[Coral-List] Thinking like a coral (or jellyfish)?

[Herman Wirshing]

The discussion of the origins of the bilaterian body plan reminded me  
of this paper (see below).  I believe the paradigm is towards  
cnidarians containing an, at least, ancestral bilateral body plan.   
Included is the paper's conclusion.  More recent findings, however,   
may point in other directions.
- Herman Wirshing

Martindale MQ, Finnerty JR, Henry JQ (2002) The Radiata and the  
evolutionary origins of the bilaterian body plan. Molecular  
Phylogenetics and Evolution 24, 358-365.

Conclusions
The data reviewed here suggest that cnidarians, and
perhaps ctenophores, should be regarded as primitively
bilaterally symmetrical animals and that bilateral symmetry
might have evolved prior to origins of the Bilateria.
Bilateral symmetry, therefore, should not be
regarded as a defining feature (shared derived character
state) of the Bilateria. If bilateral symmetry is truly
homologous among Radiata and Bilateria, then dorsal–
ventral polarity is likely to be a homologous trait as
well. Bilateral symmetry requires polarity along an axis
through the single plane of mirror symmetry. A crosssection
through a bilaterally symmetrical anthozoan (a
hexacoral) reveals such axial polarity. This axis of polarity
might be homologous to the dorsal–ventral axis
of Bilateria. We are currently looking for molecular
and morphological indications of dorso–ventral polarity
during the development of both ctenophores and
cnidarians to determine whether all eumetazoans were
once built on a bilaterally symmetrical platform. The
presence of definitive mesoderm may also fail to distinguish
the Bilateria from the Radiata. If the muscle
cells of ctenophores constitute a mesodermal derivative,
then triploblasty is not a defining feature of the Bilateria.
Only one major morphological character remains
as an unambiguous defining trait of the Bilateria: the
coelom. If acoel flatworms are derived platyhelminthes
(and not basal triploblasts, Ruiz-Trillo et al., 1999),
then the possession of a coelom can be regarded as the
primitive condition for the Bilateria. Neither cnidarians
nor ctenophores display a coelom at any stage of
development.



>
>
> ------------------------------
>
> Message: 4
> Date: Wed, 24 Sep 2008 07:57:21 -0400
> From: Thomas Goreau <goreau at bestweb.net>
> Subject: Re: [Coral-List] Thinking like a coral (or jellyfish)?
> To: "Szmant, Alina" <szmanta at uncw.edu>
> Cc: coral-list coral-list <coral-list at coral.aoml.noaa.gov>,	Gene Shinn
> 	<eshinn at marine.usf.edu>
> Message-ID: <1B55D008-E985-4E5B-879B-DC241C6D9EA3 at bestweb.net>
> Content-Type: text/plain;	charset=US-ASCII;	format=flowed;	delsp=yes
>
> Dear Alina,
>
> I think even those that show six tentacles externally at the same time
> have gone through an earlier embryonic formation of mesenteries that
> follows a bilateral pattern around the directive mesentery.
>
> Best wishes,
> Tom
>
>
> On Sep 24, 2008, at 7:45 AM, Szmant, Alina wrote:
>
>> Hi Tom:
>>
>> Not sure I agree with your statements.  We are studying coral larvae
>> and settlement/polyp formation.  They are very much radial during
>> larval stage (planulae vs a pluteus or megalops for example), and
>> when they start to form the polyp, all six tentacle buds appear at
>> once.  Not sure about the internal septal formation because that
>> comes very late in Acropora.  They have solid planulae until they
>> morph into early polypoid forms.  In any case, corals don't have any
>> central nervous system, and as far as I kow only a neural net, so
>> they do not have radial thinking which is what Gene would be after.
>>
>> Regards,
>>
>> Alina
>>
>>
>>
>> *******************************************************************
>> Dr. Alina M. Szmant
>> Coral Reef Research Group
>> UNCW-Center for Marine Science
>> 5600 Marvin K. Moss Ln
>> Wilmington NC 28409
>> Tel: (910)962-2362 & Fax:  (910)962-2410
>> Cell:  (910)200-3913
>> email:  szmanta at uncw.edu
>> Web Page:  http://people.uncw.edu/szmanta
>> ******************************************************************
>>
>> ________________________________
>>
>> From: coral-list-bounces at coral.aoml.noaa.gov on behalf of Thomas
>> Goreau
>> Sent: Tue 9/23/2008 9:29 PM
>> To: Gene Shinn
>> Cc: coral-list coral-list
>> Subject: [Coral-List] Thinking like a coral (or jellyfish)?
>>
>>
>>
>> Dear Gene,
>>
>> Jellyfish, or corals or all coelenterates are not really radially
>> symmetric but bilateral, as is known to all coral anatomists and
>> embrologists. If you look at their embryonic development there first
>> forms a primary mesentery, (or septa) around which the rest are
>> inserted in cycles in which the position and sizes differ. It is
>> therefore a pseudo-sixfold symmetry that retains the primary  
>> bilateral
>> symmetry. Corals have basically the same set of genes for segment
>> formation as the higher invertebrates.
>>
>> So it is not clear that thinking like a jellyfish will prevent you
>> being bipolar, even though I agree with you multipolarity would be
>> very much better..........
>>
>> Best wishes,
>> Tom
>>
>> Thomas J. Goreau, PhD
>> President, Global Coral Reef Alliance
>> Coordinator, United Nations Commission on Sustainable Development
>> Partnership in New Technologies for Small Island Developing States
>> 37 Pleasant Street, Cambridge MA 02139
>> 617-864-4226
>> goreau at bestweb.net
>> http://www.globalcoral.org <http://www.globalcoral.org/>
>>
>> *********

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Herman H. Wirshing
Marine Biology and Fisheries
Rosenstiel School of Marine and Atmospheric Science
University of Miami
4600 Rickenbacker Cswy.
Miami, FL 33149, USA

Tel: (305) 421-4357 (office)
Email: hwirshing at rsmas.miami.edu