The Caribbean Sea is home to around 100 species of hard corals only a fraction of those inhabiting the Indo-Pacific region. Coral reefs in the Caribbean vary in appearance, from the dense and well-tended elkhorn thickets off Key West to the cacophony of coral species that crowd the reefs of Honduras's Bay Islands. The most common hard corals in the Caribbean are the finger or porites corals, the brain or
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rugosa corals, the branching staghorn or acropora corals, the star or montastrea corals, and the fire corals or hydrozoans that increasingly colonize reef areas where other coral species have been destroyed by dive tourism.
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This night-time photograph shows that a coral polyp, the transparent animal that builds the limestone rock we know as coral, is actually a very delicate living creature. Each tiny coral
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polyp takes years to secrete a thin layer of limestone on top of the stone layers secreted by previous generations. Divers and snorkelers who touch coral during the daytime, when it resembles stone, often find their fingers coated in a light slime—the living tissue of coral polyps from the ruptured animal that they have just destroyed.
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Soft Corals
The large, tuberous, stalked soft corals known in the Pacific are not found in the Caribbean. However, many other soft corals inhabit the region, including leathery-looking, spongelike colonies known, not surprisingly, as leather corals. These nondescriptly colored, unusually shaped species are rubbery to the touch. Unlike the hard corals, the animals that form soft corals do not secrete a protective shell of calcium
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carbonate, but they are filter feeders like the hard corals. Also like hard corals, soft corals are made up of thousands of tiny individual animals; however, the functions of the individuals vary with the colony. The featherlike tentacles of soft corals catch edible current-borne material as it passes by.
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Hydroids
The hydroids include several groups of animals. The best known are the fire corals or millepora, polyplike creatures that superficially resemble hard corals and secrete a calciferous shell. As they settle on the ocean bottom and form colonies, the millepora create curtainlike structures that resemble hard corals but flourish in areas where hard corals cannot. Like all members of this phylum, fire corals have a planktonic or medusa stage in which the juveniles float freely in water.
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Another group of hydroids form large colonial jellyfish, of which the Portuguese man-of-war is the best known in the Caribbean especially along Atlantic-facing beaches in the winter, when the jellyfishes are blown in from the Atlantic Ocean. A third and less-known group in the Caribbean is small and fernlike and can deal a
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powerful sting produced by a tiny barb coated with a toxin called a nematocyst. An individual animal may eject this toxin when its tissues come into contact with a foreign surface.
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Sea Fans
Sea fans or gorgonians are a large group of fanlike or brushlike polyp-based colonial Cnidarians that divers may mistake for plants. Their name derives from the protein material, called gorgonin, of which they are composed. Sea fans are so prolific in areas of clean water, such as the shallow reef-benches of Bonaire, that they dominate the reef. Sea fans vary in appearance from these large, fanlike, naked-tissued
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structures to species whose soft fronds are made up of what looks like hundreds of flower blossoms.
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Anemones
Incredibly, the anemone is a single animal called a polyp, with a central mouth and digestive system. The polyp's muscular tentacles house a stinging nematocyst, which the anemone uses to stun its prey. All of the tentacles work in unison to draw food toward its mouth, while the muscular and fleshy outer skin contracts over its meal. Anemones vary tremendously in size, shape, and preferred habitat; some
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live on shallow rocky surfaces, while others inhabit sandy bottoms. Despite misleading advertising and erroneous T-shirt slogans, the Caribbean's anemones are not host to resident anemonefishes, as are the anemones of the Indo-Pacific. In rare instances, one can observe a three-spot dascyllus, one of the damselfishes, living in association with an anemone. More common are
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the anemone shrimps that live within the protective tentacles of the anemone, very similar to the anemonefishes of the Pacific.
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Shrimps
The shrimps of the Caribbean are well known for their economic value; however, visitors to the coral reef typically encounter varieties of shrimp that are not important to the commercial fishing industry. Shrimps are a large and diverse group of the crustaceans that has evolved so its members can exploit almost every niche of the coral reef. Several groups of shrimp are commensal residents of sponges and
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anemones. They live on the surface of sponges or among the tentacles of anemones, where they forage for food and earn their keep by performing general cleaning of their hosts.
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Another shrimp group acts as cleaners of eels and other fishes. We have filmed shrimps actually walking into the mouths of large morays and picking at waste matter they find there. Several other kinds of shrimp live among the caves
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and crevices of every area of the reef, and typically are seen during the night when they leave their dens to feed. The type of shrimp most commonly seen by divers is this banded coral shrimp, which lives underneath corals. The tiny coral shrimp can easily be retrieved from its hiding places and held; unfortunately, almost any handling results in the shrimp losing its claw.
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Crabs
Like all crustaceans, crabs have hard exterior shells, jointed appendages, compound eyes, and antennae. Ranging from the tiny arrow crab to large specimens like the one shown here, crabs are found widely throughout the Caribbean, from intertidal zones to the deep ocean floor. The larger crabs of the Caribbean, such as this specimen from St. Lucia, are always interesting and generally harmless.
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Their formidable claws are capable of inflicting painful wounds—making them candidates for a diver's "don't touch" list. Crabs are omnivorous. They use their large claws for defense and mating, while their smaller, pincer-ended appendages, which lie under their mouths and are difficult to see, are used to gather and tear apart pieces of food.
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Hermit Crabs
The hermit is the crab best known to scuba divers. Hermit crabs inhabit the shells of gastropods and are most commonly seen at night. Because the size of the hermit crab is limited by the dimensions of the shell it occupies, it is always on the lookout for a new and larger shell. This comical-looking creature scuds about on the ocean bottom at night, walking along with its shell home on its back, retreating into the shell
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for protection at any sign of a threat. One hermit crab species has broad red-and-white stripes resembling those of a candy cane, with patches of bright blue on its body, hairy bristles that stand out from its legs, and articulated eye stalks that it waves about to view its environment.
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Lobsters
Lobsters are herbivores that live in a variety of habitats, from holes that they excavate in shallow sandy grass flats to crevices within the reef. Their most unusual behavior occurs with the changing seasons, when dozens or hundreds of lobsters migrate across sand flats in a single line to congregate for large-scale mating sessions at a central spot.
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The best-known lobsters of the Caribbean are the spiny lobsters, primarily because of their value as human food. Unlike Maine or rock lobsters (which are not found in the Caribbean), the spiny lobsters lack claws. They are considered a culinary treat by inhabitants of the region, to the point that overharvesting has nearly exterminated them in some areas.
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Another lobster group common in the Caribbean is the slipper lobster. Highly prized as food outside of the region, slipper lobsters are typically observed only at night.
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Sea Urchins
Three main groups of urchins inhabit the Caribbean: the long-spined, short-spined, and slate-pencil urchins. Bathers and shell collectors may also know a fourth type of urchin, the sand dollar flat, round creature that dwells in the sand flats and intertidal zones and whose white exoskeleton is collected especially around the Gulf and Florida coasts. The best-known species to scuba divers is the long-spined or diadema urchin,
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found throughout the Caribbean Sea. The diadema is a deservedly dangerous-looking animal whose spines can easily penetrate gloves or diving suits. Most beginning divers have had some experience with the short segments of these urchins' spines, which can lodge irretrievably in the divers' skin, where they dissolve over a long period of time.
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Thick-spined slate-pencil urchins can be handled, but during the day they wedge themselves into tight cracks of the reef and are difficult to retrieve. The short-spined urchins of the Caribbean typically bury themselves in the shallow sand flats where they live, becoming nearly invisible during the day. Most urchins leave their protected areas and move about to hunt for food at night. Like all echinoderms, urchins have a radial or five-part symmetry, as well as a
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central mouth and stomach. Tiny hairs pass food along the length of their bodies, drawing particles into the mouth.
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Sea Stars
The radial symmetry of the echinoderms is most evident among the sea stars of the Caribbean, which typically have five legs. Caribbean sea stars range from tiny jewellike creatures to large bright-red specimens found in the Florida Keys that can measure nearly a foot across. Sea stars have tiny tentacles called peduncles; these tubelike fleshy appendages perform several functions, including acting as feet.
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Turn over any sea star and look quickly at the central dividing line along each leg; you will observe hundreds of peduncles being withdrawn to the safety of the animal's hard exoskeleton. A sea star uses these "feet" both to propel itself and, like the sea urchin, to transport food to its mouth, which is located at the intersection of its five legs. One group of sea stars, the pincushion stars, have evolved so that
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their legs have disappeared and the central part of their bodies are several inches thick.
Sea stars are omnivorous and will eat gastropods, dead fishes, live corals (the crown-of-thorns sea star, deadly to corals, is found only in the Indo-Pacific), and even other sea stars.
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Basket Stars
Basket stars derive their name from the convoluted tentacles that constitute their legs, which they wrap up in tight knots during the day when they hide. At night, like the crinoids or feather stars, the basket stars walk to prominent spots on the reef and unfurl their thousands of short stocks. And like the brittle stars, basket stars retreat at the first contact with any light; although they cannot move as fast as the
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brittle stars, they seem to disappear within seconds of being illuminated. They use their unfurled legs to filter passing water for pieces of food, which tiny tentacles then pass to their central body core. When fully extended, a basket star may measure 1 meter across.
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Sea Cucumbers
Sea cucumbers are one of the most important invertebrate groups in the coral reef system first, because they process vast amount of material on the sea floor into sand; and second, because they are an essential food source for the millions of Chinese for whom sea cucumber (also known as beche de mer) is a traditional holiday food. The dried skins of the sea cucumber are sold to Chinese merchants by the tens of thousands, resulting in the species' near-extinction in some areas and in irreparable harm to the reef.
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Some types of sea cucumbers are so slow-moving that they do not appear to be living, while others are so active during their feeding cycle that it is hard to recognize them as invertebrates. If violently disturbed, some species in the Caribbean will eject their intestines in an effort to distract
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their attacker with a meal while they move away; they survive this seemingly gruesome process and grow new intestinal organs.
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Brittle Stars
All brittle stars have five legs. It was originally thought that they could not tolerate light; however, some species have been found in open sunlight. The real reason for their furtive nature now appears to be strictly self-preservation. Brittle stars have a central bony disk that houses their central mouth and organs. Their slight, delicate, hairy legs are quite flexible; they use them to pull their central disk
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from spot to spot. Some of the brittle stars can move quite rapidly. Even when they are seen at night, it is unusual to observe these members of the echinoderms for any length of time.
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Gastropods
For many people, the gastropods (also known as sea snails or sea slugs), are the most recognizable ocean creatures after the bony fishes. Partly because of the tragically destructive trade in seashells, these important animals are disappearing on many coral reefs. The best-known species in the Caribbean are the several types of conches, including the queen and wing-tip conches, that are important food
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sources. The snaillike conches secrete a material that hardens to form the lovely shells so prized by collectors and sought in ancient times by skilled tradesmen who carved cameos on their surfaces. The huge roadside piles of bleached conch shells throughout the Caribbean make a sad statement about our overuse of valuable ocean resources. Another signature species of gastropod in the Caribbean, the
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flamingo tongue shell often lives on the common blue sea fan or other gorgonians. The flamingo has an extensive mantle, or tissue flap, that when undisturbed they extrude over the surface of their shell. Unfortunately, this lovely, tigerlike mantle is the flamingo's undoing, as it makes the creature almost irresistible to shell collectors and novice divers. When dead, however, the
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flamingo becomes a rather less beautiful pink shell. Like all molluscs, the gastropods are highly evolved and intelligent animals. The conch has two independently movable eyes that grow on the end of long stalks, a fleshy muscular foot that excretes a mucous slime upon which the creature moves, and a radula or tongue with which it rasps food—typically protein-rich phytoplankton—from the surfaces of plants.
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Nudibranchs
Nudibranchs are an order of sea slug closely related to the gastropods, with the distinction that only one of the five nudibranch orders has an external shell. Few of the exotic species, such as the large, red Spanish dancer; the elaborately lobed opistobranch nudibranch; or the large sedentary species known in the Indo-Pacific are found in the Caribbean. However, several of the warty
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(or phyllidia) species inhabit the Caribbean. At first glance, a nudibranch may appear to be part of the sponges upon which many of them feed, but a closer examination allows a diver to see the little muscular foot on the animal's underside. Their Latin name translates as "naked lung" and refers to those orders of nudibranch that have external gills they can extend or withdraw into their body.
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Bivalves
Unlike gastropods, which have a single shell, a bivalve has two hinged shells and a strong central adductor muscle that it uses to pull the two halves together. Bivalves include scallops, clams, and oysters; the largest members of this class, the giant sea clams, are not found in the Caribbean.
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Bivalves range in size and shape from the pin scallop, which grows vertically in sandy, grassy reef flats, to the beautiful spondyllus and flame scallop shells known throughout the world.The flame scallop shown here typically lives within the cracks of reefs, but it can propel itself around the reef to feed by pulling the two halves of its shell together quickly to force a stream of water out of its shell. Bivalves are filter feeders; a member will moor itself to a hard substrate with its muscular foot, which has evolved to let it grip
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a surface by creating a vacuum underneath.
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Octopus
The subgroup of molluscs collectively known as cephalopods includes the squid and octopus, as well as two other groups not found in the Caribbean: the cuttlefish and the nautilus. Cephalopods have the most highly evolved nervous and brain systems of any invertebrate, and it has been suggested that their use of color and body shape constitutes a form of language. In addition, their bodies have
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evolved to allow them an extraordinary degree of flexibility in exploiting their habitat. They hunt with deadly efficiency. Several species of both squid and octopus are found in the Caribbean. Squids live in the open water column where they hunt, although they may visit the reef or the ocean floor for this purpose, too. The octopus's habitat range is limited to the sea bottom and the coral reef. Both squids and octopuses
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have adhering suckers that can grip tenaciously by creating a vacuum under the surface of the sucker discs. Both groups are also able to eject ink to distract potential predators. Octopuses and squids reproduce through copulation, and both groups have complex eyes that are thought to provide highly detailed vision of their environment. The poisonous species of octopus found in the Indo-Pacific
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do not inhabit the Caribbean. However, the Caribbean octopuses are nevertheless capable of inflicting painful wounds with their hard, beaklike mouths—yet another reason that divers should not touch these gentle, intelligent creatures.
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Sponges
Sponges, like the crinoids, are an ancient group of organisms. They are found in every ocean and in all biological niches. Their variety of forms seems endless; the best-known species in the Caribbean are the tube, vase, and basket sponges, so named because of their shapes. Like all sponges, they are filter feeders. Water flows through a sponge's thousands of tiny channels or is pulled through the channels by
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the beating of microscopic hairlike tentacles of cilia. This flow of water provides a constant source of organic material and oxygen on which the cells of the sponge live. The basket sponges of the Caribbean, usually brown in color, can grow to truly prodigious sizes—large enough, in fact, to hold a scuba diver! The tube sponges are typically colored yellow or orange and can grow to several feet in length.
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One group of vase sponges is luminescent blue; this striking color perhaps helps photosynthesis in the deeper waters where they grow.
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Taxonomy
Taxonomic classification is the process that identifies evolutionary relationships of organisms. An organism's shape, behavior, size, and biochemistry determine which naturally occurring group it belongs to. This phylogenetic tree shows the possible relationships among the different major marine phyla. The
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phyla low on the tree, such as sponges, are judged to be more primitive, and they appear earlier in the fossil record. The phyla higher on the tree are more advanced in their structure and appear later in the fossil record. Phylogenetic trees (cladograms) are derived by analyzing shared specializations,
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a subject called cladistics. Species are classified using a naming system that follows a special hierarchy: kingdom, phylum, class, order, family, genus, and species. This classification method allows us to track the evolutionary relationships among organisms.
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These categories start with the broadestæthe kingdom nameæand end with the most specific, the species name. Phyla and class are broad terms used in this section to show examples of the commonly occurring marine phyla and classes.
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Phylum: Chordata
Subphylum: Vertebrata
Class: Chondrichthyes (sharks, skates, and rays)
This class of vertebrates is easily distinguished from the bony fishes because of their distinctive body profiles. Other differences are that their skeletons are made of cartilage rather than bone, they lack a swim bladder, and they have internal fertilization in which a modified process on the pelvic fins serves as the copulatory apparatus.
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Class: Mammalia (whales and dolphins)
Dolphins, whales, and porpoises are all members of the order Cetacea, which includes about 76 species. The Cetaceans are descendants of land animals that entered the sea about 55 million years ago.
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Class: Osteichthyes (bony fishes)
Bony fishes make up a complex and diverse class that has adapted itself to a wide range of habitats in both freshwater and marine environments. More species of bony fishes exist than do all other vertebrate groups combined.
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Class: Reptilia (marine turtles, iguanas, and crocodiles)
Relatively few reptiles live in marine environments; the most common are the marine turtles and the sea snakes. A few species of iguanas and crocodiles also inhabit coastal waters.
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Phylum: Chordata
Subphylum: Urochordata
Class: Ascidiacea (sea squirts)
Despite their appearance, Ascidians are the invertebrates most closely related to vertebrates. Occurring in a wide range of colors and sizes, sea squirts have two openings through which they siphon water. They also have a circulatory system, stomach, and a branchial sac for gas exchange.
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Phylum: Echinodermata
Class: Asteroidea (sea stars)
The sea stars are good examples of the five-part radial symmetry that all echinoderms share. Most but not all sea stars have five arms that can vary in color and length. Sea stars are predators and detritus eaters that crawl with tiny tube feet located on the underside of their arms.
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Class: Crinoidea (feather stars and sea lilies)
Crinoids are plankton feeders that cling to the reef and use their arms to filter food from the water. They can have anywhere from 5 to 200 arms, depending on the species. They occur in a wide variety of colors, and some are capable swimmers.
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Class: Echinoidea (sea urchins and sand dollars)
Sea urchins are herbivores or sediment eaters with spines that vary in length from short and fairly blunt to long and very sharp. Some species have venomous spines that can cause nasty—even fatal—wounds.
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Class: Holothuroidea (sea cucumbers)
Sea cucumbers occur in a variety of shapes, from long sluglike species to gracefull, tentacled filter feeders. Some species of Holothuroids are capable of expelling internal organs as a defensive mechanism. (These organs are later regenerated.)
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Class: Ophiuroidea (brittle stars and basket stars)
Brittle stars eat small organisms and detritus, and they generally have five arms. Most brittle stars hide during the day and come out at night to feed, entwining themselves on gorgonians and sponges.
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Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca (lobsters, shrimp, and crabs)
Malacostraca is the most commonly seen class of Crustacea: lobsters, shrimp, and crabs. Crustaceans have jointed appendages, an exoskeleton, and two pairs of antennae. They feed on small organisms and detritus.
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Phylum: Annelida
Class: Polychaeta (segmented worms)
Many types of segmented worms occur in marine environments. The most commonly seen is the Christmas tree worm (above). Segmented worms differ from other worms in that their bodies are divided into a linear series of similar segments.
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Phylum: Platyhelminthes
Class: Turbellaria (flatworms)
Flatworms are as colorful and fascinating as the nudibranchs, which with they are often confused. Most commonly seen crawling along the bottom, flatworms are also able to swim by undulating their flat, thin bodies in the water.
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Phylum: Mollusca
Class: Bivalvia (clams, oysters, mussels, and scallops)
Bivalves are molluscs that have two shells joined by a powerful muscle. Most are filter feeders that strain food from the water. They occur at many depths, from the intertidal zone to about 5,000 meters.
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Class: Cephalopoda (Nautilus, squid, and octopus)
Cephalopods are the most sophisticated class of molluscs. Most have glands that expel a cloud of black inklike substance when they are threatened. Squids and cuttlefishes use a jet of water to propel themselves through the water.
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Class: Gastropoda (snails, nudibranchs, and sea hares)
This class includes both freshwater and terrestrial species. Most gastropods feed on detritus and algae, and some are predators. Gastropods are generally identified as having only one shell, as do the snails. But some gastropods, such as the nudibranchs, lack a shell altogether.
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Class: Polyplacophora (chitons)
Chitons live in the tidal and subtidal zones of all the world's oceans. Most are algae eaters that firmly attach themselves to rocks and move very slowly. They are well protected by the eight overlapping plates that cover their entire body. There are around 500 species of chiton.
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Phylum: Cnidaria
Class: Anthozoa (corals, corallimorpharians, sea fans, sea anemones, zoanthids, and black corals)
As their name translates, these are the flowers of the sea. The many different types of corals and anemones all have body forms based on a polyp. Calcareous deposits from some corals make up the backbone of many reefs. This is by far the most diverse class of Cnidarians.
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Class: Hydrozoa (hydroids)
Hydroids vary in shape and color—from the bushy plumes often confused with algae to the majestic Portuguese man-of-war. Some species, such as the fire corals, have calcareous skeletons. Hydroids are carnivores and feed on planktonic animals.
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Class: Scyphozoa (jellyfishes)
The Scyphozoa class includes some of the most fascinating and beautiful animals in the oceans. Likes hydroids, jellyfishes have nematocysts that can deliver painful stings. They range in size from a few inches to several feet in diameter.
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Phylum: Porifera
Class: Demospongiae (tube sponges, vase sponges, and barrel sponges)
Sponges are sedentary filter feeders whose bodies pass water through a network of canals into chambers where food is filtered out; the water is then expelled. Sponges appear in many sizes, colors, and shapes and are the oldest group of multicellular animals.
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Belize
Belize, a former British colony surrounded by Spanish-speaking countries, has become one of the most popular new diving areas in the Caribbean. Development in Belize has been slower than throughout the rest of the region, and today it seems populated mostly with tourists from the United States. The barrier reef that flows along Belize’s eastern shore heavily promoted as the second longest in the world actually bears little resemblance to Australia’s Great Barrier Reef, with its rich diversity of flora and fauna.
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Nevertheless, some of the Caribbean’s best diving can be found there. The finger canyons that have cut into the shoreline for some 10,000 years form countless deep and narrow marine canyons that today provide protection for larger species of fish. Channels that periodically cut the fringing reef, the site of fierce tidal current exchanges, are home to large dense schools of fishes. Despite significant pollution from untreated shore waste, the water beyond
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the fringing reef is so clean that even the sensitive spotted dolphins are commonly heard (and sometimes seen) in the area. There are also several “blue holes “deep, bell-shaped depressions, relatively devoid of life but endlessly fascinating to divers along Belize’s reef. These holes, the result of limestone erosion from rainwater when the sea level was much lower, are found in many areas of the Caribbean, including the Bahamas and Jamaica. A word of warning: Diving conditions in
