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Protostome and deuterostome embryos differ in several other ways. Secondary body cavities ( coeloms ) generally form by schizocoely , where the coelom forms out of a solid mass of embryonic tissue splitting away from the rest, instead of by enterocoelic pouching , where the coelom would otherwise form out of in-folded gut walls.
In humans (a deuterostome), the development proceeds differently. The buccopharyngeal membrane is created in the foregut and is perforated during the fourth week of human development, creating the primitive mouth, whereas the cloacal membrane is created in the hindgut and is perforated during the eighth week of human development, creating the ...
[21] [22] That implies that the protostome and deuterostome lineages split long before Kimberella appeared, and hence well before the start of the Cambrian 20] i.e. during the earlier part of the Ediacaran Period (circa 635-539 Mya, around the end of global Marinoan glaciation in the late Neoproterozoic). It has been proposed that the ancestral ...
English: This diagram is showing the difference of the two major types of coelomates: the protostomes (molluscs, annelids, arthropods, ...) and deuterostomes (echinoderms, vertebrates, ...). These groups differ in several characteristics of early development; In deuterostomes blastula divisions is called " radial cleavage " because it occurs ...
The distinction between protostomes and deuterostomes is based on the direction in which the mouth (stoma) develops in relation to the blastopore. Protostome derives from the Greek word protostoma meaning "first mouth" (πρῶτος + στόμα) whereas Deuterostome's etymology is "second mouth" from the words second and mouth ...
Its appearance is a matter of debate, for no representative has been (or may or may not ever be) identified in the fossil record.Two reconstructed urbilaterian morphologies can be considered: first, the less complex ancestral form forming the common ancestor to Xenacoelomorpha and Nephrozoa; and second, the more complex urbilaterian ancestral to both protostomes and deuterostomes, sometimes ...
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Early in development, deuterostome embryos undergo radial cleavage during cell division, while many protostomes (the Spiralia) undergo spiral cleavage. [143] Animals from both groups possess a complete digestive tract, but in protostomes the first opening of the embryonic gut develops into the mouth, and the anus forms secondarily.