Detecci´on sitios de uni´on del anti-PD-1

marine explorer who, together with Emile Gagnon, developed SCUBA (self-contained underwater breathing appara-tus) diving in 1943. After World War II, Cousteau and others created the Under-sea ReUnder-search Group at Toulon, France, which became a center for research in undersea study and techniques.

Through his books and fi lms, Cous-teau has promoted interest in life in the sea and the great need for careful use of the marine environment. In 1968 he was asked to make a television series. For the next eight years, The Undersea World of Jacques Cousteau introduced the public to a world of sharks, whales, dolphins, sunken treasure, and coral reefs. In 1974 Cousteau started the Cousteau Soci-ety to protect ocean life. The member-ship of this non-profi t group has grown to include more than 300,000 members worldwide. Cousteau was awarded the Medal of Freedom by President Ronald Reagan in 1985, and in 1989 he was hon-ored by France with membership in the French Academy. His works have repeat-edly stressed the need for intelligent use of the seas, control of pollution and over-fi shing, the use of mariculture, and the preservation of coastal areas. He was the director of the oceanographic institution founded by Albert I of Monaco. Cous-teau died on June 25, 1997. See diving, mariculture, scuba.

cowrie

A marine snail of the family Cypraeidae. There are about 300 species of these beautiful animals. They are usu-ally found in warm seas; the greatest num-ber of species are from the eastern Pacifi c.

Cowries have been traded extensively for many years; their fairly heavy, glossy shells have been used as decoration and coinage, including African decorations that have used Asiatic cowries. See Gastropoda.

crab

A crustacean with a broad, fl at body, a tiny abdomen usually tucked under the cephalothorax, and fi ve pairs of

walk-ing legs. The crabs range in size from 1.5 mm (0.1 inch) to 3.5 m (12 feet) in diam-eter. True crabs, of which there are about 4,500 species, are distributed worldwide and have a range from mudfl ats to abyssal depths of 3,500 m or 12,000 feet. Some freshwater and terrestrial forms also exist, although most species are marine. They feed on a range of organisms from plank-ton to live prey or detritus.

True crabs have up to 19 pairs of appendages, such as antennae, antennules, mouthparts, gill ventilators (mandibles and maxillipeds), walking legs (pereopods and chelipeds), and swimmerets (pleo-pods), which are copulatory organs on the male and egg-carrying devices on the female. In the true crab only, the skeletal plate above the mouth is fused to the chi-tinous shell, or carapace.

The classifi cation of crabs is subject to differing opinions. One scheme is as fol-lows:

Macrura—crayfi sh and lobsters Anomura—hermit crabs Brachyura—true crabs

The true crabs are then subdivided into the following groups:

1. Gymnopleura, primitive crabs of which there are about 30 species. They have long bodies and undeveloped chelipeds.

2. Dromiacea, also primitive but number-ing about 250 species. On these crabs the fi fth pair of walking legs is on the back. These legs hold a piece of cam-oufl age, such as a leaf, clump of algae, or sponge.

3. Oxystomata, burrowing crabs con-stituting about 500 species. Some of these crabs also hold onto pieces of camoufl age.

4. Brachygnatha, comprising about 80%

of all crabs, and numbering about 3,600 species. These crabs have a

Cousteau, Jacques-Yves

square mouthframe and have lost the fi rst pair of swimmerets. This group is further divided into the (a) Oxyrhyn-cha, or Spider crabs, and other quick-moving crabs with hard shells, which have a triangular body shape, narrow head, and a body covered with spines and some camoufl age, and the (b) Brachyrhyncha, the best known group of crabs, which range from pea crabs that live in the mantles of oysters and clams, feeding on whatever the oyster dropped, to the commercially impor-tant edible crabs, stone crab, blue crab, and Dungeness crab. The tropical, ter-restrial Gecarcinidae return to the sea only to breed; the Jamaican tree crab and the Japanese spider crab are part of this large group.

See Arthropoda, cephalothorax, chela, Decapoda, individual names.

crabeater seal

Lobodon carinophagus, is a misnamed Antarctic animal. This seal feeds on krill, not crabs, and has teeth that act collectively to fi lter these tiny animals from the seawater. See krill, seal.

Cretaceous period

A period in the his-tory of life on Earth, the Cretaceous began about 136 million years ago and lasted for about 70 million years. It is the most recent period of the Mesozoic era.

Geologically and geographically, the Cretaceous was a very eventful segment in the Earth’s history. The southern conti-nent, Gondwanaland, was still essentially intact, but the Indian subcontinent had detached and started drifting northward.

By the mid-Cretaceous, South America had moved away from Africa. North America began to move west, away from Europe, opening the Atlantic, while Africa moved north toward Europe, closing the Tethys Sea and beginning the folding that resulted in the Alps.

The folding of the North American continent that eventually produced the Rocky Mountains also began in the Cre-taceous. By the end of the Cretaceous,

New Zealand had separated from Austra-lia and AustraAustra-lia itself was moving away from Antarctica.

The climate during most of the Creta-ceous was warm. Shallow seas extended over large areas of all continents. The dominant sea animals were the ammo-nites. Belemnites, brachiopods, echi-noderms, and mollusks were widely dispersed. Seagoing reptiles such as the ichthyosaur and the plesiosaur were alive.

On land, the dinosaurs reached their zenith during this period, and by its end were extinct. The end of the Cretaceous was marked by the extinction of large numbers of species. See extinction, Appendix: Geologic Timescale.

Crinoidea

Class of fi lter-feeding echino-derms especially abundant in the western Pacifi c Ocean that was once thought to be extinct; the fi rst description of this class of these animals was by Agricola (1546), and they were later depicted in Gesner’s encyclopedia (1565). A living feather star was described in 1592 by Fabio Columna, who thought it was a variety of sea star (starfi sh). It was not until 1761 that a liv-ing stalked crinoid was found. This group of very ancient sea creatures includes the stalked, sessile (stationary) sea lily and the mobile feather stars. In fact, the unstalked feather stars account for most of the 690 living crinoid species. The Mesozoic era was the high point in crinoid development.

The greatest number of species—more than 5,000 have been identifi ed—and indi-viduals lived then.

Crinoids are covered by unique exterior calcareous plates held together by collagen ligaments. Broken body parts regenerate.

The rate of regeneration has recently been studied using the evidence of such rebuild-ing of body parts in the Paleozoic. Studies of crinoids from the Ordovician to Penn-sylvanian periods—approximately 490 mil-lion to 290 milmil-lion years ago—have shown that regeneration rates increased markedly after the appearance of predatory shell-crushing fi sh. This occurred in the mid-Paleozoic Era, around 380 million years

Crinoidea

ago, and is referred to as the Paleozoic marine revolution. Ordinarily, the crinoids are avoided by predators; it is thought that the animals that live on the crinoids were the intended targets, and the crinoids were broken in these encounters. The ultimate

result was that the crinoids that could best regenerate were the ones that survived.

This is an example of predator-prey–driven evolution. See Echinodermata, preda-tor-prey relationships.

crinozoa

A subphylum of Echinoder-mata.

Cromwell Current

An equatorial, subsurface fl ow that appears in three major oceans. The Cromwell Current is the equatorial eastward-fl owing under-current embedded in the westward mov-ing surface current. It is about 300 m (900 feet) wide and about 20 m (70 feet) deep, and moves along at a rate of 2 to 3 knots. See currents.

Crossopterygii

An ancient subclass of the bony fi shes. These animals are related to lungfi sh and are sometimes called lobe-fi sh. The coelacanth is the only survivor.

The Crossopterygii are important because they were the probable progenitors of amphibia. The dorsal fi ns have fl eshy pedi-cels from which the fi n rays emerge. These may have been the precursors of limbs.

See coelacanth.

crown of thorns

A large sea star, (Acanthaster planci) averaging 40 to 45 cm (16 to 18 inches) in diameter, with 12 to 20 arms and covered with red, thick, strong spines. This echinoderm feeds on living coral. A large increase in the crown of thorns population in the 1960s in Aus-tralia resulted in the destruction of large areas of coral on the Great Barrier Reef.

One possible reason for the population boom may have been the removal of many triton snails by shell collectors. More nor-mal reef conditions have brought the pred-ator population into better control. The crown of thorns overpopulation had also affected other areas in the Pacifi c where the coral is now recovering. See coral, Echinodermata, sea stars.

crust

The topmost layer of the Earth.

The ocean fl oor is basaltic; the continental

crinozoa

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Crinoid (sea lily)

crust, which is much thicker than that of the ocean, is largely granitic. See discon-tinuity layer, moho, ocean floor.

Crustacea

A worldwide class of arthro-pods that includes crabs, shrimps, lobsters, and barnacles. There are eight subclasses of the Crustacea and over 25,000 species.

They are present in every type of marine biome and are the aquatic analogs of insects. Both fi ll their respective ecological niches with incredible numbers of species and numbers of individuals. Most crus-taceans are aquatic and breathe through brachioles leading from gills. They have fi ve pairs of cephalic appendages: anten-nae or antennules (or both), mandibles, and maxillae or maxillules or both. The body is divided into a head, thorax, and abdomen and is covered by a chitin-ous exoskeleton. The last body segment (somite) is the telson or tail, which lacks any appendages. The crustaceans have the typical arthropod circulatory system, with an open heart.

The excretory system consists of a primitive network leading to a pair of glands under the antennules. There is one simple median eye and two compound lateral eyes. Generally, the antennae are more effective in testing the environment than are the eyes. Most crustaceans are dieceous (having distinct male and female forms). Fertilization of the eggs is inter-nal. The female is the usual brooder, car-rying the eggs about on her abdominal appendages, which affords some protec-tion for the eggs until they hatch into a larval form. The larvae are called nauplia (singular, nauplius). Successive molts and growth spurts produce the adult. The rate of growth varies with different species, and depends on the availability of food and the water temperature.

While the larvae of most crustaceans are pelagic fi lter feeders, the adults may develop into an astonishing variety of dig-gers, borers, or raptors while some remain fi lter feeders. The adult forms include, in addition to the usual motile animals, par-asites (copepods) and sessile (stationary)

forms (barnacles). Most crustaceans are grazing and scavenging animals, although the larger, more advanced decapods (lob-sters, crabs, shrimp) and stomatopods are more likely to be predators.

The crustacea and other arthropods seem to share an ancestor with annelids.

They were certainly present and well-dif-ferentiated in the Cambrian Period. Shells from this and other periods are well pre-served, and the resulting fossil record is quite complete. See Annelida, Anthrop-oda, crab, chitin, lobster, shrimp.

Ctenophora

A phylum of marine plankton abundant on the surface, but they may also found in deep water.

Seven orders and 19 families have been described. Ctenophora are macroplank-tonic, voracious, carnivorous eaters, using their radial arms, which have coeloblasts (adhesive cells), to trap food. Unlike the cnidarians that they resemble, they do not have stinging cells.

Ctenophora have biradial symmetry and a medusa-like three-layer body, the exterior and interior of which are com-posed of epithelial cells. The intermediate layer, the mesoglea, is gelatinous. Cteno-phores are characterized by their body shapes. They can be rather large: The gir-dle of Venus is a ribbon-like organism of transparent blue and green that grows to over 1 m (3 feet) in length. See Cnidaria, comb jellies, plankton.

Cubozoa

A class of the Cnidaria. These animals are in intermediate form that falls between the Hydrozoa and the Scypho-zoa. The eggs hatch into four-tentacled polyps that grow fairly rapidly into the adult form. When adult, they are a four-tentacled medusa with a “cube-shaped”

body. The Cubozoa are among the most toxic of marine organisms. See Antho-zoa, Cnidaria, ScyphoAntho-zoa, toxins.

currents

Parts of a fl uid body (air or water) moving continuously in a certain direction. In oceans, currents are respon-sible for the circulation of vast quantities

currents

of waters. They are caused by several fac-tors. The primary one is wind, which cre-ates a friction effect by pushing the mass of water. Another factor is temperature, because cold water, like cold air, fl ows toward the equator and sinks, since (like cold air) it is denser than warm water.

Local currents are produced by the activity of volcanoes, a sporadic phenom-enon; by river systems, whose effect is per-manent; and by tidal currents. The last are periodic. In general, oceanic circulation is horizontal. The movement of water is anticyclonic (clockwise) in the Northern Hemisphere. Water moves eastward at higher latitudes (i.e., the Gulf Stream) and returns (moves west) closer to the equator.

The east-to-west movement in the South-ern Hemisphere is cyclonic (counterclock-wise). This gyre is typical of the Atlantic and Pacifi c Oceans. It reverses itself semi-annually in the Indian Ocean because of the monsoon winds. The Antarctic region has a single current: the Antarc-tic Circumpolar Current. On the whole, less water is transported by gyre in the Southern Hemisphere than in the North-ern one. The speed of currents in open ocean is relatively slow, less than 1 knot (0.5 m/second), as opposed to the Gulf Stream, where it is 2 to 4 knots, or 1 to 2 m/second. The Pacifi c counterpart of the Gulf Stream is the Kuroshio. This current moves northeast out of the South China Sea to warm the Japanese islands and then moves east to the Aleutians. It, too, moves rapidly in comparison to the speed of the average ocean gyre.

In addition to surface currents, sub-surface equatorial currents such as the Cromwell are known. Deepwater circula-tion is slower than surface currents. It is the result of polar water sinking, a phe-nomenon observed in the Norwegian and Weddell Seas. The cold deepwater mass then moves toward the equator.

While this is the overall ocean pattern, it is very much infl uenced by conditions in particular locales. The conditions of tide, temperature of the abutting land-mass, and the size of the land formation

all have profound infl uences on deepwa-ter currents. The arrangement of conti-nents in the Northern Hemisphere makes it easier to see the circulatory patterns in the ocean, the gyres. Currents are respon-sible for the deposition of sediments on secondary coasts—those that are being eroded. Sediment can be moved along a coast by wave action in the surf zone, where there are breakers. This is long-shore drift. It moves the sand on a beach and may build up sand spits or bars at bay openings or barrier islands. This is the natural evolution of a coast. See Ant-arctic Current, coasts, Ekman Spiral, Equatorial Current, gyre, longshore current, rip current, wind.

cutter

A small ship built for speed. His-torically the cutter was a deep, narrow sailing vessel carrying a single mast rigged fore and aft, and had a long bowsprit.

Today the U.S. Coast Guard uses diesel-powered steel-hulled cutters that are 25 m (83 feet) or less long.

cuttlefi sh

A cephalopod, not a fi sh, of the order Sepioidea, related to the octopus and squid. Its origins are in the Miocene.

Cuttlefi sh comprise about 100 species of warm-water bottom dwellers. The cut-tlebone is really a shell that has become internalized. It acts as a fl exible support rod. Like all other mollusks, cuttlefi sh produce a calcareous shell by secretions from their mantle.

The various species of cuttlefi sh range in size from 2.5 to 9 cm (1 to 36 inches) long. They have eight arms, two longer tentacles, and a pair of lateral fringing fi ns. They eat small fi sh, crustaceans, and their own young, and are in turn fed upon by large fi sh and mammals. See Mollusca, octopus.

Cuvier, Georges Léopold Dagobert,

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