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In both deuterostomes and protostomes, a zygote first develops into a hollow ball of cells, called a blastula. In deuterostomes, the early divisions occur parallel or perpendicular to the polar axis. This is called radial cleavage, and also occurs in certain protostomes, such as the lophophorates.
The embryological origin of the mouth and anus is an important characteristic, and forms the morphological basis for separating bilaterian animals into two natural groupings: the protostomes and deuterostomes. In animals at least as complex as an earthworm, a dent forms in one side of the early, spheroidal embryo.
[4] [1] It is now known that the fate of the blastopore among protostomes is extremely variable; while the evolutionary distinction between deuterostomes and protostomes remains valid, the descriptive accuracy of the name protostome is disputable. [1] Protostome and deuterostome embryos differ in several other ways.
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.
Some hypoblast cells migrate along the inner cytotrophoblast lining of the blastocoel, secreting an extracellular matrix along the way. These hypoblast cells and extracellular matrix are called Heuser's membrane (or the exocoelomic membrane), and they cover the blastocoel to form the yolk sac (or exocoelomic cavity). Cells of the hypoblast ...
The eukaryotic cell cycle consists of four distinct phases: G 1 phase, S phase (synthesis), G 2 phase (collectively known as interphase) and M phase (mitosis and cytokinesis). M phase is itself composed of two tightly coupled processes: mitosis, in which the cell's nucleus divides, and cytokinesis, in which the cell's cytoplasm and cell membrane divides forming two daughter cells.
Animals called protostomes develop through schizocoely for which they are also known as schizocoelomates. 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 ...
Bilaterians can be divided, based on events that occur very early in embryonic development, into two groups called protostomes and deuterostomes. [20] Deuterostomes include vertebrates as well as echinoderms and hemichordates (mainly acorn worms). Protostomes, the more diverse group, include arthropods, molluscs, and numerous types of worms ...