| Term | Definition |
| DISC | The VALVES of bivalves; in Pectinacea, the whole of the valve, excluding the AURICLES; see also: FLANK. | |
| DISCOIDAL | Round and flat, like a disk.; see also: DEPRESSED; LENTICULAR; PLANISPIRAL; SEMIDISCOIDAL. See other gastropod shapes. | |
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| DISCONTIGUOUS | Not touching each other, as in the whorls of some gastropods in which the whorls are separated and do not rest upon or touch each other; see: CONTIGUOUS; CONTINUOUS; WHORL, DISJUNCT; GYROCONIC. | |
| DISCONTINUOUS | Interrupted; not continuing intact from one point to another; see: CONTINUOUS. | |
| MARGIN, DISCORDANT | With margins of closed valves not in exact juxtaposition, but one overlapping the other; example: Anadara; see also: INEQUIVALVE. | |
| SEMIDISCOIDAL | Forming half of a circular disk; see also: DISCOIDAL. | |
| WHORL, DISCONTIGUOUS | Having subsequent WHORLS not touching the previous; = WHORL, DISJUNCT; = GYROCONIC. | |