What is Classification?
The classification of organisms is the attempt by biologists to arrange
organisms in categories and groups that reflect phylogeny -- the
evolutionary history of a group of organisms. There are two types of classification,
cladistic and classic. Cladistic classification is concerned only with the order of branching in
phylogenetic lingeages. It uses cladograms, which are a serious of branches that divide at homologous
features, to classify subjects. The homologous features come in two types, primitive characteristics,
that already exsisted in the phylogeny, and derived characteristics, which are homologous features that
are unique to the common ancestor. In classic classification, taxonomists use degrees of divergence in
lineages to classify.
To conclude our Classification Lab we were asked to, by our teacher, to answer a
few questions about the differences in the animal line, here they are:
- The first division is between Parazoa and Eumetazoa.
- Parazoa is a division of animal line which includes only sponges,
everything else is Eumetazoa. The difference between the two is that
Parazoans have no true tissue, in
fact, you can push them through a filter or screen and their cells will join back up
up at the other side.
- The division between radial and bilateral animals is second.
- The difference between a radial and bilateral animal is in their
symmetry. A bilateral animal, like you or me, can be divided into two
halves. The cnidarians, the only radial animals, have many such sections
which all revolve around one point. An animal is considered bilateral or
radial by the way they develop, e.g. the echinoderms, which appear as an
adult to be radial, are, because they develop bilaterally, a
- The next division in Kingdom Animalia is the develpment of the body
- Flatworms have only one body cavity, and it does not go through their
entire body. When they eat and excreat they use the same opening.
Roundworms have a sudocoelem which suspends their digestive tracts in
fluid. The roundworm's digestive tract goes all the way through it, so
what it eats is execrated through an anus instead of being excreted
through its mouth. A earthworm has a true coelem, which means that its
digestive tract is held in place by tissue, instead of floating freely.
All animals that are more complex than a round worm have a coelem.
- The remaining animals are split into deuterostomes and
- When deuterostomes develop their cells line up in such a way that
in the eight cell stage they can be divided in half with no cells being
destroyed. The protostomes develop spiraly and subsequently cannot be
divided like that. In a deuterostome the mouth developes from the
blastopore, but a protostome developes the anus from the blastopore.
The mesoderm develops from only the endoderm (the blastopore) in a
deuterostome, whereas in a protostome the mesoderm developes from both the
endoderm and exoderm.