Some before the dinosaurs,any better answers?
They live in water, some species live in salt water, others live in fresh water.
There are many species of puffer fish. All species live in the water most live in saltwater though there are some species that are brackish and can live in fresh water as well.
some species live and hunt on land, while some species hunt in shallow water.
Some species may, will other species live on land
There are lots of species, and most are marine (live in the ocean). Some live in brackish estuaries, there are a few species that live in fresh water as adults but the ocean as larvae, and there are a few species that live totally in fresh water.
yes , they do live under water :) ]
Certain species of slugs live on land, and certain species live in the water. No species of slug can live in both.
No as reptile are not amphibians so they wont spend a lot of time in water. All the species of gecko are from land based areas so there wouldn't be sufficient space for them to evolve to live under water. If you are looking for a pet that does live under water then try amphibians. Your best bet is an axolotl. They are an endangered species from just two lakes in Mexico but have been captive-bred since the 1830s. They spend all there time in water as they stay in larvae form. Even so in larvae form they can still breed like usual.
Jellyfish do not live that far under the water's surface. These jellyfish typically only live a few feet under the water.
They don't choose to live in water, they have to live in water. Certain species can live for an extended amount of time out of water, but they have to return to water to survive.
The wet kind. Some species live in fresh water, others live in salt water.
They mostly live in salt water, but a few species live in freshwater ponds and lakes.