CILIARY HOVERING IN LARVAL LANCELETS (=AMPHIOXUS)

Larvae of lancelets (=amphioxus) are of special interest because they figure prominently in debates about vertebrate origins (I), can someti mes grow into a giant ''amphioxides'' form (2, 3), have a puzzling rig ht-left asymmetry (4), and constitute a major zooplankton resource in parts of the Atlantic (5). By using improved methods (6, 7) to culture and observe healthy pre-metamorphic larvae in relatively deep contain ers, we demonstrated a prominent hovering behavior. The larvae spend m ost of their time suspended in midwater by metachronal beating of epid ermal cilia. The body is usually tilted at an angle such that the ante rior end and ventral side are oriented towards the water surface. This posture is maintained in the dark and in the light, although there is directional photosensitivity. Hovering may help account for the giant ''amphioxides'' and may be related to the curious asymmetry of the la rval body.