Jellyfish

Jellyfish have many unique adaptations. One such adaptation are the stinging cells in their long tentacles, which protect their soft tissue, keep them warm in the cold waters of the ocean and aid them in catching their prey by immobilizing them and moving it to their mouths. Another adaptation of the jellyfish is that it is made of 90 percent water which allows it to float easily. Jellyfish can live in areas with high salinity and low oxygen waters and thus are able to bloom easily because they can thrive on plankton without having to compete with other species. They do not require any sort of respiratory system since they have very thin skin which absorb gases easily and do not even have a complex digestive tract and have instead a cavity with a gastrodermal lining which helps it absorb nutrients.

Lionfish - Sharp and Deadly

Notice the spike-like dorsal fins of the lionfish. When viewed from afar, those fins make the lionfish look like a lion. These fins are also venomous. The dorsal fins of a lionfish are known to cause nausea and breathing difficulties to humans who get stung, but the same cannot be said for other fishes. Its red and white zebra-like stripes help it camouflage, especially when it is amongst coloured coral. This means that the lionfish can use its stealth to ambush prey, strike out with lightning speed, and use its venom to paralyse its prey before devouring it.

Moray eel - Special swimmers.

Moray eels have no pelvic fins, which lets them have the ability to tie their bodies in knots and use this to gain leverage when tearing food. This also means that moray eels use anguilliform swimming, which is a form of swimming in which flexible fish swim by flexing the whole body into lateral waves. This is used to great effect when the eels dart forward out of a crevice to seize prey (invertebrates and fishes). They can swim nearly as well backward, which is handy for entering into the shelter of a crevice or hole to avoid predators.

Starfish - Regeneration.

Starfish have many unique adaptations, of which one of them is regeneration. If a starfish loses its arm, organ or most of their body, they have the ability to grow it back as long as part of the central ring is not damaged. With this adaptation, a starfish cannot bleed to death, get an infection or become permanently crippled if a predator attacks. One starfish may also become two if part of the central ring is separated from the main body. Some starfish even decide to intentionally reproduce like this in the event that the population is dwindling.

Leafy Sea Dragons - Elusive and Undetectable.

When we were looking at the sea dragons during the trip, most of us could spot the weedy sea dragon quite easily, due to its unique twig/ weed-like structure. However, we had some trouble spotting its more elusive cousin, the leafy sea dragon. After a long search, we finally spotted it hiding among the seaweed. 

The leafy sea dragon has structural adaptations to help it survive in the sea. It has leafy protrusions from its head, body and tail which enables them to blend with the plants in their environment as the leafy sea dragons look like, well, leaves. 

This means that when a predator of the leafy sea dragon swims past, it will not notice the leafy sea dragon as not only is the the structure of the leafy sea dragon similar to seaweed, the brown and yellow colors of the sea dragon are also alike to the colour of the seaweed, therefore making it very hard to spot.

A picture of a leafy sea dragon. Notice the leaf like protrusions all over its body that aids it in camouflage.

Mudskippers - Special fins, unique gills.

The mudskipper has a special type of gills, which are specially designed to trap water in the mudskipper's gill chamber, therefore keeping the gills moist and allowing them to function. The mudskipper's neck also houses blood rich membranes and the water is also used to moisten the mudskipper's skin, thereby allowing it to absorb air and stay alive for a long period of time. The mudskipper also has a highly modified type of fins that allow it to "walk" on land, as well as flip its body to "skip" across mud or even water.

Source(s):
http://www.newyorktails.com/mudskippers.htm
http://www.aquariumofpacific.org/onlinelearningcenter/species/mudskipper