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.

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.