[Taxacom] 2 genera of Placozoa is not enough

Kenneth Kinman kinman at hotmail.com
Tue Aug 7 22:05:44 CDT 2018


Hi Stephen and Tony,

       I think it is about time that the diversity of placozoans is reflected in their formal taxonomy.  And recognizing a second genus is just a very conservative first step.   We could very soon see the new genus Hoilungia further split into separate genera, and even making Hoilungia the type genus of a new family separate from a Family Trichoplacidae (sensu stricto).

       As early as Voigt et al. 2004 ("Placozoa--no longer a phylum of one"; https://www.sciencedirect.com/science/article/pii/S0960982204008413 ) it was stated that "With SSU, for example, the genetic distances between individual placozoans are comparable to those documented between genera (within families) and even between families (within orders) of other diploblastic, early diverging metazoan phyla."

                    -------------Ken

P.S.  An expanded taxonomy of placozoans would probably encourage more collecting and studying of these organisms before their sensitivity to increased ocean temperature and acidity causes many taxa to become extinct before they can be collected.  Funding such research has to be governmental, because you are never going to even get many conservationists interested in such organisms (compared with concerns for vertebrate species facing declines or extinction).  They look too much like a common amoeba to elicit much concern from conservationists, much less the public at large.  However, their evolutionary importance to the early evolution of metazoans is huge, and their exact relationship with other primitive animal phyla is still very controversial.

________________________________
From: Taxacom <taxacom-bounces at mailman.nhm.ku.edu> on behalf of Tony Rees <tonyrees49 at gmail.com>
Sent: Sunday, August 5, 2018 5:35 PM
To: Stephen Thorpe
Cc: taxacom
Subject: Re: [Taxacom] Now 2 species/genera in Placozoa...

Hi Stephen,

>From my (limited) comprehension of the molecular data, the 2 presently
described species are just representatives of 2 very distinct molecular
groupings, see diagram at
http://journals.plos.org/plosbiology/article/figure?id=10.1371/journal.pbio.2005359.g003
[http://journals.plos.org/plosbiology/article/figure/image?id=10.1371/journal.pbio.2005359.g004&size=inline]<http://journals.plos.org/plosbiology/article/figure?id=10.1371/journal.pbio.2005359.g003>

Comparative genomics and the nature of placozoan species<http://journals.plos.org/plosbiology/article/figure?id=10.1371/journal.pbio.2005359.g003>
journals.plos.org
Author summary Placozoans are a phylum of tiny (approximately 1 mm) marine animals that are found worldwide in temperate and tropical waters. They are characterized by morphological simplicity, with only a handful of cell types, no neurons, no tissue organization, and even no axial polarity. Since the original description of Trichoplax adhaerens 135 years ago, no additional accepted species has been established, leaving the Placozoa as the only animal phylum with only a single formally described species. While classical morphological species identification has failed to reveal further species, single-gene DNA sequence analyses have identified a broad and deep genetic diversity within the Placozoa. To address the significance of this deep genetic diversity in this morphologically uniform phylum, and to better understand its consequences for speciation processes, general biology, and species delimitation in the Placozoa, we sequenced the genome of the placozoan isolate “H13,” a lineage distantly genetically




On a purely hypothetical basis, I do not see why a newly described species
could not be placed in its own genus or any other desired higher taxon
(even kingdom), if that is used as a proxy for its claimed morphological or
genetic distinctiveness.

Regards - Tony

Tony Rees, New South Wales, Australia
https://about.me/TonyRees


On Mon, 6 Aug 2018 at 08:22, Stephen Thorpe <stephen_thorpe at yahoo.co.nz>
wrote:

> I don't agree with putting the new species in a new genus! Genera cannot
> be correlated consistently with degree or "depth" of divergence, and really
> only serve to separate convenient monophyletic groups, but there is no gain
> in separating two species into two separate genera.
>
> Stephen
>
> --------------------------------------------
> On Mon, 6/8/18, Tony Rees <tonyrees49 at gmail.com> wrote:
>
>  Subject: [Taxacom] Now 2 species/genera in Placozoa...
>  To: "taxacom" <taxacom at mailman.nhm.ku.edu>
>  Received: Monday, 6 August, 2018, 10:09 AM
>
>  In case anypne interested missed it, there
>  are now 2 described
>  species/genera in Placozoa, doubling
>  the size of that curious phylum:
>
>
> http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.2005359
>
>  They still all look the same,
>  apparently, but that's another issue.
>
>  Regards - Tony
>
>  Tony Rees, New South Wales, Australia
>  https://about.me/TonyRees
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