AEBI 211 Lecture Notes - Lecture 6: Protostome, Deuterostome, Hemichordate
Document Summary
Polytomy = node on phylogeny where more than 2 lineages descend from single common ancestor: we don"t know relationships b/w the descendent lineages, descendent lineages speciated simultaneously. Protostomia: means first opening becomes mouth -- see slide 9: lophotrochozoan, generally possess trochophore larvae or lophophore i. e. platyhelminthes, mollusca, annelida, ecdysozoan, shed cuticle as they grow i. e. nematoda, arthropoda. Deuterostomia: means second opening becomes mouth i. e. chordata, echinodermata, hemichordata. Fate of blatospore : in greek , stoma = mouth, protos = first, deuteros = second. First mouth . i. e. the first embryonic opening (blastopore) becomes the mouth: blastopore becomes the mouth. Second mouth i. e. the second embryonic opening (no name) becomes the mouth: blastopore becomes the anus. Fate of cells : protostome, mosaic development characterizes most lophotrochozoan protostomes, cytoplasmic determinants are partitioned unequally, if separated, individual blastomeres still form structures that were dictated by the cytoplasmic determinants, needs all the blastomeres to develop properly.
