BIOL 2P92 Lecture Notes - Lecture 8: Gastrovascular Cavity, Cnidocyte, Body Plan
6 Feb 2017
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Sponges, placozoa, cnidaria and ctenophora are monophyletic groups. Alternative phylogenies for sponges and basal metazoa: phillippe (2009) Split with placozoa as the sister group to bilateria: over time in molecular systematics, the more data accumulate, the more answers you get that constantly reoccur, some phylogenies built on gene expression, built. All members of cnidaria have (plesiomorphic): radial, polypoid body form. Symmetry of body forms is an important change in evolution used in creating phylogenies. Radial symmetry: same view from the top. Bilateral symmetry: symmetrical on a longitudinal plane: cnidocytes (stings, planula larva (flat, mouth surrounded by solid tentacles. Major kinds of body forms: polyp. Most cnidarians have both body forms that include: gastrovascular cavity (somewhat hollow, tentacles, epidermis and gastrodermis (layer of tissue outside and inside) Primitive form: mesoglea (jelly has cells wandering through it) Hydra body form is common in all animals: sits and waits for food to come to it.
