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 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. During gastrulation, protostomes embryos' mouth was given first by the blastopore while the anus was formed later and vice versa for the deuterostomes. As examples :

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  Squids are protostomes.
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  Sea urchins are deuterostomes.