The oceanic zone is typically defined as the area of the ocean lying beyond the continental shelf (e.g. the neritic zone ), but operationally is often referred to as beginning where the water depths drop to below 200 metres (660 ft), seaward from the coast into the open ocean with its pelagic zone .
27-543: Telephinidae is a family of pelagic trilobites with large wide-angle eyes, occupying most of the free cheeks, downward directed facial spines and 9-10 thorax segments. The family is known during the entire Ordovician and occurred in deep water around the globe. The Telephinidae probably evolved from a species assigned to the Hystricuridae. Telephinids first occur during the late Tremadocian , with Carolinites and Opipeuterella being globally very common at low latitudes by
54-420: A circular cross section, or modified to form a pair of short spines. The free cheeks curve strongly downwards and have prominent borders, particularly to the side and the back, and these bear long tube- or blade-like genal spines. The articulating middle part of the body (or thorax ) consists of 9 or 10 segments. The axis is extremely convex and the side-lobes (or pleurae) are narrow. The tailshield (or pygidium )
81-469: A typical adaptation to a lightless environment, and oceanic free-floating graptolites. Telephinidae however also occur with sighted benthic trilobites and other organisms. Comparison of the angles and densities of the facets shows that the eyes of the Telephinidae were less adapted to low-light levels and therefore cyclopygids are considered to have been confined to deeper water, swimming at the lower limit of
108-494: Is convex and its axis is prominent and has 2-4 rings. The most backward piece may bear a long spine. The seam of the exoskeleton (or doublure ) is narrow. Cyclopigids lack genal spines and palpebral lobes. Their thorax has 5 to 7 segments. The occipital ring is present only in the Ellipsotaphrinae subfamily. Like the contemporary but unrelated Cyclopygidae , Telephinidae occur with blind or nearly blind benthic trilobites,
135-556: Is higher here, it can be up to 10,100 kilopascals (1,460 psi) and increases with depth. 54% of the ocean lies in the Bathypelagic (aphotic) zone into which no light penetrates. This is also called the midnight zone and the deep ocean. Due to the complete lack of sunlight, photosynthesis cannot occur and the only light source is bioluminescence. Water pressure is very intense and the temperatures are near freezing (range 0 to 6 °C (32 to 43 °F)). Oceanographers have divided
162-404: Is subdivided into five vertical regions. From the top down, these are: The illuminated zone at the surface of the sea with sufficient light for photosynthesis. Nearly all primary production in the ocean occurs here, and marine life is concentrated in this zone, including plankton , floating seaweed , jellyfish , tuna , many sharks and dolphins . The most abundant organisms thriving into
189-490: Is the ecological region at the very bottom, including the sediment surface and some subsurface layers. Marine organisms such as clams and crabs living in this zone are called benthos . Just above the benthic zone is the demersal zone. Demersal fish can be divided into benthic fish , which are denser than water and rest on the bottom, and benthopelagic fish , which swim just above the bottom. Demersal fish are also known as bottom feeders and groundfish . The pelagic zone
216-481: The Greek underworld . This is the deepest part of the ocean at more than 6,000 m (20,000 ft) or 6,500 m (21,300 ft), depending on authority. Such depths are generally located in trenches . The pelagic ecosystem is based on phytoplankton . Phytoplankton manufacture their own food using a process of photosynthesis . Because they need sunlight, they inhabit the upper, sunlit epipelagic zone, which includes
243-497: The albatross , Procellariidae and petrels . Oceanic zone It is the region of open sea beyond the edge of the continental shelf and includes 65% of the ocean's completely open water. The oceanic zone has a wide array of undersea terrain, including trenches that are often deeper than Mount Everest is tall, as well as deep-sea volcanoes and basins . While it is often difficult for life to sustain itself in this type of environment, many species have adapted and do thrive in
270-411: The hadopelagic . Coastal waters are generally the relatively shallow epipelagic. Altogether, the pelagic zone occupies 1,330 million km (320 million mi ) with a mean depth of 3.68 km (2.29 mi) and maximum depth of 11 km (6.8 mi). Pelagic life decreases as depth increases. The pelagic zone contrasts with the benthic and demersal zones at the bottom of the sea. The benthic zone
297-500: The water column of coastal, ocean, and lake waters, but not on or near the bottom of the sea or the lake. They can be contrasted with demersal fish, which do live on or near the bottom, and coral reef fish . Pelagic fish are often migratory forage fish , which feed on plankton , and the larger predatory fish that follow and feed on the forage fish. Examples of migratory forage fish are herring , anchovies , capelin , and menhaden . Examples of larger pelagic fish which prey on
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#1732844372203324-753: The coastal or neritic zone . Biodiversity diminishes markedly in the deeper zones below the epipelagic zone as dissolved oxygen diminishes, water pressure increases, temperatures become colder, food sources become scarce, and light diminishes and finally disappears. Some examples of pelagic invertebrates include krill , copepods , jellyfish , decapod larvae , hyperiid amphipods , rotifers and cladocerans . Thorson's rule states that benthic marine invertebrates at low latitudes tend to produce large numbers of eggs developing to widely dispersing pelagic larvae, whereas at high latitudes such organisms tend to produce fewer and larger lecithotrophic (yolk-feeding) eggs and larger offspring. Pelagic fish live in
351-605: The end of the Floian . Carolinites survived into the Darriwilian , at which time a second major radiation occurred, that includes Telephina and Telephops , and these genera only became extinct at the end of the Ordovician. The central raised area of the headshield (or glabella ) is strongly convex. The most backward segment (called occipital ring) is wide and is defined by a deep furrow. No further segments can be determined in front of
378-512: The first years of their lives in the pelagic zone, moving closer to shore as they reach maturity. Pelagic birds , also called oceanic birds or seabirds , live on open seas and oceans rather than inland or around more restricted waters such as rivers and lakes. Pelagic birds feed on planktonic crustaceans , squid and forage fish . Examples are the Atlantic puffin , macaroni penguins , sooty terns , shearwaters , and Procellariiformes such as
405-477: The forage fish are billfish , tuna , and oceanic sharks . Hydrophis platurus , the yellow-bellied sea snake, is the only one of the 65 species of marine snakes to spend its entire life in the pelagic zone. It bears live young at sea and is helpless on land. The species sometimes forms aggregations of thousands along slicks in surface waters. The yellow-bellied sea snake is the world's most widely distributed snake species. Many species of sea turtles spend
432-553: The mesopelagic zone are heterotrophic bacteria. Animals living in this zone include swordfish , squid , wolffish and some species of cuttlefish . Many organisms living here are bioluminescent . Some mesopelagic creatures rise to the epipelagic zone at night to feed. The name stems from Ancient Greek βαθύς 'deep'. The ocean is pitch black at this depth apart from occasional bioluminescent organisms, such as anglerfish . No plants live here. Most animals survive on detritus known as " marine snow " falling from
459-431: The number of layers depending on the depth of the water. Marine life is affected by bathymetry (underwater topography) such as the seafloor, shoreline, or a submarine seamount , as well as by proximity to the boundary between the ocean and the atmosphere at the ocean surface, which brings light for photosynthesis, predation from above, and wind stirring up waves and setting currents in motion. The pelagic zone refers to
486-402: The occipital ring, but sometimes 2-4 pairs of muscle impressions are visible, of which the one just in front of the occipital ring may be deepened at its inner end (in some Telephina species) to form a lengthwise furrow. The fixed cheeks have broad palpebral lobes (between the eye and the glabella) that take up most of the length of headshield. The frontal border of the headshield is arched, with
513-410: The ocean floor that expel superheated water that is rich in minerals. These organisms feed off of chemosynthetic bacteria, which use the superheated water and chemicals from the hydrothermal vents to create energy in place of photosynthesis. The existence of these bacteria allow creatures like squids, hatchet fish, octopuses, tube worms, giant clams, spider crabs and other organisms to survive. Due to
540-530: The ocean into zones based on how far light reaches. All of the light zones can be found in the oceanic zone. The epipelagic zone is the one closest to the surface and is the best lit. It extends to 100 meters and contains both phytoplankton and zooplankton that can support larger organisms like marine mammals and some types of fish. Past 100 meters, not enough light penetrates the water to support life, and no plant life exists. There are creatures, however, which thrive around hydrothermal vents, or geysers located on
567-565: The oceanic zone. The open ocean is vertically divided into four zones: the sunlight zone , twilight zone , midnight zone , and abyssal zone . The Mesopelagic (disphotic) zone, which is where only small amounts of light penetrate, lies below the Epipelagic zone . This zone is often referred to as the "Twilight Zone" due to its scarce amount of light. Temperatures in the Mesopelagic zone range from 5 to 4 °C (41 to 39 °F). The pressure
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#1732844372203594-408: The open, free waters away from the shore, where marine life can swim freely in any direction unhindered by topographical constraints. The oceanic zone is the deep open ocean beyond the continental shelf , which contrasts with the inshore waters near the coast , such as in estuaries or on the continental shelf. Waters in the oceanic zone plunge to the depths of the abyssopelagic and further to
621-518: The photic zone (or mesopelagic). This implies Telephinidae lived higher up in the water column, possibly hunting plankton . Because of the weight, Telephinidae probably swam back-down. Pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word pelagic is derived from Ancient Greek πέλαγος ( pélagos ) 'open sea'. The pelagic zone can be thought of as an imaginary cylinder or water column between
648-451: The surface of the sea and the bottom. Conditions in the water column change with depth: pressure increases; temperature and light decrease; salinity, oxygen, micronutrients (such as iron, magnesium and calcium) all change. In a manner analogous to stratification in the Earth's atmosphere , the water column can be divided vertically into up to five different layers (illustrated in the diagram), with
675-413: The total darkness in the zones past the epipelagic zone, many organisms that survive in the deep oceans do not have eyes, and other organisms make their own light with bioluminescence. Often the light is blue-green in color, because many marine organisms are sensitive to blue light. Two chemicals, luciferin, and luciferase that react with one another to create a soft glow. The process by which bioluminescence
702-406: The zones above or, like the marine hatchetfish , by preying on other inhabitants of this zone. Other examples of this zone's inhabitants are giant squid , smaller squid and the grimpoteuthis or "dumbo octopus". The giant squid is hunted here by deep-diving sperm whales . The name is derived from Ancient Greek ἄβυσσος 'bottomless' - a holdover from times when the deep ocean
729-410: Was believed to indeed be bottomless. Among the very few creatures living in the cold temperatures, high pressures and complete darkness here are several species of squid; echinoderms including the basket star , swimming cucumber, and the sea pig ; and marine arthropods including the sea spider . Many species at these depths are transparent and eyeless. The name is derived from the realm of Hades ,
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