Achaeta, [445]

Acholoe, [297]

Aciculum, [247]; fossil, [302]

Acmostoma, [50]

Acoela, [42];

occurrence and habits, [43];

reproduction, [47];

classification, [49]

Acotylea, [16] f., [17], [18]

Acrorhynchus, [49];