Ninety-five percent water, and older than trees.

Moon jellies are translucent, saucer-shaped animals with four pale horseshoe-shaped structures visible through the bell. These are reproductive organs. Their tentacles are short and delicate compared with those of lion's mane jellyfish.

Lion's mane jellyfish have a thick, often reddish, orange, or brownish bell surrounded by a dense mass of long trailing tentacles and oral arms. The largest individuals are found in colder northern waters.

Jellyfish tentacles contain microscopic stinging cells called nematocysts. Each contains a tiny coiled structure that can fire when triggered, injecting venom into prey or anything that touches the tentacle.

The mechanism is remarkably fast and largely mechanical, which is why a detached or stranded jellyfish can still sting.

Lion's mane stings usually cause immediate burning pain and red or raised welts, but serious reactions are uncommon. If stung, avoid rubbing the area and follow current local medical guidance for jellyfish stings. Seek urgent medical attention for breathing difficulty, severe swelling, widespread symptoms, or other serious reactions.

Jellyfish are weak swimmers compared with most fish. Their rhythmic bell pulses help them move through the water, but currents and tides often determine where they ultimately travel.

They have no brain, heart, bones, or conventional blood circulation. Instead, a simple nerve net coordinates their movements while their gelatinous bodies are made mostly of water.