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Posted: Dec 8 2010

 Anadara brasiliana (Lamarck, 1819), Incongruous Ark

Previously Scapharca (Anadara) brasiliana (Lamarck, 1819)

The above presentation was motivated by an inquiry made by Marcus Coltro of Brazil on Conch-L:

12/6/10 Subject: Anadara brasiliana in Texas

“Shells from Texas are quite different from the ones from Brazil and Venezuela.  Specimens from Texas seems to be more granulose, having wider valves and looks like their umbus never touch the other side. After the shell grows to a certain size both valves touch on the umbus, preventing the shell to open. It has to grind off the excess moving the valves sideways so it can be opened again - this produces a hole in both valves - as seen on the right specimen from Brazil. I guess since it lives on mud that hole would not put the shell at risk from predators.

Anyway, shells from Texas seems to be something else, not A. brasiliana. Has anyone studied this group? Maybe Say was right calling it Anadara incongrua (assuming the type is from this area).

I've never had any specimens from US East coast - what do they look like?"

Marlo offered:

“I have only two juvenile specimens from Georgia. But, Bill has several good photos at (look for Scapharca brasiliana).

I can photograph mine if you’d like.”

Marcus replied:

“Thanks Marlo

Indeed it (photos at jaxshells) looks quite different from what we call A. brasiliana.”

Harry Lee contributed:

“I think it is important to determine just what the species is.

The type locality for Arca brasiliana is Rio de Janeiro according to the original description (Lamarck, 1818: 44; species 33).

There is no type figure, and the type specimen(s)

was located exclusively in the collection of Jacques-

Louis-Marin Defrance (1758-1850). Fortunately that

collection eventually reached the Muséum National

d'Histoire Naturelle, Paris, and a probable syntype,

a right valve, was discovered, discussed, and figured

(Lamy, 1906: 308-309; Fig. 2).

In the discussion, Lamy makes the point that the

figured shell matches the description (to the mm),

and 'de cette espèce, telle que Je l'ai préecisée ici

même (J. de C., 1904, p. 162*).'

I think the shell can be considered at the very least

'authentic' if not a well-qualified contender for lectotype.

To me it looks like the R valve at ...

Does it differ from what you call Scapharca brasiliana

(Lamarck, 1818)?

Marcus replied:

“Jose is right now in the Museum of Natural History in Paris and I've just told him to try to take pictures of this specimen (if it can be found...) and more details from the label.

Our shells are not like that illustrated on the article, it looks more like Texan shells.

Reading the text (using my poor French) I see Dall had access to specimens from Texas looking like both A. brasiliana and A. incongrua - but where is the type of A. incongrua?”

Harry then added:

“Say (1822: 268) cited a specimen(s) in the ANSP and gave the type locality as "estuaries of the United States."

Paul Callomon might be able to answer your question, but not all Say's types can be accounted for.

Say, T., 1822. An account of some of the marine shells of the United States (cont'd) [part 2 of 3]. Journal of the Academy of Natural Sciences of Philadelphia 2: 257-276. "June" [July]."

Marlo's comment:

To me the shells from the USA Atlantic coast and Texas, but for the differing camera angles, look like very close matches to Lamarck's shell. The beading on the Texas shell appears greater than usual for a right valve, but certainly not something that would question its identity.

Harry:  In my 12/6/10 posting misstated the date of Lamarck's ("1818": 44; species 33) description and failed to provide the reference:

Lamarck,J. B.P.A. de M. de, 1819. Histoire naturelle des animaux sans vertèbres présentant les caractères généraux et particuliers de ces animaux, leur distribution, leurs classes, leur familles, leurs genres, et la citation des principales espèces qui s'y rapportent; précédée d'une introduction offrant la détermination des caractères essentiels de l'animal, sa distinction du végétal et des autres corps naturels; enfin l'exposition des principes fondamentaux de la zoologie. [Première édition] Tome 6 Partie 1. Lamarck, Paris. i-vi + 1-343. Feb. to June.

The year of publication is 1819 as Marlo has indicated throughout this discussion.

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