| Abstract: | Light and electron microscopy reveal that simple receptor cells in the jaw epithelium of sea urchin pedicellariae are connected by nerve tracts to the neuropile that coordinates jaw movements. The muscles responsible for jaw opening and closure and for flexion of the stem are all innervated in this neuropile. At least two types of vesicles occur at the simple synapses between neurone profiles and at neuromuscular junctions. The muscles include both striated and smooth fibres; however, their distribution varies according to pedicellaria type, and an unexpected arrangement exists in trifoliate pedicellariae. |
