What is the narwal in reality?

Professor Pierre Aronnax embarks upon his epic journey beneath the sea in hope of catching sight of a giant narwhal. A narwhal is a toothed whale, famous for the long tusk that protrudes from its bulbous head. Narwhals are medium-sized creatures, but the one that Aronnax goes looking for is an absolute behemoth.
The professor encounters what he thinks is the giant narwhal, but he probably wishes he'd stayed at home, because his vessel is completely wrecked by the fearsome beast. Thankfully, Aronnax survives and is amazed to discover that the giant narwhal isn't really a narwhal at all— it isn't even an animal. It's actually a submarine called the Nautilus. Captain Nemo is in charge of the vessel and invites Aronnax aboard. Thus begins a truly incredible journey full of strange sights and even stranger creatures—veritably jam-packed with adventure.