Adélie penguins are small Antarctic penguins with black heads, white bellies, and bright white rings around their eyes. They live around Antarctica, nest on rocky ice-free ground, and dive for krill, fish, and other small sea animals.

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African penguins are flightless seabirds from the coasts of South Africa and Namibia. They have black-and-white feathers, pink patches above the eyes, donkey-like braying calls, and a conservation story that needs urgent help.

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Albatrosses are giant seabirds with long narrow wings built for gliding over oceans. They spend much of life at sea, feed on squid and fish, and return to remote islands to nest and raise chicks.

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Angelfish is a name used for different beautiful fish, but the popular freshwater angelfish is a tall, graceful cichlid from tropical South America. It has a flat body, long fins, and dark vertical bands that help it blend among plants and roots.

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Anglerfish are strange ocean fish famous for using a built-in fishing lure to attract prey. Many well-known anglerfish live in the deep sea, where darkness, pressure, and weird adaptations create a truly alien ocean world.

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Auks are diving seabirds that live in northern oceans. They have short wings, strong swimming skills, and thick bodies that help them dive underwater for fish, crustaceans, and other sea foods.

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Barnacles are ocean crustaceans that spend adult life attached to rocks, shells, boats, piers, whales, or other surfaces. They may look like tiny shells or bumps, but they are relatives of crabs, shrimp, and lobsters.

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Barracudas are fast, powerful fish known for long bodies, sharp teeth, and lightning-quick attacks. They live in warm oceans around reefs, seagrass beds, and open water, where they hunt fish and other prey.

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The basking shark is the second-largest living fish, after the whale shark. This enormous but harmless shark cruises through temperate oceans with its mouth wide open, allowing water to flow across bristle-like gill rakers that trap tiny zooplankton. Its scientific name is Cetorhinus maximus, and despite the dramatic gape, it does not hunt people or large marine animals.

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Beluga whales are small white whales that live in cold Arctic and subarctic waters. They are social, vocal, and famous for their rounded melon heads, flexible necks, and many whistles, clicks, chirps, and squeals.

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Blobfish are deep-sea fish with soft jellylike bodies that help them live under strong ocean pressure. They look much more fish-shaped in the deep sea, but when brought to the surface, pressure changes can make them look blobby.

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Blue tangs are bright tropical reef fish with beautiful blue coloring and a yellow tail in many well-known species. They belong to the surgeonfish family, which is named for sharp spines near the tail.

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Blue whales are the largest animals on Earth. These gentle ocean giants are mammals, breathe air through blowholes, use baleen to filter tiny krill, and can make deep sounds that travel through the sea.

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Blue-ringed octopuses are small ocean octopuses with bright blue warning rings. They may look beautiful, but they are extremely venomous, so people should never touch them and should admire them only from a safe distance.

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Bluefin tuna are powerful ocean fish built for speed, distance, and life in the open sea. They have streamlined bodies, crescent-shaped tails, warm swimming muscles, and a long migration story that stretches across huge ocean spaces.

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Boobies are tropical seabirds known for strong flight, webbed feet, pointed wings, and dramatic plunge-dives into the ocean. Some species, like the blue-footed booby, are famous for bright feet and funny courtship dances.

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Bowhead whales are huge Arctic baleen whales with dark bodies, massive bow-shaped heads, thick blubber, and giant mouths. They live in icy northern waters and can survive for an extremely long time.

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Boxfish are unusual reef fish with stiff, box-like bodies covered by hard bony plates. They swim slowly using small fins, often looking like tiny floating boxes as they explore reefs, lagoons, and sandy ocean areas.

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Brittle stars are ocean invertebrates related to sea stars. They usually have a small central disk and five long flexible arms that can wriggle, crawl, break off, and regrow if needed.

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Bull sharks are strong, stocky sharks famous for living in both salt water and freshwater. They can swim into rivers, use shallow coastal nursery areas for young sharks, and hunt with sharp senses, but wild sharks should always be treated with respect.

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Butterflyfish are small, bright reef fish that live in warm tropical oceans. Their flat bodies, bold stripes, tiny mouths, and eye-like spots help them dart around coral reefs while searching for small animals, coral polyps, and other reef foods.

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Chinstrap penguins are small Antarctic penguins named for the thin black line under the chin. They breed in noisy colonies on rocky Antarctic and subantarctic islands and feed mostly on krill and other small ocean animals.

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Clownfish are bright reef fish with orange, white, yellow, or black patterns. They are famous for living safely among sea anemone tentacles in warm shallow reefs of the Indian and Pacific oceans.

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Cod are cold-water ocean fish known for speckled bodies, pale side lines, three dorsal fins, and a small chin barbel. The name cod often refers to Atlantic cod, but there are several cod species in the cod family.

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Coelacanths are rare deep-water fish with fleshy lobe-like fins and an ancient family history. Scientists knew them from fossils and were amazed when a living coelacanth was found off South Africa in 1938.

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The colossal squid, Mesonychoteuthis hamiltoni, is a massive deep-sea cephalopod found only in the Southern Ocean around Antarctica. It is shorter than the longest giant squid but has a broader, heavier body and is the heaviest known invertebrate. Adults live in freezing water at depths of roughly 1,000 metres or more, where direct observation is extraordinarily difficult. Much of what scientists know comes from rare specimens and beaks recovered from sperm-whale stomachs.

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Comb jellies are soft, transparent ocean animals in the phylum Ctenophora. They are not jellyfish, even though both groups have watery bodies and drift through the sea. Most comb jellies swim by beating eight rows of fused cilia called comb plates. These moving rows scatter light into rainbow colors, while many species can also produce a separate blue-green glow through bioluminescence. Body shape, tentacles, depth, diet, and reproduction vary widely across the group.

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The common seal, Phoca vitulina, is also called the harbor seal or harbour seal. It is a small true seal found around temperate and Arctic coasts of the Northern Hemisphere. Common seals have rounded heads, V-shaped nostrils, no external ear flaps, short front flippers, and individually patterned spotted coats. They hunt underwater but regularly haul out on rocks, sandbanks, mudflats, beaches, and ice to rest, give birth, nurse pups, and molt.

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The Common Tern, Sterna hirundo, is a graceful waterbird that breeds across large parts of Europe, Asia, and North America. It nests beside coasts, lakes, and rivers and spends the nonbreeding season along warmer seas. Breeding adults have a black cap, pale gray body, red-orange legs, a red bill with a dark tip, narrow pointed wings, and a deeply forked tail. They hover above water before plunging after small fish.

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Cone snails are marine snails with beautiful cone-shaped shells and powerful venom. They are slow-moving predators that use a harpoon-like tooth to catch prey, so wild cone snails should never be picked up or handled.

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Corals are tiny marine animals called polyps. Many coral polyps live together in colonies, build hard limestone skeletons, and create coral reefs that become busy underwater homes for fish, crabs, sea turtles, and many other ocean creatures.

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Cowfish are boxfish relatives named for horn-like spines on the head of some species, especially the longhorn cowfish. These odd reef fish have stiff armored bodies, small mouths, slow hovering movement, and cheerful yellow or spotted patterns.

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Crab is a common name used mainly for true crabs in the infraorder Brachyura, a huge group of decapod crustaceans with broad bodies and short abdomens folded beneath the shell. True crabs inhabit every ocean and have also colonized rivers, lakes, caves, mangroves, beaches, forests, and other land habitats. They range from tiny pea crabs to Japanese spider crabs with enormous leg spans. Hermit crabs, king crabs, porcelain crabs, and several other crab-shaped animals belong to different branches.

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Crown-of-thorns starfish are large spiky sea stars found on coral reefs. They eat coral polyps and have venomous thorn-like spines, so they should be watched from a safe distance and never touched.

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Cuttlefish are clever sea animals related to octopuses and squid. They can change color and pattern, use ink to escape, and have a special internal shell called a cuttlebone.

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Decorator crabs are marine crabs that hide by attaching bits of algae, sponge, shell, or other ocean material to their bodies. Their disguise can help them blend into reefs, tide pools, or seafloor habitats.

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Dolphins are smart, social marine mammals known for jumping, clicking, whistling, swimming fast, and using echolocation to find their way underwater. They breathe air, live in groups, and give birth to live babies called calves.

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Dugongs are gentle marine mammals often called sea cows. They live in warm coastal waters, graze on seagrass, breathe air at the surface, and use a whale-like fluked tail to swim.

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Elephant seals are enormous true seals in the genus Mirounga. Two living species exist: the Northern Elephant Seal, Mirounga angustirostris, of the eastern North Pacific, and the Southern Elephant Seal, Mirounga leonina, of subantarctic and Antarctic waters. Adult males develop an inflatable trunk-like nose called a proboscis and can be several times heavier than females. Elephant seals spend most of the year at sea, making repeated deep dives for squid and fish before returning to land for breeding and molting.

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The Fin Whale, Balaenoptera physalus, is a sleek baleen whale found in every major ocean. It is the second-largest living animal after the Blue Whale and can grow longer than a large passenger airplane. Fin Whales have long streamlined bodies, narrow V-shaped heads, tall curved dorsal fins, pale chevrons behind the head, and unusually asymmetrical jaw coloring. They feed by lunging through krill and schools of fish, then filtering prey through hundreds of baleen plates.

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Flounders are flatfish that live on or near the seafloor. They hatch looking like ordinary fish with one eye on each side, but as they grow, one eye moves to the other side and the fish begins resting flat on the bottom.

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Flying fish are ocean fish with large wing-like fins that let them glide above the water. They do not flap like birds, but they can launch from the sea and sail through the air to escape predators.

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Frigatebirds are large tropical seabirds with huge wings, long forked tails, hooked bills, and amazing gliding skills. Male frigatebirds are famous for inflating bright red throat pouches during courtship displays.

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Gannets are large fish-eating seabirds in the genus Morus and the family Sulidae. Three living species exist: the Northern Gannet of the North Atlantic, the Cape Gannet of southern Africa, and the Australasian Gannet of Australia and New Zealand. Adults are mostly white with black flight feathers, long pointed wings, streamlined bodies, strong webbed feet, and dagger-like bills. Gannets are famous for folding their wings and plunging from the air into the sea to catch schooling fish and squid.

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Gentoo penguins are bold penguins with bright orange bills, orange feet, and a white stripe across the head. They breed on subantarctic islands and parts of the Antarctic region, dive for food, and are famous for fast underwater swimming.

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Giant clams are huge reef mollusks with two heavy shells and colorful mantles. They live in warm Indo-Pacific coral reefs and share a clever partnership with tiny algae that help feed them with sunlight-made food.

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Giant isopods are enormous deep-sea crustaceans that look like huge pill bugs from the ocean floor. They have armored plates, 14 walking legs, big eyes, long antennae, and a scavenger lifestyle in the dark deep sea.

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Giant squid are mysterious deep-sea animals with huge eyes, eight arms, two extra-long tentacles, a beak, and a soft body. They live far below the ocean surface, where humans rarely see them alive.

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The goblin fish, often written as goblinfish, is an odd-looking scorpionfish relative found in southern Australian marine waters. It has a lumpy body, strong camouflage, and venomous fin spines, so it should be admired from a safe distance.

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Goblin sharks are strange-looking deep-sea sharks with long flat snouts, soft bodies, sharp teeth, and jaws that can shoot forward to grab prey. They live far below the ocean surface and are rarely seen by people.

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Gobies are usually small fish found around shores, reefs, rivers, and sandy bottoms around the world. Many live near the bottom, and some have fused pelvic fins that work like a small suction cup.

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The Gray Whale, Eschrichtius robustus, is a large baleen whale found regularly only in the North Pacific Ocean. It is the sole living species in the family Eschrichtiidae. Gray Whales have mottled gray skin, broad paddle-shaped flippers, no true dorsal fin, and a row of small back bumps called knuckles. They are famous for feeding along the seafloor, migrating close to shore, and raising calves in warm shallow lagoons. Two main populations remain: the much larger eastern North Pacific population and the far smaller western North Pacific population.

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Great white sharks are large predatory fish with powerful bodies, sharp teeth, strong tails, and amazing senses. They are important ocean hunters, but they are also often misunderstood because of scary movies and myths.

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Green sea turtles are large hard-shelled sea turtles that live in warm ocean waters. Adults mostly eat seagrass and algae, and females return to sandy beaches to lay eggs.

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The Grey Seal, Halichoerus grypus, is a large true seal found around the North Atlantic Ocean and Baltic Sea. It is also spelled Gray Seal in American English. Adult males grow much larger than females and develop long convex noses that inspired the scientific name meaning hooked-nosed pig of the sea. Grey Seals rest and breed on beaches, rocky islands, reefs, sea ice, caves, and sandbars, then travel offshore to hunt fish, squid, octopuses, and crustaceans.

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The Guillemot, Uria aalge, is a large auk also called the Common Guillemot in Britain and the Common Murre in North America. It breeds around the North Atlantic and North Pacific on crowded sea cliffs, rocky islands, stacks, and ledges. Adults have chocolate-brown or nearly black upperparts, white underparts, narrow pointed bills, short legs set far back on the body, and compact wings that work in both air and water. Guillemots spend most of the year at sea and return to land mainly to raise a single chick.

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Halibut are large flatfish that live on or near the ocean floor in cold northern waters. Adult halibut have both eyes on one side of the head, which helps them lie flat and watch for prey above the sandy or muddy bottom.

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Hammerhead sharks are famous for their wide hammer-shaped heads. These unusual heads place their eyes and nostrils far apart, helping hammerheads sense the ocean around them as they swim.

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The Harp Seal, Pagophilus groenlandicus, is a true seal of the Arctic and North Atlantic oceans. Adults have pale silver-gray bodies, dark faces, and a black harp-shaped or saddle-like marking across the back and sides. They migrate between feeding seas and drifting pack-ice breeding grounds. Three main populations or stocks breed in the Northwest Atlantic, Greenland Sea, and White Sea or Barents Sea. Females give birth to one pup on the ice and nurse it for less than two weeks before returning to sea.

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Hawksbill sea turtles are beautiful reef turtles with pointed beak-like mouths and patterned shells. They live in warm oceans, help coral reefs by eating sponges, and are critically endangered, so protecting beaches and reefs matters.

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Hermit crabs are crustaceans with soft curved abdomens that need protection. Many live inside empty snail shells, changing to larger shells as they grow, while using pincers, antennae, legs, and careful shell shopping to survive.

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Horseshoe crabs are ancient-looking sea animals with hard horseshoe-shaped shells, long pointed tails, and blue blood. Even though they are called crabs, they are not true crabs and are more closely related to spiders and scorpions.

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Humpback whales are large ocean mammals famous for their long flippers, haunting songs, huge leaps, and clever feeding tricks. They are baleen whales that filter small sea animals from the water.

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Japanese spider crabs are giant ocean crabs with extremely long legs, spiky shells, and a spider-like look. They live in Pacific waters near Japan and are famous for having the largest leg span of any living crab.

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Jellyfish are soft sea animals with jellylike bodies, no bones, and trailing tentacles. They drift through oceans around the world and use stinging cells to catch tiny prey.

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King penguins are tall penguins with orange patches on the head and chest. They breed on subantarctic islands, gather in huge colonies, dive for fish and squid, and raise fluffy brown chicks during a long breeding cycle.

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Krill are tiny shrimplike crustaceans that live in the ocean, often in huge groups. They may be small, but they are one of the most important foods for whales, seals, penguins, fish, squid, and many other marine animals.

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Leafy sea dragons are amazing ocean fish that look like drifting seaweed. They have leafy body parts, long snouts, tiny fins, and beautiful camouflage that helps them hide among seagrass and kelp along southern Australia.

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Leatherback sea turtles are the largest sea turtles and the only sea turtles without a hard shell. They have a flexible leathery carapace, huge front flippers, and travel across oceans to find jellyfish and nesting beaches.

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The Leatherback Turtle, Dermochelys coriacea, is the world's largest living turtle and the only surviving sea turtle without a hard, scaly shell. Its streamlined black body is covered by tough rubbery skin over thousands of tiny bones, with seven long ridges running down the back. Leatherbacks cross the Atlantic, Pacific, and Indian oceans, dive deeper than any other turtle, and travel between tropical nesting beaches and cold jellyfish-rich feeding seas. The species is globally Vulnerable, while several regional populations are Endangered or Critically Endangered.

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The Leopard Seal, Hydrurga leptonyx, is a large solitary true seal of the Antarctic pack ice and Southern Ocean. It has a long muscular body, powerful front flippers, a broad reptile-like head, enormous jaws, and dark spots across a pale underside. Females are generally larger than males. Leopard Seals are unusual predators because the same mouth can seize penguins, fish, squid, and young seals while interlocking back teeth strain tiny krill from seawater. The species is currently assessed as Least Concern, but its abundance is difficult to measure across moving pack ice.

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Limpets are cap-shaped sea snails that cling tightly to rocks and other hard surfaces. This page focuses on true limpets in Patellogastropoda, an accepted major group of marine gastropods. The word limpet is also used for unrelated snails that independently evolved similar cone-shaped shells, including keyhole limpets and air-breathing false limpets. True limpets usually have one low conical shell, a broad muscular foot, a scraping ribbon called a radula, and adaptations for surviving waves, drying air, changing temperatures, and hungry predators.

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Lionfish are beautiful but venomous reef fish with bold stripes, long fin spines, and wide fan-like pectoral fins. They are native to Indo-Pacific waters, but some species have become invasive in the western Atlantic, Caribbean, and Gulf of Mexico.

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Little blue penguins, also called little penguins or kororā, are the world’s smallest penguins. They have blue-gray backs, white bellies, and coastal lives where they swim for fish by day and often return to shore after dark.

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Lobsters are hard-shelled crustaceans that live mostly on the sea floor. Many true lobsters have large claws, long antennae, walking legs, strong tails, and a tough outer shell that they must molt as they grow.

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Loggerhead sea turtles are ocean reptiles named for their large heads and strong jaws. They use those jaws to crush hard-shelled prey such as whelks, conchs, crabs, and other seafloor animals.

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Mahi-mahi are bright open-ocean fish also called dolphinfish or dorado, but they are fish, not dolphins. They are famous for electric blue-green backs, golden sides, fast growth, and strong swimming near the ocean surface.

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Mako sharks are sleek open-ocean predators in the mackerel shark family. There are two living species: the shortfin mako, Isurus oxyrinchus, and the less familiar longfin mako, Isurus paucus. The shortfin mako is famous as the fastest known shark, while the longfin mako has much longer pectoral fins and is adapted for a somewhat slower cruising lifestyle. Both species face serious pressure from fishing and accidental capture.

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Manatees are gentle aquatic mammals often called sea cows. They have round bodies, paddle-shaped tails, flippers, whiskery faces, and big lips that help them eat aquatic plants.

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Mandarin fish, also called mandarinfish, are tiny jewel-colored reef fish from the Pacific. They are dragonets, not true gobies, and they move slowly among coral rubble while looking for tiny animals to eat.

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Manta rays are graceful ocean fish related to sharks and rays. They glide through warm waters using giant wing-like fins and filter tiny plankton and small animals from the water.

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Mantis shrimp are colorful marine crustaceans known for amazing eyes and super-fast hunting arms. Some use club-like arms to smash prey, while others use sharp spear-like arms to grab fish and other small ocean animals.

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Marine iguanas are unusual reptiles from the Galapagos Islands. They are the only modern lizards that regularly forage in the sea, where they swim and dive to eat algae growing on rocks.

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Marlins are large open-ocean billfish with long spear-like bills, strong bodies, and powerful swimming skills. Different marlin species include blue, black, striped, and white marlins, and many are famous ocean predators.

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Moon jellies are pale translucent jellyfish often seen in coastal waters. They have soft bell-shaped bodies, short tentacles, four petal-like shapes inside, and a gentle pulsing swim that looks like a floating moon.

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Moray eels are long, snake-like fish that live in warm ocean reefs and rocky hiding places. They have sharp teeth, strong jaws, smooth mucus-covered skin, and a secret second set of jaws in the throat that helps pull food down.

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Mussels are bivalve mollusks with two shells and soft bodies inside. Some live in the ocean attached to rocks by strong threads, while freshwater mussels often live partly buried in river or lake bottoms.

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Narwhals are small Arctic whales famous for their long spiral tusks. They are sometimes called unicorns of the sea, but the tusk is not a horn. It is actually a special tooth.

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Nautiluses are ancient-looking ocean animals with soft bodies, many tentacles, and beautiful spiral shells divided into chambers. They are cephalopod mollusks, which means they are related to octopuses, squid, and cuttlefish.

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Nudibranchs are colorful sea slugs that live in oceans around the world. They are soft-bodied marine mollusks, often without shells as adults, and many use bright colors, strange shapes, gills, cerata, and chemical defenses to survive.

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Nurse sharks are slow-moving sharks that often rest on the ocean bottom during the day and hunt at night. They have rounded heads, small mouths, barbels near the nose, and strong suction feeding skills.

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Ocean sunfish, also called mola mola, are huge flat ocean fish that look a little like a giant swimming head. They are among the largest bony fish and can be seen basking near the surface in warm and temperate seas.

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Octopuses are clever sea animals with soft bodies, eight arms, strong suckers, large eyes, and amazing camouflage. They are mollusks, not fish, and many can squirt ink to confuse predators.

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Orcas, also called killer whales, are powerful ocean mammals with black-and-white bodies, strong fins, sharp teeth, and close family groups called pods. Even though people call them whales, orcas are actually the largest members of the dolphin family.

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Oysters are ocean mollusks with two shells called valves. Many oysters live attached to hard surfaces, filter tiny food from seawater, and can build rough reefs that shelter small ocean animals.

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Parrotfish are colorful reef fish named for their parrot-like beaks. They use strong fused teeth to scrape algae and tiny foods from reef surfaces, helping keep coral reefs cleaner and full of life.

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Penguins are flightless birds that are excellent swimmers. They have flipper-like wings, waterproof feathers, webbed feet, and strong bodies built for ocean life. Most penguins live in the Southern Hemisphere.

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Pipefish are long, slender relatives of seahorses and seadragons. Their bodies resemble pencils or pieces of seagrass, and their narrow tube-shaped snouts suck in tiny prey. The most astonishing part of pipefish family life is that males carry the developing eggs—sometimes inside a pouch and sometimes attached beneath the body—until the young are ready to hatch.

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Porcupinefish are broad-bodied ocean fish covered with spines. When threatened, many can puff up by taking in water, making the spines stand out and turning the fish into a round, prickly ball that is hard to swallow.

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Porpoises are seven living species of small toothed whales in the family Phocoenidae. They are close relatives of dolphins but form a different family. Most have compact bodies, rounded heads without a long beak, and small spade-shaped teeth. From shy harbor porpoises to speedy Dall’s porpoises and critically endangered vaquitas, each species has its own range and conservation story.

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The Portuguese man o' war looks like a jellyfish, but it is actually a siphonophore, a floating colony of specialized parts working together. It has a blue or purple gas-filled float and long stinging tentacles that drift below.

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“Prawn” is a common name rather than one perfectly fixed scientific group. In many biological descriptions it refers especially to shrimp-shaped decapod crustaceans in the suborder Dendrobranchiata, which have tree-like branching gills and usually release their eggs into the water. Everyday names vary by country, so some animals called prawns belong to other groups and may be called shrimp elsewhere.

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Pufferfish are unusual fish famous for puffing their bodies into round balloon shapes when threatened. Many have tough skin, small fins, strong beak-like teeth, and powerful toxins that help protect them from predators.

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Puffins are small seabirds with black-and-white feathers, orange feet, and bright colorful beaks during breeding season. They nest in colonies on cliffs and islands and dive underwater to catch fish.

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The razorbill, Alca torda, is a black-and-white seabird in the auk family. Its thick, flattened bill and upright stance may remind you of a penguin, but razorbills can fly. They breed on rocky North Atlantic coasts and spend most of the rest of the year at sea, where their wings become powerful underwater paddles for chasing fish.

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Reef shark is a common name for several shark species that live around coral reefs, including blacktip reef sharks, whitetip reef sharks, grey reef sharks, and Caribbean reef sharks. These sharks help reef food webs stay balanced and need healthy reefs to survive.

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The ringed seal, Pusa hispida, is a small true seal adapted to icy northern waters. Pale rings and spots pattern its darker back, while strong front claws keep breathing holes open in sea ice. Most ringed seals live around the Arctic Ocean, but distinct subspecies also inhabit the Baltic Sea and the freshwater lakes Ladoga and Saimaa. Snow, ice, and access to water shape nearly every part of their lives.

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Rockhopper penguins are small crested penguins with bright yellow eyebrow feathers, red eyes, and big attitudes. They live in noisy colonies on rocky islands and hop over rocks instead of waddling smoothly like some penguins.

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Sailfish are fast open-ocean fish named for the huge sail-like dorsal fin on their backs. They have long bills, sleek bodies, blue stripes, and quick hunting skills that help them chase small fish and squid near the ocean surface.

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Salps are transparent, barrel-shaped ocean animals in the tunicate group. They may resemble jellyfish, but they are chordates and are more closely related to animals with backbones than to true jellyfish. A salp draws water through its body to collect tiny food and then squirts the water out, so one simple system provides both dinner and jet-powered travel.

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Sand dollars are flat ocean animals related to sea urchins and sea stars. Living sand dollars are covered with tiny spines and move slowly through sandy seafloors, while the pale “sand dollars” found on beaches are usually their dried skeletons.

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Sawfishes are huge, shark-shaped rays with long, flat snouts edged by tooth-like spikes. The five living species belong to the family Pristidae and once occupied warm coastal waters and rivers across much of the world. Their sensitive saws help them locate and capture prey, but they also tangle easily in fishing nets. All five species are now Critically Endangered.

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Sawsharks are slender sharks with long, saw-like snouts, a pair of dangling sensory barbels, and rows of sharp rostral teeth. Ten living species in the family Pristiophoridae inhabit parts of the Atlantic, Indian, and Pacific oceans, usually near the seafloor. They are far smaller than sawfishes and can be identified by gill slits on the sides of the head.

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Scallops are bivalve mollusks that make fan-shaped shells. Unlike many other bivalves, some scallops can swim by clapping their shells together and pushing water out in quick jets.

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Sea anemones are soft ocean animals that look like colorful underwater flowers. They belong to the cnidarian group and use tentacles with tiny stinging structures to catch food, so they should be watched gently and not touched.

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Sea angels are tiny swimming sea slugs in the gastropod group Gymnosomata. Their transparent bodies and two flapping parapodia can make them look like angels with wings, but they are skilled open-ocean predators. Many hunt shelled pteropods called sea butterflies, sometimes pulling the prey from its shell with hidden grasping structures and hooks.

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Sea butterflies are tiny pelagic snails commonly grouped as shelled pteropods, especially the Thecosomata. They flutter through seawater using a muscular foot divided into two wing-like parapodia. Many build thin, transparent shells and collect microscopic food with mucus webs, making them important links between plankton and larger animals such as fish and whales.

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Sea cucumbers are soft, tube-shaped marine animals that crawl along the sea floor. They are echinoderms, related to sea stars and sea urchins, and many help recycle nutrients by eating tiny food bits mixed with sand or mud.

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Seadragons are delicate marine fishes related to seahorses and pipefishes. The three recognized species—the leafy, common or weedy, and ruby seadragons—live only along southern Australia. Their long snouts, slender bodies, and camouflage make them look like drifting seaweed, while nearly transparent fins provide the real swimming power.

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Sea hares are soft marine mollusks that look like chunky sea slugs with rabbit-ear-like tentacles. They often eat seaweed, crawl along shallow ocean bottoms, and some can release purple or reddish ink when bothered.

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Sea kraits are venomous sea snakes that split life between ocean and land. They hunt in coral reefs and coastal waters, but unlike fully ocean-living sea snakes, sea kraits return to land to rest, digest food, shed skin, mate, and lay eggs.

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Sea lions are lively marine mammals with strong front flippers, small visible ear flaps, loud barks, and playful swimming skills. They are related to seals and walruses, but they move on land differently from true seals.

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Sea otters are playful-looking marine mammals that live along northern Pacific coasts. They float on their backs, use rocks as tools, have super dense fur, and help keep kelp forests healthy by eating sea urchins.

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Sea slug is an informal name for many soft-bodied marine gastropods, including nudibranchs, sea hares, and sap-sucking sacoglossans. They are relatives of snails, but most adults have reduced or missing shells. Sea slugs inhabit oceans worldwide and use camouflage, warning colors, chemicals, mucus, or even defenses borrowed from their food to survive.

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Sea snakes are marine reptiles that live in warm ocean waters. They are related to cobras, have venom, breathe air at the surface, and many have flattened paddle-like tails that help them swim through reefs, lagoons, and coastal seas.

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Sea sponges are simple marine animals that live attached to rocks, reefs, shells, or the sea floor. They have many tiny pores, no brain like ours, and a clever filter-feeding system that moves water through the body to catch tiny food particles.

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Sea turtles are ocean reptiles with shells, flippers, lungs, and long life cycles. They live in the world’s oceans and come onto beaches to lay eggs in sandy nests.

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Sea urchins are round, spiky marine animals that live on the ocean floor. They are echinoderms, which means they are related to sea stars and sand dollars, and they use tiny tube feet, spines, and a special mouth structure to move and eat.

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Seagulls are usually called gulls by scientists. They are clever, noisy seabirds with webbed feet, strong wings, loud calls, and flexible diets that help them live near oceans, lakes, rivers, cities, and harbors.

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Seahorses are small ocean fish with horse-shaped heads, curled tails, bony body rings, and tiny mouths. They live in shallow coastal waters such as seagrass beds, coral reefs, mangroves, and estuaries.

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Seals are marine mammals with smooth bodies, flippers, whiskers, and thick blubber. They spend lots of time in water, but they also come onto land or ice to rest, warm up, and raise their pups.

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Sharks are cartilaginous fishes with five to seven gill slits on each side, tooth-like scales, and fins that are not fused to the head. More than 500 living species range from a hand-sized lanternshark to the enormous plankton-eating whale shark. They occupy oceans worldwide, and a few enter or live in rivers, with diets and lifestyles far more varied than movie monsters suggest.

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Shrimp are small crustaceans that live in oceans, rivers, lakes, estuaries, and muddy or sandy bottoms depending on species. They have long antennae, many legs, hard outer shells, gills, and a quick backward-swimming escape move.

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Skates are flattened cartilaginous fishes closely related to sharks and other rays. Most live on or near the seafloor, where broad pectoral fins form a diamond-shaped disc around the head and body. Unlike stingrays, true skates lack a venomous tail stinger and reproduce by laying tough egg cases popularly called mermaid’s purses.

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The southern elephant seal is the largest seal and one of Earth’s most extreme diving mammals. It breeds and molts on subantarctic and southern coasts but spends most of its life roaming the cold Southern Ocean for fish and squid. An adult male can weigh several times as much as a female and develops the inflatable trunk-like nose that gives elephant seals their name.

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The sperm whale is the largest toothed whale and the biggest living predator with teeth. Its enormous square head contains sound-producing structures that create powerful echolocation clicks for exploring the dark ocean. Sperm whales live in deep seas around the world, dive far below sunlight for squid and fish, and maintain rich social lives built around families, vocal patterns, and long-distance journeys.

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Squid are fast ocean mollusks in the cephalopod group. They have soft bodies, big eyes, eight arms, two longer tentacles, a beak, and a siphon that helps them jet through the water like tiny sea rockets.

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Starfish are better called sea stars because they are not fish. They are marine invertebrates related to sea urchins and sand dollars, with arms, tube feet, spiny skin, and amazing ways to move, eat, and regrow body parts.

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Stingrays are flat ocean fish related to sharks. They glide over sandy seafloors with wing-like fins, breathe through gills, and many have a sharp tail barb used for defense when they feel threatened.

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Stonefish are thick, bumpy fish that rest on the seafloor and blend in with rocks, coral rubble, or sand. They are famous for powerful venomous spines, so people should never touch or step on them and should use caution in stonefish areas.

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Swordfish are large ocean fish named for the long, flat sword-like bill that sticks out from the front of the head. They are powerful swimmers found in warm and temperate oceans, where they hunt fish and squid.

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Terns are graceful seabirds with narrow wings, forked tails, and sharp bills. Many terns fly over oceans, lakes, rivers, and coasts, then plunge toward the water to catch small fish and other prey.

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Tiger sharks are large ocean sharks named for the dark stripes seen most clearly on young sharks. They are powerful predators and scavengers with sharp serrated teeth, strong senses, and a very wide menu, but people should always admire wild sharks from a safe distance.

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Triggerfish are strong reef fish with deep bodies, small mouths, tough scales, and clever locking spines. They live around reefs and rocky areas, where many feed on hard-shelled animals, sea urchins, crustaceans, and other reef foods.

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Turtles have traveled Earth for more than 200 million years. Their order includes sea turtles, freshwater turtles, terrapins, box turtles, and tortoises. From a tiny bog turtle to a giant leatherback, every species carries a remarkable shell that is built into its skeleton.

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Vampire squid are deep-sea cephalopods with dark bodies, glowing arm tips, big eyes, and webbing between the arms that looks like a little cape. Despite the spooky name, they do not drink blood and mostly feed on drifting ocean particles called marine snow.

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Walruses are huge Arctic marine mammals with long tusks, thick blubber, wrinkly skin, stiff whiskers, and flippers. They spend time in cold seas and haul out on ice or beaches to rest.

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The Weddell Seal, Leptonychotes weddellii, is a large true seal that lives around Antarctica, especially beside stable coastal fast ice. It is the only living species in its genus and is famous for maintaining breathing holes with its teeth, making eerie underwater calls, and diving beneath sea ice for fish and other prey. Weddell Seals breed farther south than any other mammal, but they still need open cracks or holes because they breathe air. Their global IUCN category is Least Concern, while climate-driven changes to sea ice and food webs remain important long-term concerns.

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Weedy sea dragons are delicate fish from southern Australian waters. They look like drifting seaweed, with long snouts, leafy-looking body parts, bony plates, and gentle slow swimming that helps them hide among kelp and seagrass.

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Whale is a broad common name for many cetacean mammals, ranging from the enormous blue whale to much smaller toothed species. Cetaceans are divided into baleen whales, or mysticetes, and toothed whales, or odontocetes; dolphins and porpoises are scientifically part of the toothed-whale branch even though everyday speech often lists them separately. Whales breathe air, give birth to live young, nurse calves with milk, and use sound in remarkable ways. Species differ enormously in size, diet, migration, social life, diving ability, and conservation status, so no single fact fits every whale.

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Whale sharks are gentle ocean giants and the largest fish in the world. Even though their name includes “whale,” they are sharks, not whales. They swim with wide mouths to filter tiny food from seawater.

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Wrasses are a large group of colorful marine fish often found on coral reefs and rocky reefs. Many wrasses have thick lips, strong front teeth, bright patterns, and busy reef lives full of hunting, cleaning, hiding, and quick swimming.

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Yellow-eyed penguins, also called hoiho, are rare penguins from New Zealand. They have pale yellow eyes, a yellow band of feathers around the head, shy nesting habits, and a conservation story that needs careful protection.

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