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Date: | Thu, 2 Oct 2003 10:08:13 -0500 |
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Harry, Andy and others,
As usual Harry has been right on with his remarks on the etheriids
(except the explorers name was Burton not Barton. A personal hero of
mine......along with Harry of course). Not having seen them in situ
I really have no feel for how large the colonies are and how they
might fair as fare for a large South American catfish. I'm guessing
that once they grew to a reasonable size the cats might look
elsewhere for a meal. When you observed them in the Nile did they
occur in large colonies?
Kevin
>Date: Wed, 1 Oct 2003 19:39:11 -0400
>From: "Harry G. Lee" <[log in to unmask]>
>Subject: Re: freshwater oysters?- Tanzania
>
>Dear Andy and other inquiring minds,
>
>First - welcome back Rock-man Andy. We missed your nuggets for too long.
>
>The shells of the etheriids I know all have the same general floor plan as
>do the naiads from eastern North America. The outer shell layer is covered
>with a tenacious horny periostracum, which insulates it from the corrosive
>effects of acidic milieux and the abrasion of coarse substrata.
>
>There are several (infaunal) naiads with shells thicker than the etheriids
>I know; some with the burrowing habit are far thinner than these "oysters."
>
>I think it would take a robust catfish or terrapin to take on an
>etheriid. Maybe the sessile habit (vs. the infaunal posture) is protective
>against most important vertebrate predators in tropical Africa and South
>America (where other etheriid genera live)?
>
>Harry
>
>At 10:23 AM 10/1/2003, you wrote:
>>Harry Lee wrote,
>> > These are etheriids [Type genus Etheria Lamarck, 1807]. They are
> > usually placed in the Muteloidea, members of which are, like those of the
>> kindred superfamily Unionoidea, distinguished from all other extant
>> pelecypods in possessing a larval stage (lasidium for muteloids;
>> glochidium for unionoids) that is parasitic on a vertebrate, usually
>> fish, host. The "oyster" habit is a derived character. Its ancestral
>> forms were, like most pearly freshwater mussels, burrowers (infaunal as
>> opposed to epifaunal).
>>
>>How interesting. It must cost a great deal of metabolic energy to produce
>>such a thick shell in a freshwater environment. Is the shell protected by
>>a periostracum? Are the etheriids protecting themselves from acidic water
>>or from predators? What kinds of predators eat these bivalves?
>>
>>Nice to exchange words again. I notice that several people have rejoined
>>Conch-L at about the same time. Good news!
>>
>>Cheers,
>>Andy
>>
>>Andrew K. Rindsberg
> >Geological Survey of Alabama
>
--
Kevin S. Cummings
Illinois Natural History Survey
607 E. Peabody Drive
Champaign, IL 61820
[log in to unmask]
http://www.inhs.uiuc.edu/cbd/collections/mollusk.html
The Mussel Database Project
http://clade.acnatsci.org/mussel/
Join the Freshwater Mollusk Conservation Society Today!
http://ellipse.inhs.uiuc.edu/fmcs/
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