Hello Gijs,
 
     I'm not really sure as to the placement of some of the unicellular
     forms, including the flagellates, or the reasons for lumping and
     splitting at some level.  When I was in school (late pleistocene) it
     was really a bummer that some flagellates, e.g. Euglena, had
     chloroplasts like plants.  There are those that would erect a phylum
     for the Euglenophyta, and there are probably lots of schemes among the
     experts.  The important thing to remember is that the structure and
     function of all of the lower algae (e.g. diatoms and dinoflagellates)
     are pretty well understood, even if the evolutionary relationships
     might be in question.  At these levels, there are certain very basic
     determinators, largely structural, biochemical, and physiological,
     that separate the groups.
 
     The viruses are just that:  viruses -- organized bundles of proteins
     and nucleic acids, mainly, that replicate intracellularly (within
     another's animal or plant cells) and depend on the host cell to
     perform many necessary biochemical functions.  Not an animal!
 
     My original point was that even at the highest levels of organization
     (forget genus and species) there have been controveries and there were
     will be more.  What bemuses me is that some amateur "biologists" are
     wont to discuss the minutae of binomial nomenclature and such things
     without a feel for the bigger picture and the biological principles
     that unite all critters.  Taxonomy is important and necessary, but it
     becomes a lot more fun within the greater realm of science.
 
     Yes, there are two fundamental embryological types resulting in
     different body plans in the higher animals -- the protostomes and
     deuterostomes.  They have different cell cleavage patterns (spiral and
     radial), and different ways that that they form the various germ
     layers in the older embryo which later become the various organs.
     Chordates and echinoderms are deuterostomes.  Molluscs and arthropods
     are protostomes.
 
     Thanks for the questions.
 
     Any good recent college biology text will give you a lot more of the
     details.
 
     Bob Avent
     Minerals Management Service
 
 
______________________________ Reply Separator _________________________________
Subject: Bacteria
Author:  "Gijs C. Kronenberg" <[log in to unmask]> at ~smtp
Date:    3/27/98 1:56 PM
 
 
Dear Dr. Avent,
 
Thanks for this info; apparantly I back some years with my knowledge. It
also appears that some unicellular groups are now placed more
satisfactoraly (e.g. flagellates). I recall that theyonce were in a group
which was best defined as: non animal, non plant and not fungi. Am I still
correct in believing that virusses are not classified as living organisms?
The part down from Kingdom I already knew..... (no alterations as far as I
can see)
Yet there might be a splitting up in the Kingdom Animalia, as there appears
(as far as I can remember) a fundamental difference after the third or
fourth cell division (is this the correct American way of expressing) after
fertilization. This would for instance imply that we are more related to
sea urchins that to molluscs.
 
Gijs C. Kronenberg