At 98 ft. (30 metres) and 200 tons (180 metric tons) in weight, the Blue Whale is the largest known animal to have ever existed. During the summer feeding season a Blue Whale may eat up to 40 million krill a day. (Left: Blue whale from above; Right: Blue whale skull.)
These mysterious deep sea dwellers are the largest invertebrates on Earth. The biggest ever one found measured 59 feet (18 meters) in length and weighed nearly a ton (900 kilograms).
A type of crustacean distantly related to the shrimp and crabs, the Giant Isopod has a maximum weight and length of approximately 3.7 lbs. (1.7 kilograms) and 30 inches (76 centimeters) respectively.
Also called the finback whale, razorback, or common rorqual, this marine mammal is the second largest animal after the blue whale, growing to 89.5 ft. (27.3 meters) long and weighing nearly 82 short tons (74 tonnes).
Giant Pacific Octopus
This cephalopod grows bigger and lives longer than any other octopus species. The size record is held by a specimen that was 30 feet (9.1 meters) across and weighed more than 600 pounds (272 kilograms).
Giant Oceanic Manta Ray
Oceanic mantas are the largest type of ray in the world. They can grow to a width of 30 ft. (9 meters) and can live for 20 years.
Southern Elephant Seal
Southern elephants are the largest of all seals. Males can be over 20 feet (6 meters) long and weigh up to 8,800 pounds (4,000 kilograms). Interestingly, they aren't called elephant seals because of their massive size. The name is actually inspired by their trunk-like snouts.
Mature male sperm whales may reach 67 ft. (20.5 metres), with the head representing up to one-third of its length. The sperm whale is capable of diving to depths of 7,380 ft in search of squid, its favorite prey.
The giant oarfish starts out small but grows up to be the longest bony fish alive, achieving lengths of up 11 m (36 ft) in length. (Top: a baby oarfish; Bottom; United States servicemen hold a 23-foot (7.0 m) giant oarfish, found washed up on the shore near San Diego, California in September 1996)
Giant Tube Worm
These worms can reach a length of 7 ft 10 in (2.4 meters) and their tubular bodies have a diameter of 1.6 in. (4 cm). They live up to several miles deep, on the floor of the Pacific Ocean near black smokers, and it can tolerate extremely high hydrogen sulfide levels.
Caribbean Barrel Sponge
This impressive sponge may live for 100 years and grow to over 6 feet tall and/or 6 feet in diameter.
Lions Mane Jellyfish
Also known as 'hair jelly,' the lion's mane is the largest known species of jellyfish. The largest recorded specimen, found washed up on the shore of Massachusetts Bay in 1870, had a bell (body) with a diameter of 7 ft 6 in (2.3 metres) and tentacles 120 ft (37 m) long. (Image: A life-size model of a Lion's Mane Jellyfish at the Smithsonian Museum of Natural History in Washington, D.C., USA)
The whale shark is a slow-moving, filter feeding shark and the largest known extant fish species. The largest confirmed specimen had a length of 41.50 ft. (12.65 m) and a weight of more than 47,000 lb (21.5 metric tons).
Giant Sea Star
This species of sea star lives along the western coast of North America from Southern California to British Columbia. It can grow as large as 24 in (61 cm) in diameter.
Japanese Spider Crab
The Japanese spider crab has the greatest leg span of any arthropod, reaching 12 feet (3.8 meters) from claw to claw. The body may grow to a size of 40 cm or 16 in (carapace width) and the whole crab can weigh up to 42 lbs (19 kilograms).
Often mistaken for a jellyfish, the Portuguese man-of-war is a siphonophore, an animal made up of a colony of organisms working together. Although its body is generally only about 12 in (30 cm) long, and 5 in (12.7 cm) wide, its tentacles can extend up to 165 ft (50 m).
Great White Shark
Known mainly for its size and ferocity, a mature great white shark grow can up to 21 ft. (6.4 m) in length and 7,328 lb (3,324 kg) in weight).Its lifespan is estimated to be as long as 70 years or more, and it can accelerate to over 35 mph (56 km/h).
This bottom-dwelling behemoth is the largest mollusks on Earth, capable of reaching 4 feet (1.2 meters) in length and weighing more than 500 pounds (227 kg). Once it fastens itself to a spot on a reef, it stays there for the rest of its life.
Want to see more incredible ocean creatures? Check out: 18 Neon Nudibranchs That Are The Trippiest Things In The Sea