Nautilus, like octopuses and squids, are molluscs. They live in tropical waters stretching from the Andaman Sea east to Fiji and from southern Japan to the Great Barrier Reef. During the day, nautiluses live at a depth of about 600 m, but at night they move to shallow water to eat crabs and juvenile fish. Photo: Calacademy.

There are many species of squid that live in the deep sea such as giant squid, vampire squid and bigfin squid. According to National Geographic , vampire squid can live comfortably at a depth of 3,000 m in the ocean. Vampire squids feed by sucking things floating in deep water such as eggs, larvae, and the bodies of other small marine animals. Photo: Pinterest .

The fangtooth fish is a ferocious-looking fish, with a body length of about 17 cm. They live at depths of nearly 5,000 m in tropical and temperate seas around the world. Fangtooth fish do not lie in wait for prey but actively search for food, trapping prey with their wide mouth and long teeth. Photo: Wikipedia.

Cookiecutter sharks have quite scary-looking teeth. Their body is long and cylindrical like a cigar. An adult fish weighs about 4.5 kg and is 0.6 meters long. They like to live in warm waters near the equator at depths of more than 300 m. Photo: Oceana.

Frill sharks are often called “living fossils” because their appearance has changed very little in the past 80 million years. We rarely encounter this fish because it lives at a depth of 1,200 m. The frilled shark has an eel-like body and possesses 25 rows of teeth with a total of 300 teeth. Adult individuals can be from 1.5 to 1.8 m long. Photo: Flickr.

Japanese spider crabs have the largest leg length among crustaceans. The leg extension of an adult individual is up to 4 m. They live on the southern coast of Honshu island, from Tokyo Bay to Kagoshima and some areas beyond. Giant crabs weighing 15 to 20 kg usually live at a depth of about 150 m to 300 m below the seabed. Photo: Jeff Rotman.

Giant tube worms live in hydrothermal vents at the bottom of the Pacific Ocean. Even in dark and harsh environments, tube worms can grow up to 2.4 m tall. Giant tubeworms are the fastest growing invertebrates, growing up to 33 cm each year. Photo: Wikipedia.

Oarfish are often referred to as snakes or sea dragons. They are the longest bony fish in the world, with a total length of about 8 m. This animal lives at a depth of 1,000 meters under the sea. Most of what we know about them comes from specimens that wash ashore. Photo: Wikimedia.

Squat lobsters are scavengers capable of living at a depth of 1,400 m below the seabed. They are often blind, have soft bodies, have lots of hair around them, and do not have a shell on their back. Photo: Flickr.