[Taxacom] Animalia or Metazoa?

Stephen Thorpe s.thorpe at auckland.ac.nz
Fri Jul 24 01:31:14 CDT 2009

Thanks Ken - that clarifies for me current thinking on the  
phylogenetic relationships between sponges and the rest of the, er,  
Metazoa (?=Animalia). It just leaves open my initial question about  
whether Metazoa or Animalia is the best name for the clade left over  
when you remove the old "Protozoa" from the old "Animalia". Opinion  
seems to be divided. Names with typification go with the type, so you  
can use the same name for very different taxonomic concepts, provided  
only that the concept includes the type. Names without typification  
are trickier. If you prefer to use the name Metazoa, then you think  
that the name should change if the concept changes, but it doesn't  
have to be that way. There is good reason for arguing that since your  
Metazoa includes all the "typical" animals in the popular sense, we  
should still use the name Animalia for it, and so Protozoa were  
removed from Animalia when it was discovered that they [Protozoa]  
weren't in fact animals. It's a semantic issue, rather than a  
scientific one, but it does have implications for classification  
(which is a mixture of science and semantics)...

By the way, imagine the uproar at a strictly cladistic  
reclassification of Animalia (or Metazoa) if it does turn out that the  
sister taxon to Eumetazoa is just some subclade of calcareous sponges!


Quoting Kenneth Kinman <kennethkinman at webtv.net>:

> Stephen,
>       Kingdom Metazoa = Phylum Porifera (sponges) + Eumetazoa (all the
> other phyla).  The only question these days is whether the sister group
> of Eumetazoa is all of crown group Porifera or some subclade thereof.
> Many researchers believe the latter, and that Eumetazoa evolved
> specifically from the calcareous sponges, which would make the crown
> group Porifera definitely paraphyletic (and even the crown group
> calcareous sponges could easily be paraphyletic as well).
>        The sponges themselves almost certainly evolved from
> choanoflagellates, making the latter paraphyletic (as well as the
> Protozoa as a whole).  The names are thus perfect reflections of what
> they are evolutionarily.  Protozoa means "first animals", and their
> descendants Metazoa ("higher animals").  Makes perfect sense to me.
>      Animalia (in the sense of Protozoa + Metazoa; first animals +
> higher animals) is also paraphyletic with respect to the photosynthetic
> protists when they acquired plastids.  Metazoa on the other hand is a
> clade, unless you believe those old theories that Porifera evolved from
> choanoflagellates, and Eumetazoa evolved from some other group of
> Protozoa.
>        ----------Ken
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