| Substrate Origin | Biogenic Substrate |
| Substrate Class | Shell Substrate |
| Substrate Subclass | Shell Rubble |
| Substrate Group | Clam Rubble Crepidula Rubble Mussel Rubble Oyster Rubble |
| Definition | Substrate that is dominated by living or non-living shells forming Rubble, with a median particle size of 64 millimeters to < 4,096 millimeters in any dimension (Cobbles and Boulders). Particles may be either loose, individual shells (whole or broken) or—particularly in the larger Rubble sizes—cemented, conglomerated, or otherwise attached so as to form Boulders of consolidated shell material. The presence of Shell Rubble is noted in this subclass (and in the following groups). The presence of living organisms is described in the BC. |