A new species of leptostracan of the genus Nebalia, N. holothurophila, is described from southern California. The new species appears closely associated with the warty sea cucumber, Apostichopus parvimensis (H. L. Clark, 1913), although the exact nature of the relationship is unclear. The leptostracans were found in “transfer tubs” after the sea cucumbers were removed from artificial tidepools and placed in fresh seawater within these tubs. The new species differs from other leptostracans in southern California in having a combination of features not shared by any other species.