The picture above shows mosquito larvae suspended in water.

Mosquitoes require a body of still water as this is where the eggs develop.

Mosquito larvae of most species (but not all) have a prominent breathing siphon (tube). You can see this in the picture. The larvae rest suspended diagonally from the water surface, while the end of their siphon tube penetrates the surface, this allows the larvae to access their air supply. It works a bit like a snorkle.

Anopheles are however one of the species which don't have these siphons. Instead they lie suspended horizontally (parallel to the water's surface). They have small hairs which keep them attached to the water's surface and therefore able to breathe. You can see these on the diagram on the right.

Source: CDC Public Health Image Library