Actually the molecular work on Geukensia was done partially by Taehwan Lee and Diarmaid Ó Foighil (below). They used Ischadium recurvum, Geukensia demissa, and G. granosissima as outgroups in molecular studies of species of Brachidontes. Both combined (28S and ITS1) nuclear ribosomal (left) and mitochondrial COI (right) datasets suggested to these authors that G. granosissima is more closely related to Ischadium recurvum than it is to G. demissa.  One of the possible interpretation of their results, from the taxonomic standpoint, is that Ischadium recurvum could be just another species of Geukensia.

Lee, T. and D. Ó Foighil. 2004. Hidden Floridian biodiversity: mitochondrial and nuclear gene trees reveal four cryptic species within the scorched mussel, Brachidontes exustus, species complex. Molecular Ecology 13, 3527–3542 (doi: 10.1111/j.1365-294X.2004.02337.x)

Lee, T. and Ó Foighil. 2005. PLACING THE FLORIDIAN MARINE GENETIC DISJUNCTION INTO A REGIONAL EVOLUTIONARY CONTEXT USING THE SCORCHED MUSSEL, BRACHIDONTES EXUSTUS, SPECIES COMPLEX. Evolution 59(10): 2139–2158

Cheers from Sanibel,

José
________________________________________________________
José H. Leal, Ph.D., Director and Curator
The Bailey-Matthews Shell Museum
Editor, The Nautilus
www.shellmuseum.org

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________________________________________
From: Conchologists List [mailto:[log in to unmask]] On Behalf Of Harry G. Lee
Sent: Tuesday, October 06, 2009 5:55 PM
To: [log in to unmask]
Subject: Re: [CONCH-L] Florida Geukensia

Listers,

I think "northern Florida" might be better expressed as "eastern Florida," but let's hear what the panhandlers have to say.

Harry

At 04:59 PM 10/6/2009, you wrote:

Mikkelsen & Bieler, 2008 Seashells of Southern Florida (Bivalves) - which is likely the current authority on the subject, says under G. granossissima: "Florida, Gulf of Mexico, Caribbean, Central America, South America (Venezuela)...Formerly known as demissa Dillwyn, 1817 (eastern Canada to northern Florida)...."

John
Lancaster, PA

At 02:19 PM 10/6/2009, you wrote:

G. granosissima has been treated as a subspecies of G. demissa, but more recently they've been treated as separate.  I was never sure and still am not.  However, I finally got my hands on some G. granosissima, did a little reading and corresponding and have concluded that the Geukensia on Florida's east coast (G. demissa) is morphologically different from the Geukensia on Florida's west coast (G. granosissima).  See http://z14.invisionfree.com/Conchologist_Forum/index.php?showtopic=1826 for photos.

I would certainly like to hear from anyone who has found these shells on either coast of Florida that contradict the geographic separation I have presented.  More photos of west coast Geukensia would also be appreciated.

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