ABSTRACT
The term rostrate was introduced by Mortensen in 1907 to describe pedicellariae in spatangoids. These organs resemble tridentate pedicellariae but they have arching valves. Unlike the main categories of echinoid pedicellariae no clear diagnosis of the rostrate form exists and some confusion arises because tridentate organs in certain regular echinoids appear superficially similar. This work examines the detailed morphology of the valves of rostrate pedicellariae using light and scanning electron microscopy and compares the shapes and dimensions of their component parts with tridentate pedicellariae. The data shows considerable differences which warrant the recognition of rostrate pedicellariae as a distinct form.
