| These include trilobites, clams, soft bodied and hard-bodied sponges, sea cucumbers, sea lilies, worms, snails, brachiopods, jellyfish, etc. |
| The Atdabanian epoch saw the emergence of the calcareous shelled Nisusiidae, the earliest and most primitive of the articulate brachiopods. |
| Billingsella in contrast has a laminar secondary shell characteristic of other, quite distinct, groups of articulate brachiopods. |
| Terebratulids are one of the only two living orders of articulate brachiopods, the other being the Rhynchonellida. |
| The brachidium is a structure which supports the lophophore, the feeding organ of brachiopods. |
| Conflicting evidence on the position of brachiopods in metazoan phylogeny exists. |
