semantic pointers
hyponym
yolk sac
yolk sac, vitelline sac, umbilical vesicle, vesicula umbilicus
amnion, amniotic sac, amnios
chorion
coelenteron
air bladder, swim bladder, float
air sac
air sac
saccule, sacculus
bladder, vesica
acinus
bursa
cisterna, cistern
pouch, pocket
vesicle, cyst
alveolus, air sac, air cell
pericardial sac
hypernym