Axis purely horny, composed of carbonate hydroxylapatite with narrow but distinct chambered central chord; cortex little loculated, if at all. Polyps fully retractile, some forming low calyces (polyp-mounds), scattered or biserially disposed. Axis/polyp coenenchyme moderately thick, packed with spindles and capstans with regular belts of tubercles; in certain genera modified into disc spindles, scaphoids, or unilaterally spinous forms. Anthocodial armature weak, in form of crown composed of flat rodlets with scalloped edges, or lacking entirely. Colonies of diverse form, from unbranched to pinnate, closely reticulate or foliate.