Blue whale

 

The blue whale (Balaenoptera musculus) is the largest known animal on Earth, reaching lengths of up to 30 meters (98 feet) and weights of up to 200 metric tons.

They have a long, streamlined body with a bluish-gray coloration that appears blue underwater. 

Their underbellies are often lighter and can appear yellowish due to the presence of microorganisms.

They have small dorsal fins located near their tails and long, slender flippers. Their tails, or flukes, are broad and triangular.

Blue whales are found in all the world's oceans except the Arctic. They prefer deep oceanic waters.

They are migratory animals, traveling long distances between feeding grounds in polar waters and breeding grounds in tropical or subtropical waters.

Their primary diet consists of small shrimp-like animals called krill. 

An adult blue whale can consume up to 4 tons of krill per day during the feeding season.

They are baleen whales, meaning they have baleen plates instead of teeth. 

They take in large mouthfuls of water and krill and then push the water out through their baleen plates, which trap the krill.

Female blue whales give birth to a single calf every two to three years after a gestation period of about 11-12 months. 

Calves are born in warmer waters and can be up to 25 feet (7.6 meters) long at birth.

Blue whales can live up to 80-90 years, though some individuals have been estimated to live over 100 years.

Blue whales are classified as endangered by the International Union for Conservation of Nature (IUCN). 

Their populations were severely reduced due to commercial whaling in the 20th century.

They are now protected under international laws, and their populations are slowly recovering, though they still face threats from ship strikes, entanglement in fishing gear, and the impacts of climate change.

Blue whales are known for their loud, low-frequency calls, which can be heard over hundreds of miles underwater. 

These calls are used for communication and possibly navigation.

The heart of a blue whale can weigh as much as a small car, and their aorta is large enough for a human child to crawl through.