and the eared seals (family Otariidae), which include the sea lions and fur seals. In addition to the presence of external ears, earless seals have longer flippers than earless seals. Also, the fur of eared seals is more apparent, especially in sea lions.
Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven-gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha (or Selachii) and are the sister group to the rays. However, the term "shark" has also been (incorrectly) used to refer to extinct members of the subclass Elasmobranchii, which are technically outside the Selachimorpha clade. Notable examples of improper classification include Cladoselache, Xenacanthus, and various other members of the Chondrichthyes class like the holocephalid eugenodontidans.
Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or baskets stars. Starfish are also known as asteroids due to being in the class Asteroidea. About 1,900 species of starfish occur on the seabed in all the world's oceans, from warm, tropical zones to frigid, polar regions. They are found from the intertidal zone down to abyssal depths, at 6,000 m (20,000 ft) below the surface.
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