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In deuterostomes, the original dent becomes the anus, while the gut eventually tunnels through the embryo until it reaches the other side, forming an opening that becomes the mouth. [1] It was originally thought that the blastopore of the protostomes formed the mouth, and the anus formed second when the gut tunneled through the embryo.
Enterocoely is the stage of embryological development of deuterostomes in which the coelom forms. [4] This type of coelom formation occurs in deuterostome animals, which for this reason are also known as enterocoelomates. By contrast, in protostomes, the body cavity is often formed by schizocoely. [4]
A cell can only be indeterminate (also called regulative) if it has a complete set of undisturbed animal/vegetal cytoarchitectural features. It is characteristic of deuterostomes—when the original cell in a deuterostome embryo divides, the two resulting cells can be separated, and each one can individually develop into a whole organism.
In deuterostomes, the developing embryo's first opening, the blastopore, becomes the anus, while the gut eventually tunnels through the embryo until it reaches the other side, forming an opening that becomes the mouth. This distinguishes them from protostomes, which have a variety of patterns of development.
The deuterostomes traditionally include the echinoderms, hemichordates, chordates, and the extinct Vetulicolia. The protostomes include most of the rest, such as arthropods, annelids, molluscs, and flatworms. There are several differences, most notably in how the embryo develops. In particular, the first opening of the embryo becomes the mouth ...
Pharyngeal clefts resembling gill slits are transiently present during the embryonic stages of tetrapod development. The presence of pharyngeal arches and clefts in the neck of the developing human embryo famously led Ernst Haeckel to postulate that " ontogeny recapitulates phylogeny "; this hypothesis, while false, contains elements of truth ...
In mammals, the term refers chiefly to the early stages of prenatal development, whereas the terms fetus and fetal development describe later stages. [2] [4] The main stages of animal embryonic development are as follows: The zygote undergoes a series of cell divisions (called cleavage) to form a structure called a morula.
These groups differ in several characteristics of early development; In deuterostomes blastula divisions is called "radial cleavage" because it occurs parallel or perpendicular to the major polar axis. In protostomes the cleavage is called "spiral" because division planes are oriented obliquely to the polar major axis.