Re: Newest Phylum?


Robert Maas, see http://tinyurl.com/uh3t wrote:
From: nos...@xxxxxxxxxx (Paul Ciszek)
Which phylum is believed to have emerged most recently?
That question isn't well-defined, because (1) phylum isn't a
natural thing, it's an artifact of our Linnean system of
nomenclature, a rather arbitrary division of life
I think that the Linnean phyla are still considered
monophyletic. Many classes and orders have been shown to be
polyphyletic. For instance, reptiles are not a clade. Alligators are
closer related to birds than to the other reptiles. Amphibians are not
a clade. Frogs and salamanders may have come from different species of
fish. However, chordates are definitely a clade. So asking which phyla
came first probably makes sense.

Actually Porifera are now believed to
be polyphletic with respect to other animal phyla, i.e. other
animal phyla are nested within Porifera.
That is extremely unlikely. Porifera are distinct from other
animals in that they do not have the same tissue cells as the others.
Porifera do not have muscle tissue, nerve tissue, connective tissue, or
the same type of epithial tissue. Even cnidarians have recognizable
animal tissues. So how can other groups of animals be nested in as part
of the Porifera? Porifera are also diblastic, like cnidarians.
Porifera definetely stand out from other multicellular organisms.
Do you mean that there are phyla of protista that are nested in
Porifera? Protista not generally thought of as part of the animal
kingdom anymore, although they used to be classified as such. However,
euglena and other protista have a dual animal/plant nature.


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Relevant Pages

  • Re: Newest Phylum?
    ... I think that the Linnean phyla are still considered monophyletic. ... animal phyla are nested within Porifera. ... Porifera do not have muscle tissue, nerve tissue, ... Animals develop from a blastula. ...
    (sci.bio.evolution)
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