Final answer:
The formation of the blastula involves critical developmental characteristics such as being diploblastic or triploblastic, with the latter further classified as protostomes or deuterostomes, and based on body cavity development as acoelomates, pseudocoelomates, or eucoelomates.
Step-by-step explanation:
During the formation of the blastula, several developmental characteristics determine the classification of an organism. Among these characteristics, animals are categorized as diploblastic or triploblastic based on the number of germ layers formed during gastrulation. Diploblasts have two germ layers, the endoderm and ectoderm, while triploblasts develop an additional mesoderm. Moreover, triploblasts can be classified as either protostomes or deuterostomes based on the fate of the blastopore. Protostomes usually exhibit spiral cleavage and form the mouth from the blastopore. Conversely, deuterostomes exhibit radial cleavage and the anus forms from the blastopore, with the mouth forming at the opposite end. Triploblasts are further categorized based on the type of body cavity formation into acoelomates (no body cavity), pseudocoelomates (body cavity not entirely lined with mesoderm), and eucoelomates (coelom entirely lined with mesoderm).