I posted notice of my presentations of C. contracta and C. dietziana on Conch-L and received the following comments about these difficult species. My personal opinion is that Say's description of C. contracta based upon only two specimens from the same geographic population is probably not reflective of the variability present in this taxon. However, it is apparent that these two are distinct species if only based upon anecdotal evidence that the unique adult stage of C. dietziana has not been reported where large populations of C. contracta have been found. My research (and library) is limited and we can only expand our insight if a large sample of C. contracta material from diverse locations can be comparatively presented with further confirmation that adult C. dietziana were not found in the same location.

David Kirsh:

"Bravo for taking these on, Marlo! I know you had been reluctant to tackle Corbulas several years ago. I believe C. contracta is the common species in the genus in North Carolina. The members of this genus are difficult to distinguish in my estimation."

steve rosenthal:

"I have dietziana from Jim Moore dredgings 95 Miles off Egmont Key, FL in the Gulf of Mexico.

re C contracta: As noted in the Long Island Shell Club's Seashells
of Long Island (1988) recent local records were few and far between, and always in small numbers. Subsequently we found a beach in Suffolk County (Cedar Beach County Park, Southold, Peconic Bay) where we can find large numbers consistently every time we visited in the fall (during scallop season). Of the hundreds I got, the largest was 11.9mm. they were almost always restricted to an upper driftline where they tended to wind up under rocks and gravel.... I have Suffolk County shells from nearby Greenport, and North Haven; and one very lucky find of a pair and single valve from Nassau County (bayside of Jones Beach State Park) from 2001, after rough weather."

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Susan J. Hewitt:

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To me, these rather handsome corbulas look rather like what is shown for Caryocorbula chittyana on page 386 of Mikkelsen & Bieler, 2008. Perhaps they could be that species?

They don't look much like the photo on that same page of Caryocorbula contracta, which has the posterior tip of the shell quite pointed and a little curled under, rather than high, blunt and wedge-shaped like the posterior end of these are.

On Sunday I am going to Steve Rosenthal's house, and will take a look at the shells that might be C. contracta that he found out on Long Island.

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Marlo:

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I agree with you and Harry and I have been discussing C. chittyana vs C. contracta a bit upon considering the Folly Beach shell, above, which I suggested might be the former after also reviewing M&B. I believe he feels M&B have poorly represented these two and that all the above shells are the latter. Harry (Lee, 2009. Marine Shells of Northeast Florida.) did not report C. chittyana, but did report C. contracta.  See discussion of C. chittyana.

I've yet to obtain samples of C. chittyana. So, I'm having great difficulty being able to make a good direct photo comparison that would illustrate the characters that would distinguish these two.