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Dr. W. Crone (303 FTZ, 629-7439, cronewil@hvcc.edu, http://www.hvcc.edu/academ/faculty/crone/index.html) 11/22/99

Text (7th ed.): aspects of Chs. 4 and 15

possible web sites: http://www.ucmp.berkeley.edu/clad/clad4.html (phylogenetic systematics)


(The Burgess Shale: the source of much information about the Cambrian"explosion" of animal phyla)

We have surveyed parts of the animal (and other) kingdoms so far. After Thanksgiving, will be talking about basic cell biology issues. This week, let's review where we've been and what's in store for our understanding of invertebrates. NOTE: not too many direct questions from this week will be on the final.


In week 1, we defined evolution as"changes in the gene pool over time."

gene: a particular stretch of genetic material (DNA) that codes for a particular protein.

Hence, looking at the genes (and proteins) of different organisms should give us insights into how they function and how they are related. Therefore, a major emphasis in today's zoology research is to build on the anatomical information of different animals by exploring their genetic sequences and how their proteins work. The broad picture that we've painted this semester in lecture holds up within this examination, but a lot of details await.

Single-celled and colonial protists (several phyla) highlight the complexities of life, even at the single-cell level. Sponges (Porifera) are still a side shoot of multicellularity. Jellies and comb jellies (Cnidaria and Ctenophora) are radially symmetrical animals emphasizing two main germ layers, whereas flatworms (Platyhelminthes) are organisms with three germ layers and bilateral symmetry. Roundworms and rotifers (Nematoda and Rotifera) demonstrate the biological adaptation of a pseudocoelom. The eucoelomate phyla we followed have very different appearances according to their means of support. Annelids use a hydrostatic skeleton, molluscs an incomplete exoskeleton, arthropods a complete exoskeleton, and echinoderms a dermal endoskeleton. Two invertebrates are the particular target of close examination:

Caenorhabditis elegans, a roundworm (Phylum Nematoda)

Drosophila melanogaster, an insect (Phylum Arthropoda)

(my own research, on the plant Arabidopsis thaliana, was in a similar vein of trying to correlate genetic changes from mutations with changes in developmental patterns)

Working out the molecular structures of these organisms gives researchers the tools to examine other invertebrates, as well as ourselves. Using molecular information, as well as structural information, to test hypotheses of relationships via cladistics (e.g., those branch diagrams at the chapter ends) should help us to"view" the history of life on earth from the first appearances of these phyla in the fossil record to today. Continued understanding of these organisms can also help us solve puzzles such as how to treat parasites such as those involved with malaria, whose genetic sequence should contain clues to its vulnerabilities.1,2

  1. X-Z Su, et al.. 1999. A genetic map and recombination parameters of the human malaria parasite Plasmodium falciparum. Science: 286: 1351-1353.
  2. http://www.malaria.org

|main page| |background| |03028: Physiology| |03048: Anatomy|

|03050: Invertebrate Zoology| |03051: Vertebrate Zoology| |03074: Economic Botany|


Please send comments and questions to: cronewil@hvcc.edu


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Copyright 1999 by Wilson Crone

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This page updated on November 22, 1999