Pedicellariae

Pedicellariae are spines found in various classes of the Echinoderms, and so modified as to form prehensile organs. The typical forms occur on the Sea-urchins; these consist of a small flexible stalk, at the free end of which are three pointed valves; these are hinged and can be closed round any foreign body with which they come in contact. Their grip is often so firm that the head of the' pedicellarise is usually torn from the stalk before the valves are relaxed. In some cases, as in the Heart-urchin (Spatangus), the pedicellarise is enclosed in a hollow in the plates of the external skeleton or test. In others there are four valves ; while in some forms, known as "globuliferi," the valves are atrophied and only the gland and stalk remain. In the Starfish the pedi cell arise are usually sessile - i.e. have no stalk - the valves are rarely more than two in number, and are pointed instead of hooked. In the common English Brittlestars pedicellariae are quite absent, but in some tropical species belonging to the Euryalida there are some simple forms which are probably rudimentary. The function of the pedicellariae is very doubtful, and probably differs in the different classes; they are unquestionably prehensile organisms and help in locomotion, seizing food, removing excreta, or may also be organs of touch and smell.