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Protostomes are the first species to develop before Deuterostomes and most coelomates are Protostomes. What distinguishes Protostomes from Deuterostomes is the type of opening that develops from the blastopore. For Protostomes a mouth forms and for deuterostomes an anus form. Another key feature that distinguishes them is that Protostomes and deuterostomes have determinate and indeterminate cleavages respectively. Protostomes are the outgroup because of their blastopore development. The earliest form of deuterostomes are echinoderms such as sea stars and sea cucumbers. Echinoderms are mainly distinguished by their spiny skin and water vascular system, which is a multifaceted system that transportation, disposal of waste andlocomotion. They also all have pentaradial symmetry although it is not as obvious in some echinoderms. Ossicles also give them protection and rigidity, and this is extremely useful in a moving aquatic environment. We see that the next evolutionary development is the presence of