Marine life, or sea life or ocean life, is the plants, animals and other organisms that live in the salt water of the sea or ocean, or the brackish water of coastal estuaries. At a fundamental level, marine life affects the nature of the planet. Marine organisms produce oxygen. Shorelines are in part shaped and protected by marine life, and some marine organisms even help create new land. The term marine comes from the Latin mare, meaning sea or ocean.
Most life forms evolved initially in marine habitats. By volume, oceans provide about 90 percent of the living space on the planet. The earliest vertebrates 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 forms the general foundation of the ocean food chain, particularly the phytoplankton which are key primary producers.
Marine invertebrates exhibit a wide range of modifications to survive in poorly oxygenated waters, including breathing tubes as in mollusc siphons. 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.
A total of 230,000 documented marine species exist, including about 20,000 species of marine fish, with some two million marine species yet to be documented. Marine species range in size from the microscopic, including plankton and phytoplankton which can be as small as 0.02 micrometres, to huge cetaceans (whales, dolphins and porpoises), including the blue whale – the largest known animal reaching 33 metres (108 ft) in length. Marine microorganisms, including bacteria and viruses, constitute about 70% of the total marine biomass.
Giant squid, once believed to be mythical creatures, are squid of the Architeuthidae family, represented by as many as eight species of the genus Architeuthis. They are deep-ocean dwelling animals that can grow to a tremendous size: recent estimates put the maximum size at 10 meters (34 ft) for males and 13 meters (44 ft) for females from caudal fin to the tip of the two long tentacles (second only to the Colossal Squid at an estimated 14 meters (46 ft), one of the largest living organisms).
The mantle length, though, is only about 2 meters (7 ft) in length (more for females, less for males), and the length of the squid excluding its tentacles is about 5 meters (16 ft). There were reported claims of specimens of up to 20 meters (66 ft), but none had been scientifically documented.
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Felix Anton Dohrn ( September 29, 1840 - September 26, 1909) was a prominent Darwinist and the founder and first director of the Stazione Zoologica, Naples, Italy.
Dohrn was born in Stettin, Pomerania, present day Poland, in 1840, into a wealthy middle class family. His grandfather, Heinrich Dohrn, had been a wine and spice merchant, and had made the family fortune by trading in sugar. This wealth allowed Anton's father, Carl August, to devote himself to his various hobbies; travelling, folk music and insects. Anton, the youngest son, read zoology and medicine at various German universities (Königsberg, Bonn, Jena and Berlin), with little application or enthusiasm for his studies.
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Did you know...
- Triggerfishes are the brightly coloured fishes of the family Balistidae. (pictured)
- The sea otter often keeps a stone tool in its armpit pouch.
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Photo credit: Tokugawapants
The Green Sea Turtle (Chelonia mydas) is a large sea turtle, the only member of the genus Chelonia (Brongniart, 1800). This turtle grows to 1-1.5 m in length, and can weigh 200 kg, making it the largest of the hard-shelled turtles. Its distribution extends throughout tropical, subtropical and some warmer temperate waters. Females lay their eggs on traditional nesting beaches, and the turtles often bask in the sand to warm their ectothermic bodies, but otherwise this species is entirely marine.
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