| Name | Children | Media (from resource) | Traits |
|---|---|---|---|
| Anthoathecata Cornelius 1992 | 2 | 0 | 0 |
| Anthozoa Ehrenberg 1834 (anemones and corals) | 2 | 0 | 0 |
| Aphragmophora Tokioka 1965 | 0 | 0 | 0 |
| Apodida Brandt 1835 | 1 | 0 | 0 |
| Appendicularia | 1 | 0 | 0 |
| Gryphaea | 1 | 0 | 0 |
| Archypolycope Chavtur 1981 | 1 | 0 | 0 |
| Archypolycope punctata (Sars 1869) | 0 | 0 | 2 |
| Arcidae Lamarck 1809 | 1 | 0 | 0 |
| Chlamys livida | 1 | 0 | 0 |
| Argilloecia Sars 1866 | 2 | 0 | 0 |
| Argilloecia conoidea Sars 1923 | 0 | 0 | 1 |
| Argilloecia cylindrica Sars 1866 | 0 | 0 | 1 |
| Arrhis Stebbing 1906 | 1 | 0 | 0 |
| Arrhis phyllonyx (Sars 1858) (sea piglet) | 0 | 0 | 1 |
