The motor innervation of the oral plate ligament in the brittlestar Ophiura ophiura (L.)

Summary The innervation of the connective tissue ligaments between the oral plates on the arm of a brittlestar by small branches of the hyponeural motor system is described. These branches arise from the hyponeural part of each segmental ganglion and pass laterally round the nerve cord and then orally across the epineural sinus to penetrate a small intersegmental node of juxtaligamental tissue located centrally. The endings of the nerve branches contain numerous small agranular vesicles and make chemical synapses onto the juxtaligamental cells. Processes from the juxtaligamental cells containing large granular vesicles ramify amongst the connective tissue of the oral ligaments. This innervation is associated with rapid changes in the stiffness of the connective tissue.