Jellyfish

Researchers have known that an animal swimming parallel to a solid surface receive a subsequent boost in performance, thus allowing them to utilise less energy when moving around. 
 
Studies have quantified this into a 25 percent increase in speed and a 45 percent increase in thrust when swimming near a solid surface. 

However, the jellyfish does not swim near the seafloor or seawalls. How does it get named the "world's most efficient swimmer"?

Apparently, it does so by creating a "virtual wall."

In some tropical waters like the Florida Keys mangrove forests, for snorkellers to stay safe, it’s not enough to not touch anything. It may not be a good idea to enter the water in the first place.

That’s because sometimes it seems that the water itself can sting, causing rashes on a snorkeller's skin.

In some tropical waters like the Florida Keys mangrove forests, for snorkellers to stay safe, it’s not enough to not touch anything. It may not be a good idea to enter the water in the first place.

That’s because sometimes it seems that the water itself can sting, causing rashes on a snorkeller's skin.

After combing through more than 2,000 articles and conducting a systematic review of the evidence for the use of heat or ice in the treatment of cnidarian envenomations, the team concluded that the majority of studies to date support the use of hot-water immersion for pain relief and improved health outcomes.

Box jellyfish have four morphologically different types of eyes. Two of these eye types called the upper and lower lens eyes, are camera type eyes with spherical fish-like lenses.