BIOL303 Chapter Notes - Chapter 5: Human Embryogenesis, Blastomere, Ctenophora
18 Nov 2015
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Gastrulation; formation of the 3 layers (endoderm, mesoderm and ectoderm) from the single layered blastula, early embryonic developmental stage! Sponges develop very differently from other animal groups, they are known as parazoans, however recent updates to taxonomy place them with metazoans. Three types of somatic cells, starting with the archeocyte which can differentiate into all other cell types. Individual cells of a sponge that passed through a sieve, can reaggregate to form new sponges. Reaggregation is species specific, if two are mixed from different species, each of the reaggregated sponges contains cells from only one species. Motile archeocytes therefore only collect cells from its own species: a cell and b cell -> a sponge and b sponge. Diploblasts, animals with two germ layers, ectoderm and endoderm with little to no mesoderm. Many cnidarians evolved independently of the mesoderm found in protostomes and deuterostomes: example, jellyfish contain striated muscles for propulsion, however different, in evolutionary aspect from vertebrates and insects.
