- Astrolonche pectinata
- Astrolonche pinnata
- Astrolonche serrata
- Astrosphaera hexagonalis
- Athorybia rosacea
- Atlanta californiensis
- Atlanta echinogyra
- Atlanta fragilis
- Atlanta frontieri
- Atlanta fusca
- Atlanta gaudichaudi
- Atlanta gibbosa
- Atlanta helicinoides
- Atlanta inclinata
- Atlanta inflata
- Atlanta lesueuri
- Atlanta meteori
- Atlanta oligogyra
- Atlanta peresi
- Atlanta peroni
- Atlanta plana
- Atlanta rosea
- Atlanta tokiokai
- Atlanta turriculata
- Atlanticella bicornis
- Atlanticella craspedota
- Atlanticella planctonica
- Atolla chuni
- Atolla parva
- Atolla vanhoeffeni
- Atolla wyvillei
- Augaptilus anceps
- Augaptilus glacialis
- Augaptilus longicaudatus
- Augaptilus megalurus
- Augaptilus spinifrons
- Aulacantha cannulata
- Aulacantha scolymantha bathybia
- Aulacantha scolymantha scolymantha
- Aulastrum mirabile
- Aulastrum monoceros
- Aulastrum spinosum
- Aulatractus fusiformis
- Auloceros arborescens birameus
- Auloceros arborescens dichodendrum
- Auloceros arborescens irregularis
- Auloceros arborescens subelegans
- Auloceros arborescens trigeminus
- Aulographis bicurvata
- Aulographis furcula