ABSTRACT
A preliminary survey of the skeletal features of ophiuroid arm spines has revealed a surprising diversity across the class. The base of the spine has a concave bearing surface, a slot for the spinal nerve, and on its oro-proximal edge a projection or plug which fits into a socket in the tubercle. The spinal muscle inserts into the outer face of this plug. Within the spinal ligament there are many cell processes containing electron-dense granules. The arm spine joints of Ophiocomina are adapted for extreme inclination in an aboro-distal direction. The distal region of an arm is draped across its own base to form a loop which is then dragged distally along the arm to collect a bolus of particles that is eventually transferred to the mouth.
