Message 2001-06-0043: Lophotrochozoa

Tue, 01 May 2001 17:08:55 -0500

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Date: Tue, 01 May 2001 17:08:55 -0500
From: "David M. Hillis" <>
Subject: Lophotrochozoa

>     Lophotrochozoa is a perfect example of a group which should NOT be
>formally recognized.  It is almost certainly a broadly paraphyletic group that
>gave rise to the holophyletic Ecdysozoa grouping of phyla.  They are simply
>non-ecdysozoan bilateria, and the notion that they are the sister group to
>ecdysozoans is going to be very difficult to dispel.
>    These and other formal intermediate rank names (Coelomata, Protostomia,
>Uniramia, etc.) do more harm than good in determining how the various
>invertebrates are related to one another.  In my opinion, PhyloCode will only
>accelerate the generation of such problems.
>               -----Ken Kinman

1. Lophotrochozoa cannot be a paraphyletic group, because it was 
DEFINED as a monophyletic group (the last common ancestor of 
bryozoans, phoronids, brachiopods, annelids, and mollusks, and all 
the descendants of that common ancestor). This definition was written 
well before any draft of the PhyloCode.

2. The discovery and definition of Lophotrochozoa preceded the 
definition of Ecdysozoa, and even the paper that described Ecdysozoa 
supported its sister-group relationship to Lophotrochozoa.

3. I'm aware of no published evidence that supports your claim that 
Lophotrochozoa is not the sister-group of Ecdysozoa; perhaps that is 
why this will be a difficult notion to dispel. I'd be happy to 
reconsider my recognition of this clade (that is, synonymizing it 
with Bilateralia) if I'm presented with compelling evidence that 
these two taxa are synonyms. That is what science is all about.

4. Even if your premise is correct, and Lophotrochozoa is a synonym 
of Bilateralia, then it will be an easy matter to synonymize the 
former with the latter. If Lophotrochozoa had been named as a ranked 
taxon, then all the other nearby ranks among metazoans would have had 
to be changed, and then changed back  again if Lophotrochozoa is 
really found to be synonymous with Bilaterialia, as you suggest 
without supporting evidence. What a waste of everyone's time. This is 
actually a great example of why ranking, if it is done at all, should 
be completely separated from the task of discovering and naming 
higher taxa.

5. Naming Lophotrochozoa as an unranked clade allows us to focus on 
the science, rather than arbitrary decisions of rank. We can 
legitimately argue about whether Lophotropchozoa is the sister-group 
of Ecdysozoa or a synonym of Bilateralia, without arguing about what 
ranks may be assigned to these taxa. I find this much  more 
economical than arguing about whether bryozoans, phoronids, 
brachiopods, annelids, and mollusks form a monophyletic sister group 
to Ecdysozoa on one hand, versus the position that the clade that 
includes bryozoans, phoronids, brachiopods, annelids, and mollusks 
also includes Ecdysozoa on the other hand. For me, nomenclature is a 
tool for talking about the Tree of Life, and I don't want a system 
that restricts me to talking about a few arbitrary clades. The 
PhyloCode doesn't restrict you from ranking taxa if you want to, but 
it does free the rest of us to focus on the whole phylogeny of life.

6. Many of us care a great deal about the details of the Tree of 
Life, and I find your argument that we should be unconcerned about 
"intermediate rank" taxa insulting. You are basically saying that our 
interests are unimportant. I don't restrict you from ranking taxa if 
you want to do so; please don't restrict the rest of us from naming 
the things that we think are important (the parts of the Tree of 
Life), and please don't try to force us to use ranks that we find 
distracting, misleading, unnecessary, and cumbersome. I notice that 
you have no problem talking about the higher phylogeny of 
invertebrates without mentioning ranks...what would ranks add to this 

David Hillis

David M. Hillis
Director, School of Biological Sciences
Director's office: 512-232-3690 (FAX: 512-232-3699)
Alfred W. Roark Centennial Professor
Section of Integrative Biology
University of Texas
Austin, TX 78712
Research Office: 512-471-5792
Lab: 512-471-5661
FAX: 512-471-3878


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