In the late planula larva of
the hydrozoan Hydractinia, GLWamide-positive sensory
cells that innervate the apical plexus populate a belt
around the apical pole [114], which, by position, forms
part of the apical plate; MIP, a related Wamide neuropeptide that induces larval settlement in annelids, is secreted
into the apical plexus by apical organ cells [15].