Jellyfish: The jellyfish is a marvel of nature that becomes a bit of a water hazard for swimmers, surfers and others hoping to enjoy the water on a hot day near a sandy beach. Below are facts about the wavy water dwellers.

First, they are not fish. They do not have gills, fins, scales or other features that are typically associated with fish. Instead, some experts advise dropping that part of the name and referring to the creatures as “Jellies.”

Next, the main shape of a jellyfish is called the medusa, named for the Greek mythological being who had snakes for hair.

Another interesting detail about jellies is that they can not intentionally move any way other than up and down. They move by quickly collapsing the medusa and propelling themselves upward by way of water displacement. Otherwise, their movements are determined by wind and currents.

Some jellyfish have been known to invade new territories by traveling in the ballast tanks of ships and entering the water in the new area when the ship jettisons the tanks.

Jellies are 95% made up of water, accounting for their graceful appearance among the waves and their goo-like appearance on land.

Jellies are simple organisms, made of two cell layers. The inner endoderm is the lining of their gut, while the outer layer is the ectoderm or epidermis. The stinging cells are located in the ectoderm.

Some jellies are transparent, while others are colorful and still others change color based on the saline levels in the water they currently inhabit.

There are at least 9,000 known species of Cnidaria, which is the phylum that includes jellies. These species inhabit any ocean and are of varying sizes. The largest is known as Nomura’s jellyfish, and it can grow to a size of six feet in width, from the size of a grain of rice, in a six-month period. That species can weigh as much as 200 pounds.