Tamiami bivalves help needed

[Plantguy]

Well so much for getting distracted again...Uggh! I need to pay attention..Anyways, I just realized I created an earlier thread for a gastropod that I was labeling as a bivalve.oops..I also do need help with actual bivalve IDs....both are from APAC spoils Sarasota County.  Possibly Beds 10 or 11 lower Tamiami formation. Thinking the first one is a Chama. Matrix removal has been a bear on these..

 

And the 2nd I was thinking it might be Marvacrassatella but thats just a guess. I'm going to consolidate the exterior hopefully this week and then separate the valves to get a look at the scar/hinge area if they can be separated. 

Thanks for any help/confirmation. 

Regards, Chris 

[FranzBernhard]

Thanks for sharing, nice bivs!

Sorry, but can not help, I am always at a loss with bivs myself...

Franz Bernhard

[Monica]

I think @MikeR will be able to help with identifications...

 

@Max-fossils is also a fan of bivalves... (I am, too, but I'm not good at identifications )

[Max-fossils]

Very nice shells!

The second one is probably Eucrassatella meridionalis. You were on the right lines  LINK

The first ones definitely look like Chama's, but which species I'm not so sure... I'm gonna take a guess and say the left one is Chama corticosa and the right one C. emmonsi.

 

Did you find these yourself?

 

[Max-fossils]

2 hours ago, Monica said:

@Max-fossils is also a fan of bivalves... (I am, too, but I'm not good at identifications )

Thanks for the tag; probably would've missed these beauties otherwise  

[MikeR]

Hi Chris

 

On the left is Chama conregata Conrad, 1833 found in all Southeastern US Upper Pliocene deposits from Virginia to South Florida.  The other is Eucrassatella meridionalis (Dall, 1900) also found in the Jackson Bluff Formation in the Florida panhandle.

 

Mike

[Max-fossils]

4 hours ago, MikeR said:

On the left is Chama conregata Conrad, 1833 found in all Southeastern US Upper Pliocene deposits from Virginia to South Florida.

Is this for both Chama shells or only for the left one?

[MikeR]

18 minutes ago, Max-fossils said:

Is this for both Chama shells or only for the left one?

 

For both.  One is an upper valve the other the lower.

[Max-fossils]

38 minutes ago, MikeR said:

 

For both.  One is an upper valve the other the lower.

Ok that makes sense, thanks.

Just for me to learn more: how can you tell the different Chama species apart? What is it (morphologically speaking) that made you say that these are C. conregata and not C. corticosa or C. emmonsi?

[MikeR]

On 9/30/2018 at 3:13 PM, Max-fossils said:

Ok that makes sense, thanks.

Just for me to learn more: how can you tell the different Chama species apart? What is it (morphologically speaking) that made you say that these are C. conregata and not C. corticosa or C. emmonsi?

 

Although all three have similar characteristics, once you know what to look for it can be quite easy to tell them apart.  The attached valve is the large valve of the two which attaches to a hard surface such as a rock or another shell.  If it bends clockwise (to the right) it is Chama congregata.  Both Chama corticosa and C. emmonsi bend counter-clockwise (to the left). C. emmonsi can be differentiated by its squarish shape and has an indentation along the lower margin of the shell.

 

  

[Plantguy]

You all are awesome! Thanks again for the comments/help and ID's and discussion...I need to go look at my other Chama's---didnt ever notice bend orientations---probably should have..gonna be neat to see a bunch of them next to each other...they were surface finds from years ago that are in different places/drawers at the moment. Good stuff---thank you. 

@FranzBernhard, @Monica, @Max-fossils, @MikeR

Regards, Chris 

[Max-fossils]

17 hours ago, MikeR said:

 

Although all three have similar characteristics, once you know what to look for it can be quite easy to tell them apart.  The attached valve is the large valve of the two which attaches to a hard surface such as a rock or another shell.  If it bends counter-clockwise (to the right) it is Chama congregata.  Both Chama corticosa and C. emmonsi bend clockwise (to the left). C. emmonsi can be differentiated by its squarish shape and has an indentation along the lower margin of the shell.

 

  

Thanks for the explanation, that's helpful! 

So the orientation of the shell can be a determining factor for the Chama, similarly to how sinistral/dextral shells are sometimes the main criteria in gastropods. Very interesting!

It's true that it's the kind of stuff you never think about, but once you know it it's so obvious. 

[MikeR]

2 hours ago, Max-fossils said:

Thanks for the explanation, that's helpful! 

So the orientation of the shell can be a determining factor for the Chama, similarly to how sinistral/dextral shells are sometimes the main criteria in gastropods. Very interesting!

It's true that it's the kind of stuff you never think about, but once you know it it's so obvious. 

Exactly.  Its encoded within the organism's DNA.

[KathyGrant]

So this one is C. congregata, correct? That's what I'd thought, but someone in another group told me it's C. corticosa, and proceeded to tell me exactly the opposite of what MikeR said above. Found at Chippokes Plantation beach in Surry, Va. (Yorktown formation). 2-3/8 inches = longest dimension. Thanks!

Edited January 3, 2022 by KathyGrant

[MikeR]

18 hours ago, KathyGrant said:

So this one is C. congregata, correct? That's what I'd thought, but someone in another group told me it's C. corticosa, and proceeded to tell me exactly the opposite of what MikeR said above. Found at Chippokes Plantation beach in Surry, Va. (Yorktown formation). 2-3/8 inches = longest dimension. Thanks!

 

MikeR was wrong in the post above.  At that time in 2018, He read Campbell's descriptions and wrongly interpreted them for the post.  The large valve is called the attached valve as it attaches to a hard surface such as a rock or heavy dead shell while the small valve opens to allow the animal to filter feed.  As described by Campbell (1993):

 

76. Chama congregata Conrad" I833 (Synonym:" Crepidula
species" Jasper Burns, f 99 I ). Shell small to medium in size;
unattached right valve oval to circular in outline with low
axial corrugations and, in some specimens, a few short flat
spines. Fine crenulations on the inner margins of the valves.
Attached left valve coiled clockwise. Zone 1. Williamsburg;
Middlesex County; Zone 2. James City, Surry and Isle of
Wight counties, Petersburg, Williamsburg, Yorktown, Hampton,
Chuckatuck, Suffolk and Chesapeake Length 20 mm,
height 23 mm.
77. Chama corticosa Conrad, 1833 (Synonym: Chama
agassizii "Wagner" Dall, 1898). Shell large, massive,
subcircular, attached by the counterclockwise coiled right
valve. Juvenile and occasional adult specimens sculptured
with thin, ruffled lamellae; typical adults rough, irregular in
sculpture. Zone 2,Isle of Wight and James City counties,
Petersburg, Williamsburg, Yorktown and Suffolk. A common
host species for endolithic bivalves such as Lithophaga
and Gastrochaena. Length 44 mm, height 52 mm ; Spamer
and Forster (1988

 

At the time of the post, I looked from the top of the attached valves, however I should have looked at the coiling direction in the shell's living position,  Therefore based on Campbell's description, corticosa coils counterclockwise to the left.  I discovered the error a year after the my post as I was identifying Chama shells from both Virginia and Florida and forgot about my misstatements.  I still stand by my identification on your Facebook post in Fossil Bivalves as Chama corticosa.

 

Mike

Edited January 4, 2022 by MikeR

[KathyGrant]

Thanks for the clarification! I'm still confused, though. Whether you hold the shell the way it's pictured or flip it upside down, as it sounds it would be in life, the whorl curls clockwise. Or am I misunderstanding something?

 

 

Edited January 4, 2022 by KathyGrant

[MikeR]

1 hour ago, KathyGrant said:

Thanks for the clarification! I'm still confused, though. Whether you hold the shell the way it's pictured or flip it upside down, as it sounds it would be in life, the whorl curls clockwise. Or am I misunderstanding something?

 

Below is Chama corticosa from the type locality of the Upper Pliocene Rushmere Member of the Yorktown Formation in Isle of Wight County, Virginia.  In many cases the two valves of a bivalve are very similar such as burrowing ark and cockles shells, however those species which are exposed at the surface to feed such as oysters and Chama shells will have two unequal valves.  A bivalve's umbo (hinge region) terminates in the beak.  On the left is how the shell would be exposed if live, while on the right is the shell with the lower free valve removed.  Looking at the attached valve, you see that the umbo/beak curves counter-clockwise.

 

Edited January 4, 2022 by MikeR

[KathyGrant]

Thanks so much, Mike, for taking the time to explain. I really appreciate it. I'm an idiot. Lots for me to learn.

Edited January 5, 2022 by KathyGrant