Blastocoele is a biological term that refers to a fluid-filled cavity in the early embryonic stage of animals. However, there are various other synonyms for this term that are used in different animal species. For instance, in the case of birds and reptiles, the structure is referred to as the "subgerminal cavity." Similarly, in the case of amphibians, it is called the "blastocoel," and in the case of fish, it is known as the "yolk sac cavity." In some invertebrates, it is called the "archenteron," while in others, it is referred to as the "coelom." These alternate terms for blastocoele highlight the various terminologies used to describe similar structures in animals.