The larval stage of polychaete worms (ragworms and lugworms) and of molluscs (winkles, limpets, whelks, mussels,etc. It looks like a spinning top encircled by bands of hairs (cilia) at top and bottom and one or two rows around the middle. In metaphorphosis the lower portion gradually lengthens and develops segments – the upper part becomes the head of the worm.
JOHN ANGUS 