![]() ![]() Echinoderms are a large group of metazoans that constitute with the hemichordates the clade of the ambulacrarians, within the deuterostomes. Because of such diversity, the evolutionary history of nervous system in metazoans has been heavily debated. Nervous systems in metazoans range from simple nerve nets to complex centralized organs. The other scenario (II) claims the amphistomy as being ancestral,įrom which deuterostomy and protostomy evolved by closure of theīlastopore from the posterior to anterior direction (protostomy) orįrom the anterior to posterior direction (deuterostomy). Mouth determination from the blastopore (intermediate stage small). Proposing the abbreviation of the anterior movement of theīlastopore (dotted bright arrow) by a molecular separation of the The evolution of deuterostomy is using the protostomy as ancestral, InĪmphistomy, the blastopore elongates and closes laterally withīoth ends giving rise to the mouth and anus. Site from the former blastopore in the anterior of the embryo. ![]() The blastopore stays at the posterior site of the embryo and eitherĬloses or gives rise to the anus. The anus (A), if present, is formed at aĭifferent site at the posterior end of the embryo. The blastopore (bright in all fi gures) is displaced from posterior toĪntero-ventral by morphogenetic movements (bright arrow), and Protostomy, deuterostomy, and amphistomy andĮvolutionary scenarios about the direction of change. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |