Perspectives of Biology 113 Notes
Perspectives of Biology 113 Notes
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This 6 page Class Notes was uploaded by charlotteee on Wednesday June 1, 2016. The Class Notes belongs to at University of Rochester taught by Bickel in Spring 2016. Since its upload, it has received 9 views. For similar materials see Perspectives in Biology 113 in Biology at University of Rochester.
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Date Created: 06/01/16
Molecular Phylogeny of Animals: Zooming in on most basal or primitive animals: Outgroup are choanoflagellates 1. Porifera: suspension feeders (most think sponges are basal or forming the bottom layer/group); Poriferans are commonly referred to as sponges. An early branching event in the history of animals separated the sponges from other metazoans. Sponges have CHOANOCYTE cells that resemble CHhoanoflagellates/outgroup. As one would expect based on their phylogenetic position, fossil sponges are among the oldest known animal fossils, dating from the Late Precambrian. Larva can swim until they become suspension feeders and just sit there. Sponges do not seem to have true tissues or organs or significantly differentiated cells. NO symmetry 2. Comb Jellies (Ctenophora): First organism have true tissues With the Cnidaria out of the way, the next big clade on the animal tree is the Acrosomata, a clade that combines the Ctenophora and the Bilateria. Ctenophores fall into two groups, the tentacle-bearing Tentaculifera and non-tentacle-bearing Atentaculata. They’re all marine predators, engulfing prey with their body. **THEY HAVE Radical Symmetry which seems unlikely for a basal species! Placozoa: the most primate looking animals, but probably not basal (only one described species); Historically placozoans have been placed at the base of the metazoan tree of life because of the very simple morphology with only five described cell types and the lack of any kind of ECM, nerve cells, and axes. Early molecular phylogenetic studies based on small and large ribosomal subunits (18S and 28S) have placed Trichoplax at various positions, including relationships to (i) Cnidaria, (ii) Ctenophora, and (iii) even to Bilateria Cnidaria: radical symmetry, and have tissues (groups of similar cells that carry out function) Bilateria: bilaterally symmetrical if we split ourselves in half, we have an arm on each side, etc. Germ types: seeds of different tissue types Diploblastic: 1. Body wall develops from embryonic germ layers- ectoderm (skin, nervous system) and endoderms (on the inside, form the digestive system/cavity) and persists as such in adult. Mesoderm (form muscle tissue and some organs) 2. Non- cellular, gelatinous mesogloea is present in between ectoderm and endoderm. 3. Coelom is absent, e.g. Hydra (coelenterates), sponges (Porifera). Triploblastic: 1. Body develops from 3 germ layers- ectoderm, mesoderm and endoderms. 2. Mesogloea is absent and mesoderm is present. 3. Coelom is present, e.g. platy-helminthes, annelids, arthropods, mollusks, echinoderms and choradates. None: sponges and placozoa do not have symmetry Radial: dorsal, ventral (only one body axis symmetrical) ctenophores and cnidarians Bilateral: dorsal-ventral, anterior-posterior, left- right Protosomes: develop mouth first; a multicellular organism whose mouth develops from a primary embryonic opening, such as an annelid, mollusk, or arthropod. Ecdysozoa (The Ecdysozoa comprise one of the major groups within the animal kingdom, and it is also the largest since it includes both the arthropods (insects, spiders, and crustaceans) and the nematodes. The Ecdysozoa is one of the two large subdivisions within the Protostomia, a group in which the mouth develops from the first opening to develop in the embryo. In turn, the Protostomia belongs to a larger group within the Animalia called the Bilateria, because these animals are bilaterally symmetrical, with a left and a right side to their bodies): including arthropods (are segmented and different things develop on different segments; lots of specialization on different segments) and nematodes (Nematodes were once classified with a very large and heterogeneous cluster of animals grouped together on the basis of their overall worm-like appearance, simple structure of an internal body cavity called a pseudocoelom, and the lack of features such as cilia and a well-defined head that are found in most animals). Deuterostomes: develop anus first; an animal whose mouth develops from a second opening in the early embryo, opposite to the initial opening blastopore of the rudimentary gut. Chordates and echinoderms are deuterostomes. (PROTOSTOMIA = Spiralia and Ecdysozoans) Spiralia: includes Molluscs, Annelids, Brachiopods, Platyhelminthes and several other smaller phyla. All shared one aspect called Holoblastic Spiral Cleavage (found in flatworms, annelids and molluscs Mollusca: Molluscs are a clade of organisms that all have soft bodies which typically have a "head" and a "foot" region. Often their bodies are covered by a hard exoskeleton (Chitin), as in the shells of snails and clams or the plates of chitons. Annelids: Segmented worms make up the Phylum Annelida. The phylum includes earthworms and their relatives, leeches, and a large number of mostly marine worms known as polychaetes. Various species of polychaete are known as lugworms, clam worms, bristleworms; Annelida is a group commonly referred to as segmented worms Platyhelminthes (flatworms): The simplest animals that are bilaterally symmetrical and triploblastic (composed of three fundamental cell layers) are the Platyhelminthes, the flatworms. Flatworms have no body cavity other than the gut (and the smallest free-living forms may even lack that!) and lack an anus; the same pharyngeal opening both takes in food and expels waste. Because of the lack of any other body cavity, in larger flatworms the gut is often very highly branched in order to transport food to all parts of the body. The lack of a cavity also constrains flatworms to be flat; they must respire by diffusion, and no cell can be too far from the outside, making a flattened shape necessary.
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