The narwhal has a long, straight tusk. It is a type of whale.
The narwhal, which is a type of whale, has a long, straight tusk.
The dugong is sometimes called a sea cow. It is a kind of mammal.
The dugong, which is a kind of mammal, is sometimes called a sea cow.
Last weekend we went to the aquarium. It now has a collection of seahorses.
Last weekend we went to the aquarium, which now has a collection of seahorses.