acephalocyst

n. [ Gr. 'ake`falos without a head + ky`stis bladder. ] (Zool.) A larval entozoön in the form of a subglobular or oval vesicle, or hydatid, filled with fluid, sometimes found in the tissues of man and the lower animals; -- so called from the absence of a head or visible organs on the vesicle. These cysts are the immature stages of certain tapeworms. Also applied to similar cysts of different origin. [ 1913 Webster ]