BIO 124 Lecture Notes - Lecture 12: Arthropod, Ribosomal Rna, Cnidocyte
21 Mar 2016
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Characteristics of animals: 59 million years ago starting at the end of the. Proterozoic, marine invertebrates appeared: 533-525 million years ago cambrian explosion, adaptation to terrestrial life. Amniotic egg: helps to protect egg and keep it moist, nutrients, animals evolved from colonial flagellated protists, related to the present-day choanoflagellates, cells similar to those found in sponges. Example: earthworms: pseudocoelomates, digestive tract from endoderm, pseudocoelom fluid filled space, muscle later from mesoderm, body covering from ectoderm. Example: nematode: acoelomates, digestive tract from endoderm, mesenchyme from mesoderm, muscle layer from mesoderm, body covering from ectoderm. Compare rrna of the small ribosomal subuit. The molecule is universal in all organisms. Also examine the hox genes: traditional phylogeny vs molecular phylogeny. At the earliest stage in evolution, a split occurred between parazoa and eumetazoa. There was also an early split between radiate and bilateria with most animal phyla belonging to the bilateria.
