The sirens of Greek mythology are sometimes portrayed in later folklore as mermaid-like. But in the Odyssey they are described as birds with women's heads, not women with fish tails. Some languages use the same word for both bird and fish creatures, such as the Maltese word 'sirena'. Other related types of mythical or legendary creatures are water fairies (e.g., various water nymphs) and selkies, animals that can transform themselves from seals to humans.