Sunrise, Wizard Islet, British Columbia
Sunrise, Wizard Islet, British Columbia

Spring 2008

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Dr. Brian K. Penney

Goulet 2320

603 641-7149

bpenney@anselm.edu

Brian K. Penney 's web page

Lecture 1. The evolution of animal diversity

Updated: 1/15/08

Tuesday, February 12, 2008. Reading: 18.1-18.4; 18.22-18.23; 20.2-20.4; 20.9-20.10

  1. Animals are multicellular heterotrophs that feed by ingestion.

    • animals are multicellular heterotrophs that feed by ingestion

    • molecular and morphological evidence suggests they probably evolved from colonial protists called choanoflagellates

    • animals lack cell walls; instead, cells are held together by extracellular proteins and special intracellular junctions

    • most animals have muscle and nerve cells for sensation and coordinated movement


  2. Development typically proceeds through several stages:

    • fertilization and formation of the zygote

    • mitotic division to form a hollow ball of cells (the blastula)

    • infolding of one side of the blastula to form the gastrula.

      • Taxa in which this opening (blastopore) becomes the mouth are called protostomes;
      • Taxa in which this opening becomes the anus are called deuterostomes.
      • These groups also have distinctive patterns of early cell division and coelom formation
    • differentiation into tissue layers (see below).

    • some groups develop directly into adults, while others first form a larva, which then undergoes a major change in body form (metamorphosis) to become the adult.


  3. Embryonic tissue layers give rise to specific tissues.

    • ectoderm becomes the epidermis and nervous system

    • endoderm becomes the digestive tract and associated organs

    • mesoderm, where present, forms muscle, connective tissue, skeleton, circulatory system


  4. Levels of organization include:

    • cellular: where different cell types are specialized to particular functions

    • tissue: where cells of one or several types work together for common function, and are bound together with specialized junctions and basal lamina

    • organ: where different tissues are bound together in a structure for one purpose

    • organ system: where multiple organs coordinate for a particular function


  5. Symmetry

    • Symmetry is how an organism may be bisected to form pieces that are mirror images of each other.

    • asymmetrical organisms have amorphous forms that cannot be equally bisected

    • radially symmetrical organisms can be divided in any plane about at least one axis; these organisms have no "head", adapted to sedentary/planktonic life

    • bilaterally symmetrical organisms can only be divided in one plane; such organisms have a "head" which is specialized for sensing the environment


  6. Body spaces

    • An internal body space forms a mechanical barrier between endoderm and ectoderm, allows for the development and expansion of new structures, serves as a storage chamber for body products (e.g. gametes), provides a circulation medium, and serves as a hydrostatic skeleton

    • a true coelom is a fluid-filled space completely lined by mesoderm

    • a pseudocoelom is only lined with mesoderm on one side (usually the outside), and is most common in small animals

    • acoelomates have no internal body space, and must have spongy mesoderm that allows circulation


  7. Entire taxa are becoming threatened as invasive species spread to new environments


A printable syllabus, with course dates, required materials, grading and other policies can be found here.

A one page printable version of the schedule can be found here.

Copyright 2007-2008, Brian K. Penney

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