Here are the most dangerous creatures in the sea life.

Crocodile

A crocodile is any species belonging to the family Crocodylidae (sometimes classified instead as the subfamily Crocodylinae). The term can also be used more loosely to include all members of the order Crocodilia: i.e. the true crocodiles, the alligators and caimans (family Alligatoridae) and the gharials (family Gavialidae), or even the Crocodylomorpha which includes prehistoric crocodile relatives and ancestors.

Member species of the family Crocodylidae are large aquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. Crocodiles tend to congregate in freshwater habitats like rivers, lakes, wetlands and sometimes in brackish water. They feed mostly on vertebrates like fish, reptiles, and mammals, sometimes on invertebrates like mollusks and crustaceans, depending on species. They are an ancient lineage, and are believed to have changed little since the time of the dinosaurs. They are believed to be 200 million years old whereas dinosaurs became extinct 65 million years ago; crocodiles survived great extinction events.

Octopus

The octopus is a cephalopod mollusc in the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms. Most octopuses have no internal or external skeleton, allowing them to squeeze through tight places. Octopuses are highly intelligent, probably the most intelligent of all invertebrates.

The octopus inhabits many diverse regions of the ocean, especially coral reefs. For defense against predators, they hide, flee quickly, expel ink, or use color-changing camouflage. An octopus trails its eight arms behind it as it swims. All octopuses are venomous, but only the small blue-ringed octopuses are known to be deadly to humans.

In the larger sense, there are around 300 recognized octopus species, which is over one-third of the total number of known cephalopod species. The term octopus may also be used to refer only to those creatures in the genus Octopus.

Sea lion

Sea lions are any of seven species in seven genera of modern pinnipeds including one extinct species (the Japanese sea lion). Sea lions are characterized by the presence of external ear pinnae (ear-flaps), long front flippers, the ability to walk on all four flippers on land, and the lack of dense underfur. Their range extends from the subarctic to tropical waters of the global ocean in both the northern and southern hemispheres with the notable exception of the Atlantic Ocean.

Sailfish

Sailfish are two species of fish in the genus Istiophorus, living in warmer sections of all the oceans of the world. They are blue to grey in color and have a characteristic erectile dorsal fin known as a sail, which often stretches the entire length of the back. Another notable characteristic is the elongated bill, resembling that of the swordfish and other marlins. They are therefore described as billfish in sport fishing circles.

Both species of sailfish grow quickly, reaching 1.2-1.5 m (4-5 ft) in length in a single year, and feed on the surface or at mid-depths on smaller pelagic forage fish and squid. Individuals have been clocked at speeds of up to 110 km/h (70 mph), which is the highest speed reliably reported in a fish. Generally, sailfish do not grow to more than 3 m (10 ft) in length and rarely weigh over 90 kg (200 lb).

The sail is normally kept folded down and to the side when swimming, but it may be raised when the sailfish feels threatened or excited, making the fish appear much larger than it actually is. This tactic has also been observed during feeding, when a group of sailfish use their sails to “herd” a school of fish or squid.

Sailfish are highly prized game fish and are known for their incredible jumps. The sailfish can also rapidly turn its body light blue with stripes when excited, confusing its prey and making capture easier, while signalling its intentions to fellow sailfish.

Swordfish

Swordfish (Xiphias gladius; from Greek ξίφος: sword, and Latin gladius: sword), also known as Broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood. These fish can live close to shore. They reach a maximum size of 14 ft 9 in (455 cm) and 1,400 lb (650 kg). The International Game Fish Association’s all-tackle angling record for a swordfish was a 1,182 lb (536.15 kg) specimen taken off Chile in 1953.

They are the sole member of their family Xiphiidae.

Barracuda

The barracuda is a ray-finned fish known for its large size and fearsome appearance. Its body is long, fairly compressed, and covered with small, smooth scales. Some species could reach up to 1.8m in length and 30 centimeters (11.8 in) in width. The barracuda is a salt water fish of the genus Sphyraena, the only genus in the family Sphyraenidae, and is found in tropical and subtropical oceans worldwide.

Moray Eel

Moray eels are cosmopolitan eels of the family Muraenidae. The approximately 200 species in 15 genera are almost exclusively marine, but several species are regularly seen in brackish water and a few, for example the freshwater moray (Gymnothorax polyuranodon) can sometimes be found in freshwater. With a maximum length of 11.5 centimetres (4.5 in), the smallest moray is likely the Snyder’s moray (Anarchias leucurus),[3] while the longest species, the slender giant moray (Strophidon sathete) reaches up to 4 metres (13 ft). The largest in terms of total mass is the giant moray (Gymnothorax javanicus), which reaches almost 3 metres (9.8 ft) and can weigh over 36 kilograms (79 lb).

Shark

Sharks (superorder Selachimorpha) are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago, before the time of the dinosaurs.

Since that time, sharks have diversified into 440 species, ranging in size from the small dwarf lanternshark, Etmopterus perryi, a deep sea species of only 17 centimetres (6.7 in) in length, to the whale shark, Rhincodon typus, the largest fish, which reaches approximately 12 metres (39 ft 4 in) and which feeds only on plankton, squid, and small fish by filter feeding. Sharks are found in all seas and are common down to depths of 2,000 metres (6,562 ft). They generally do not live in freshwater, with a few exceptions such as the bull shark and the river shark which can live both in seawater and freshwater. They breathe through five to seven gill slits. Sharks have a covering of dermal denticles that protect their skin from damage and also have parasites that improve their fluid dynamics so the shark can move faster. They have several sets of replaceable teeth.

Well-known species such as the great white shark, tiger shark, and the hammerhead are apex predators, at the top of the underwater food chain. Their extraordinary skills as predators fascinate and frighten humans, even as their survival is under serious threat from fishing and other human activities.