1. Blue Whale
The blue whale (Balaenoptera musculus) is a marine mammal and a baleen whale. Reaching a maximum confirmed length of 29.9 meters (98 feet) and weighing up to 199 metric tons (196 long tons. 219 short tons), it's the largest animal known to have ever existed. The blue whale's long and slender body can be of various shades of greyish-blue on the back and somewhat lighter underneath.
Four subspecies are recognized: B. m. musculus in the North Atlantic and North Pacific, B. m. intermedia in the Southern Ocean, B. m. brevicauda (the pygmy blue whale) in the Indian Ocean and South Pacific Ocean, and B. m. indica in the Northern Indian Ocean. There's also a population in the waters off Chile that may constitute a fifth subspecies.
In general, blue whale populations migrate between their summer feeding areas near the poles and their winter breeding grounds near the tropics. There's also evidence of year-round residencies and partial or age- and sex-based migration. Blue whales are filter feeders. Their diet consists almost exclusively of krill. They're generally solitary or gather in small groups, with no well-defined social structure beyond mother-calf bonds. The fundamental frequency for blue whale vocalizations ranges from 8 to 25 Hz, and vocal production may vary by region, season, behavior, and time of day. Orcas are their only natural predators.
The blue whale was once abundant in nearly all of Earth's oceans until the end of the 19th century. It was hunted almost to extinction by whalers until the International Whaling Commission banned all blue whale hunting in 1966. The International Union for Conservation of Nature listed blue whales as endangered as of 2018. They continue to face numerous man-made threats such as ship strikes, pollution, ocean noise, and climate change.
2. Red-Eyed Tree Frog
3. West Indian Manatee
4. Asian Otter
5. Axolotl
The axolotl, scientifically known as Ambystoma mexicanum, is a neotenic salamander closely related to the tiger salamander. Often referred to as the "Mexican walking fish," the axolotl is not actually a fish but an amphibian.
It is native to the remnants of Lake Xochimilco in Mexico and was formerly found in Lake Chalco before it was drained. Wild axolotls are typically brown or black in color, while captive-bred specimens can exhibit a variety of hues and may even fluoresce under blue light due to genetic modification.
6. Roe Deer
7. Ocean Sunfish
8. Porcupine Fish
9. Hedgehog
A hedgehog is any of the spiny mammals of the subfamily Erinaceinae, in the eulipotyphlan family Erinaceidae. They are native to parts of Europe, Asia, and Africa, and have also been introduced into New Zealand. Hedgehogs are nocturnal and known for their defensive behavior of rolling into a tight ball when threatened.
10. Dolphin
A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (oceanic dolphins), Platanistidae (Indian river dolphins), Iniidae (New World river dolphins), Pontoporiidae (brackish water dolphins), and the extinct Lipotidae (baiji or Chinese river dolphin). There are currently 40 extant species recognized as dolphins.
Dolphins range in size from the 1.7-meter-long (5 ft 7 in), 50-kilogram (110-pound) Maui's dolphin to the orca, which can reach up to 9.5 meters (31 ft 2 in) in length and weigh as much as 10 tonnes (11 short tons). Some species exhibit sexual dimorphism, with males generally larger than females. Dolphins have streamlined bodies and two limbs modified into flippers. While not as flexible as seals, some dolphins can briefly reach speeds of up to 29 kilometers (18 miles) per hour or leap up to 9.1 meters (30 feet) in the air.
Dolphins use their conical teeth to catch fast-moving prey. They have highly developed hearing adapted for both air and water, and some species can survive even if blind due to their echolocation abilities. Many dolphins are adapted for deep diving and possess a thick layer of blubber under their skin for insulation in cold waters.
Dolphins are found worldwide. While most species inhabit warm tropical and subtropical waters, some, such as the right whale dolphin, are found in colder environments. Dolphins primarily feed on fish and squid, though species like the orca also hunt marine mammals. Males typically mate with multiple females each year, whereas females usually reproduce every two to three years. Calves are generally born in spring or summer, and mothers are solely responsible for their upbringing. In some species, mothers fast and nurse their young for extended periods.
Dolphins communicate using a variety of vocalizations, including clicks and whistles. They are sometimes hunted in places like Japan in practices such as dolphin drive hunting. Additional threats include bycatch, habitat loss, and marine pollution. Dolphins have been depicted in cultures around the world and are featured in films such as the Free Willy series. Bottlenose dolphins are the most commonly kept species in captivity, and as of 2025, there are approximately 60 orcas held in marine parks.
