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.

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.