ambulacra ria

[From ambulacrum (q.v.).] A name given to the groups or series of the coronal pieces in an echinus, which are perforated. ( Griffith's Cuvier, vol. xii., p. 541.) ăm-bu-lā-crŭm (pl. ăm-bu-lā-crạ), 8. [Lat, ambulacrum = a walk planted with trees; from ambulo = to walk.] Zool. Plur.: Ambulacra are the perforated spaces arranged in regular lines from the apex to the base of an Echinus, or Sea-urchin. Through these, when the animal is living, the tubular feet or tentacles are protruded.