No, those pictures weren't Photoshopped -- that sea creature has a horn like a unicorn. It's a narwhal. It might be hard to tell whether narwhals are whales or dolphins on first glance. Despite some overlapping physiology, however, narwhals clearly fall into the whale camp.
Meet the Narwhal
Narwhals -- Monodon monoceros, scientifically speaking -- are whales that live year-round in the Arctic, mostly near Canada, Greenland and Russia. They've got white, grey and black mottled skin and are slightly more streamlined and less flexible than their beluga brethren, according to a University of Washington scientist. They're migratory and travel in pods. Narwhals are related to bottlenose dolphins, belugas, harbor porpoises, and orcas, according to National Geographic. Regardless, they're whales -- one of only two members of the Monodontidae family -- and their closest living relative is the beluga whale.
Whales, Dolphins & Porpoises
Whales, dolphins and porpoises are all cetaceans -- warm-blooded, marine mammals. The term "whale" can refer to any cetacean, technically speaking, but is usually reserved for larger species. Dolphins are smaller cetaceans, while porpoises are are a similarly sized group of species without beaks who have spade-shaped teeth. When it comes to dorsal fins, cetaceans run the gamut from prominent to non-existent. Narwhals don't have dorsal fins. Because of the diverse traits among species, narwhals have more in common with dolphins than some distant-cousin whales, but, to reiterate, they're whales.
Teeth, Tusks & Feeding
All dolphins have teeth, but some whales have baleen, instead. This toothy detail is why it's easy to confuse narwhals for dolphins. Technically speaking, narwhals are odontocetes (i.e., toothed cetaceans), although they don't have any teeth in their mouths. Instead, narwhals have a horn that's really a tusk -- a specialized canine tooth -- that grows roughly eight feet from their upper-left jaws. This growth is unique among cetaceans. Most females don't have tusks, which is why their function probably isn't related to feeding and other non-sexed behaviors. Narwhals are among the most adept divers of the whale world, and subsist on a specialized, seasonal diet of deep-sea fish.
Finer Tusk Points
All narwhal's tusks grow in counter-clockwise spirals. Male narwhals probably use them to determine social rank, although they've never been observed using them for fighting or other aggressive behaviors. Most male narwhals have one tusk, although a small percentage have two. Size and morphology can vary greatly, although all tusks grow in counter-clockwise spirals. Female narwhals don't often have tusks, but a few do. Among those, a female dual tusk is considered quite rare, although there's at least one recorded case.