BIO 200 Lecture Notes - Lecture 18: Symmetry In Biology, Hydrostatic Skeleton, Deuterostome
23 Nov 2016
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The basal animals: over 95% of animals that we know of are invertebrates, over 75% are insects, only 60,000 species are considered vertebrates, constitute less that 1% - mammals. What makes an animal: multi-cellularity, heterotrophy - internal gut where digestion takes place, lack cell walls, motility, sexual reproduction - haploid gametes, characteristic embryonic development, specialized tissues. Fungi digest food externally, excrete enzymes outside of the body, and absorb the broken down molecules. Divide organisms in half through any 2-dimensional plant. The first form of symmetry to evolve was radial: sponges - lack true symmetry, grow in indeterminate masses, remaining animals - radial or bilateral, radial. Bilateral symmetry leads to cephalization - lead to evolution of brain area and dominance of the organism functioning: bileterians, top and bottom - dorsal (top) and ventral (bottom, anterior - head, posterior - tail. Diploblastic animals have two layers (jellyfish: ectoderm - outer.
