- abaxillare
- abdomen
- abdominal scutes
- abingdoni
- Acanthochelys
- acoustic-jugular
- acrocentric
- acutirostris
- acutum
- adansonii
- adductor fossa
- adiutrix
- agassizii
- Agrionemys
- akinetic
- alabamensis
- alamosae
- albogulare
- albumin
- albumin-secreting glands
- alimentary
- allantois
- allele
- allometric
- allopatric
- allozyme
- alveolar
- amboinensis
- amnion
- amphicoelous
- amphipods
- Amyda
- anal scutes
- anamurensis
- anapsid
- anastomotic artery
- anatomy
- andersoni
- angular bone
- angulata
- angusta
- angustipons
- anisogamously
- anisogamy
- ankylosed
- Annamemys
- annamensis
- annandalii
- annulata
- annuli
- antebrachial scales
- anterior
- antigen-antibody reaction
- antrum postoticum
- Apalone
- apex
- appendages
- apposition
- arachnoides
- areola
- areolata
- areolus
- arizonense
- arnoldi
- arribadas
- arroyo
- artery
- articular bone
- articularis process
- articulation
- aspera
- Aspideretes
- ater
- atlantica
- atripons
- aubryi
- aurocapitata
- australis
- autotrophic
- axillary notch
- axillary scutes