Fwd: Re: [Annelida] metamerism

Geoff Read via annelida%40net.bio.net (by g.read from niwa.co.nz)
Tue Nov 11 14:04:38 EST 2008


>>> On 11/11/2008 at 9:35 p.m., ADRIANA GIANGRANDE <gianadri from ilenic.unile.it>
wrote:

I do not agree with the below definitions. In all the text book of zoology
it is reported the opposite, Metamerism is a feature typical of Annelida,
Arthropoda and Vertebratas and its definition can be:
body plan in which two or more tissues or organs systems
> are organized metamerically along the A-P axis of the animal; metamers
> of different systems have the same repeat length. I should add: metamerism has
an embryological origin.
> Flatworm proglottids are segments and are originated by asexual reproduction,
im this way they also differ from segmentation present in other groups.  Whith in
nematoda I know only the presence of a segmented cuticle, and in monoplacophora
molluscs segmentation could be a true metamerisms!
 
It is not so easy! However I think is better to leave the term metamerism as
basical and in some cases segmentation could be used as synonym of
metamerism.

Best Adriana Giangrande

> Geoff is right that metamerism and segmentation are often used
> synonymously. But since there are two nice distinct words, they can also
> be used to distingush different degrees of regularity in body
> organization as follows:
> 
> Segmentation: body plan in which two or more tissues or organs systems
> (such as nervous, muscular, excretory, circulatory and/or integumental)
> are organized metamerically along the A-P axis of the animal; metamers
> of different systems have the same repeat length.
> 
> Metamerism: body plan organization featuring repeating units along the
> A-P axis but falling short of the rigorous definition of segmentation,
> e.g., only one organ system is arranged into repeating subunits, or the
> spatial repeat lengths are different between systems.
> 
> With this set of definitions, one can perhaps distinguish metamerism
> (in  flatworm, molluscs, nematodes) from segmentation (in most annelids,
> arthropods and vertebrates).
> 
> Best,
> David Weisblat
> 
> Geoff Read wrote:
>>>>> On 5/09/2020 at 4:59 p.m., "anil sharma" <asanilsharma3 from gmail.com>
>>>>>         
>> wrote:
>>   
>>> Give me details about metamerism in annelids
>>>     
>> 
>> Simply a term for a segmented body.
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