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
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Champaign, IL 61820
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