BIO 102 Lecture Notes - Lecture 19: Gastrovascular Cavity, Sea Anemone, Symmetry In Biology
Document Summary
Most current animal phyla were present by cambrian period (544 mya) Pre-cambrian fossils studied by examining anatomy, embryonic development, and dna sequences. We began looking at dna sequences to differentiate between organisms recently. Sponges are only current animals that lack tissue. (have ancestor without tissue) Symmetrical animals have dorsal (upper) and ventral (lower) surfaces. Radial/bilateral symmetry in animals with tissue (equal when cut in half, down the middle) Radial symmetry- divided in half by an angle as long as it goes through the central axis. All organisms that display this have two types of tissue (ectoderm and endoderm) and are considered diploblastic. Bilateral symmetry- can be divided in half by one plane down the middle, vertical. Have three tissue layers and are considered triploblastic. Bilateral organisms have an anterior and posterior region and move forward. Ectoderm- covers body, lines inner cavity nervous system. Organisms are either sessile (fixed in one spot) or drift around.
