The immortal jellyfish is so-called because it can revert to a previous stage in its life cycle due to stress or injury. However, this isn't immortality as we typically think of it: the jelly turns back into a stationary polyp that spawns several genetically identical medusae.

The hairy frogfish doesn't pursue prey. Instead, it wobbles along the sea floor, finds a hiding spot, and uses a worm-like appendage on its head to lure in a victim. Its body is covered in spines which resemble strands of hair — camouflaging it amongst seaweed, assisted by colour-changing abilities.

Marine hatchetfish are creatures of the deep. They have rows of light-producing organs along their bellies which shine a pale blue — matching the light from above and making the hatchetfish invisible to predators below. This fish's name comes from its body shape, which resembles the head of a hatchet.

Skeleton shrimp are skeletally thin and often have ghostly transparent bodies. They grasp algae with their spindly rear legs, while their front legs form large "claws" used for grooming, defence, and capturing prey. Luckily, they only grow to a couple of centimetres (~1 inch) long.

A sea pen may look like an underwater quill, but it's actually a colony of individual polyps — one polyp becomes the stalk of the sea pen and the bulb that attaches it to the sea floor, while the rest form feathery branches. Some sea pens have only a few polyps, while others have as many as 35,000.

A remora uses the sucking disk on top of its head to attach itself to larger marine animals like sharks, rays, and sea turtles — where it can stay for 3 months. The host provides the remora with protection, food, and a fast flow of water over its gills, which the remora needs in order to survive.