Acanthochitonidae – Acanthochitoninae (chitons)
Aclididae (aclidids)
Acteonidae – Acteoninae (acteons)
Actinocyclidae (sea-slugs)
Aegiretidae (sea-slugs)
Aeolidiidae (sea-slugs)
Aglajidae (sea-slugs)
Amathinidae (amathinas)
Amphibolidae (air-breathers)
Amphitretidae (octopuses)
Anabathridae (false rice-shells)
Anatomidae (slit-shells)
Anomiidae – Anomiinae (jingle-shells)
Anomiidae – Placunanomiinae (saddle-oysters)
Aplysiidae – Aplysiinae (sea-hares)
Architectonicidae – Architectonicinae (sundial-shells)
Architectonicidae – Heliacinae (sundial-shells)
Architeuthidae (squid)
Arcidae – Anadarinae (ark-shells)
Arcidae – Arcinae (ark-shells)
Argonautidae (paper-nautiluses)
Arminidae (sea-slugs)
Assimineidae – Assimineinae (assimineas)
Ataphridae (ataphrids)