Swimming into view like an oceanic Halloween specter, today"s "sea angel" is one of about 3,000 sea slug species. Sea slugs can be found in all the oceans and seas of the world. Scientifically known as nudibranchs, sea slugs are mollusks and today is the day the world celebrates them. What, you didn"t know? Perhaps that"s because technically it"s the birthday of the premier authority on all things related to sea slugs, Terry Gosliner. Gosliner has identified nearly half of the known sea slug species in the world, has written 150 scientific papers about them, and has personally named around 350 individual species. "Everything about them just piques the imagination," he says. So, we"re saying "Happy birthday, Terry" by taking a moment to examine the sea angel.