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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.
Deuterostomes (from Greek: lit. ' second mouth ' ) are bilaterian animals of the superphylum Deuterostomia ( / ˌ dj uː t ər ə ˈ s t oʊ m i . ə / ), [ 3 ] [ 4 ] typically characterized by their anus forming before the mouth during embryonic development .
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]
The second arch becomes the hyoid and jaw support. [5] In fish, the other posterior arches contribute to the brachial skeleton, which support the gills; in tetrapods the anterior arches develop into components of the ear, tonsils, and thymus. [7] The genetic and developmental basis of pharyngeal arch development is well characterized.
[2] [5] Fertilization is the fusion of gametes to produce a new organism. In animals, the process involves a sperm fusing with an ovum, which eventually leads to the development of an embryo. Depending on the animal species, the process can occur within the body of the female in internal fertilization, or outside in the case of external ...
Schizocoelous development often occurs in protostomes, [1] [5] [6] as in phyla Mollusca, Annelida, and Arthropoda. Deuterostomes usually exhibit enterocoely ; [ 7 ] however, some deuterostomes like enteropneusts can exhibit schizocoely as well.
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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.