BIOL 1002 Chapter : Ch 23 Invertebrate. 2/14 Notes
Document Summary
Most animals were present by the cambrian period (544 million years ago) Scientists studied these aspects of fossils to search for clues about evolution. Sponges are the only modern day animal that doesn"t have tissue. Each of their cells are specialized but do not communicate like tissue. Sponges and phyla arose from the same ancestor without tissue. Three types of animal tissues: ectoderm, mesoderm, endoderm. Symmetrical animals have an upper (dorsal) and a lower (ventral) surface. Radial-equal halves when divided by central axis: they have an ectoderm (covers body, they have an endoderm (lines hollow organs) They tend to be sessile or medusa. (fixed or free floating in a current) Bilateral symmetry-mirror image halves when divided through the midline: endoderm, mesoderm, ectoderm. Pseudocoelomate-fluid filled cavity not lined by mesoderm. (ex. Bilateral animals can be divided into 2 main groups. Sponge phylum: asymmetrical, lack organs, perforated, aquatic-oxygen extracted, nutrients removed, waste released.