Warty frogfish. It is one of the weirdest looking creatures seen underwater.

Frogfish can open its mouth as wide as its body and can swallow prey as big as the frogfish itself.

This frogfish doesn't look happy posing for the photo.

Warty frogfish - or clown frogfish, this one is still a juvenile. Frogfishes can change their colours and patterns in a few weeks depending on their current surroundings.

Frogfish can use their fins as "legs".

Coral reefs are riddled with worms of all shapes, sizes ranging from a millimeter or so up to more than two meters.

Turbellarian penis fencing. Yes, you read that right. Some of the larger aquatic flatworm species mate by penis fencing: a duel in which each tries to impregnate the other. Each flatworm has two penises, the white spikes on the undersides of their heads.

The winner strikes its penis straight through the other one's body. The loser of the fencing contest adopts the female role of developing the eggs.

We may have a winner...

Hancock's flatworm.

Popular photo targets for scuba divers - for obvious reasons.

Nudibranchs have both male and female sex organs at the same time. Every mature individual of the same species is a potential partner, which is handy as nudibranchs don't move very fast and can't travel long distances.

Nudibranch - Chromodoris hintuanensis laying a yellow egg ribbon. The egg masses vary in shape, size and colour depending on species. The process can take hours.

A shrimp living in a sea squirt. Shrimps take residence in various hosts.

Crinoid shrimps match their colors based on the crinoid they live on.

Mushroom Coral Shrimp

Cuttlefish have W-shaped eyes. They can not see colors, but yet they are able to match their skin color and texture according to their surroundings even in total darkness.

Cuttlefish can change the color, patterns and even the texture of their skin to camouflage from predators or dazzle their prey.

A Flamboyant cuttlefish showing off its colors. Flamboyant Cuttlefish is somewhat unique among cuttlefish and its relatives: it is one of only three known poisonous cephalopods and thus not fit for human consumption.

A tiny squid.

Pygmy Squid

Octopuses have two eyes, eight arms and three hearts.

Octopuses have various strategies for defending themselves against predators, including the expulsion of ink, the use of camouflage and startling color displays, their ability to jet quickly through the water, and their ability to hide.

Octopus has no internal or external skeleton. They can squeeze themselves through holes much smaller than their bodies.

What would a collection of critters be without every certified scuba diver's favourite: Clownfish aka Nemo. Clownfish live with sea anemones: the anemone protects the clownfish from predators with its stinging tentacles, as well as provides food through the scraps left from the anemone's meals. In return, the clownfish defends the anemone from its predators and parasites.

Clownfish can change genders. They are born male but turn into females as they mature or if the female of the pair dies. Sorry, the movie Finding Nemo couldn't have happened: Nemo's father would have turned into his mother...

Anemonefish are unaffected by the stinging tentacles of the host anemone.

Juvenile barracudas congregate and form large schools. They often swim around divers in circles.