Selkie
From Star Trek : Freedom's Wiki
There is not a lot known about this unusual species other than that their natural habitat is water based. In order to survive in a Human like, oxygen/nitrogen based environment, Selkies must use dedicated breathing apparatus in order to maintain their natural bodily systems. In regards their actual origin however, various links seem to have established their kind within the legends of other cultures, although definitive data as to their precise origin, is not actually available at this time.