glenn
see http://www.flash.net/~mortongr/dmd.htm
for lots of creation/evolution information
> The online report betrays ignorance on the part of the reporter,
> so it's a little hard to tell what to make of it. (Family is not
> a good equivalent for phylum, Greenland has been demoted from the
> largest island status, and four other new phyla have been
> reported this century-Pogonophora, Gnathostomulida, Loricifera,
> and the cyclophorids, if I correctly remember the name of the
> lobster lip inhabitants.)
You remember correctly.
There's some debate about one of the
> purported 20th century phyla. Possible pogonophoran tube fossils
> are known, though I do not know if they have been analyzed in
> detail. Conversely, the DNA is very similar to certain annelids,
> and so some argue thay they should not be recognizd as a phylum.
> On the other hand, annelids may not be a single phylum.
To definitively say that one can't be in a different phylum because of a
similarity in DNA methodologically rules out incipient phyla. I would
suggest that phylum should be equivalent to bauplan. One of those borderline
cases is the sponges found by Vacelet and Boury-Esnault:
Occasionally, however, different body plans are not assigned different phyla
and this creates an appearance that phyla can't evolve. A case in point
concerns a deep-sea sponge which is classed with the Porifera in spite of
the fact that it has an entirely different body plan. Vacelet and
Boury-Esnault (Vacelet, J. and N. Boury-Esnault, 1995. “Carnivorous
Sponges,” Nature, 373:333-335, p. 335) relate:
"Our results raise fundamental questions about the validity of
characteristics used to distinguish the phyla of lower invertebrates. A
sponge is defined as a 'sedentary, filter-feeding metazoan which utilizes a
single layer of flagellated cells (choanocytes) to pump a unidirectional
water current through its body. Except for being sedentary, the cave
Asbestopluma and presumably all Cladorhizidae lack these basic sponge
attributes. In an extreme environment where active filter-feeding has a low
yield, cladorhizids have developed a mode of life roughly similar to that of
foraminiferans or cnidarians. Their feeding mechanism relies on passive
capture of living prey and on transfer of nutrients into the body through
intense cell migrations, the analogue of cytoplasmic streaming in
foraminiferan pseudopodia. This may be compared to the emergence of
macrophagy in abyssal tunicates, also accompanied by a reduction of the
filtering system although in Cladorhizidae the result is more extreme, with
a main body plan different from Porifera and resembling no other modern
anatomical design."
"Such a unique body plan would deserve recognition as a distinct
phylum, if these animals were not so evidently close relatives of Porifera.
Their siliceous spicules show clear similarities to several families of
poecilosclerid Demospongiae." In cases like that above, the lack
attribution of phylum rank for these 'sponges' hides the fact that the
Porifera may very well have given rise to an independent phyla. The only
real connection between the two groups are the spicules which act as
evidence of common descent. If the Cladorhizid sponges were to lose the
spicules, the connection between the two groups would be lost. Body plans
can obviously evolve.
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