The pilidium larva is the long-lived planktotroph characteristic of a monophyletic group of nemerteans, the pilidiophora.  It is increasingly clear that the pilidium is an independently-derived body plan; about the only clear case in which, within an extant phylum, a wholly new feeding form has been invented.  Using a combination of high-speed video and confocal and scanning electron microscopy, Richard Emlet, Svetlana Maslakova and I figured out how it eats, and our account was published in Frontiers in Zoology.  The movies are reproduced here.  These are identical to the files in the journal article (which is free).