Posted: Sep 1 2007,
Pseudochama in FL no more, no more, Explanation of Pseudochama vs Chama
This discussion presents Chama and Pseudochama as distinguished by Abbott (1974). Current work has made this distinction obsolete.
Abbott identified only two
Pseudochama in Florida - P. radians
and P. inezae. The adjacent figure
illustrates the shell that for about
the last 85 years, and probably still
most often today, is referred to as
Pseudochama radians (Lamarck,
1819). In 1917 Odhner separated
the genus Chama into two genera
- Chama and Pseudochama. Among
the characters he relied upon to
distinguish the two were that Chama
attach by the left valve and
Pseudochama attach by the right
valve. However, technology,
research and knowledge march on,
and at the International Marine
Bivalve Workshop in Long Key,
Florida, July 2002, Campbell et al.*
[Campbell, M. R., Steiner, G.,
Campbell, L. D. and Dreyer, H., 2004.
Recent Chamidae (Bivalvia) From The Western Atlantic Ocean. Malacologia 46(2): 381-415] proposed two significant classification revisions for Florida Chamidae. Their studies, based upon morphological and DNA examinations, also found that P. inezae attached 50:50 by either the right or left valve, and that the prodissoconch of P. inezae was characteristic of the genus Chama. Their DNA analysis placed both in the genus Chama , with P. radians closely related to Chama congregata. Therefore, they reclassified both in the genus Chama. These two shells should now be identified as:
Chama radians Lamarck, 1819
Chama inezae (F. M. Bayer, 1943)
So, that leaves Pseudochama in Florida no more, no more.
Malacolog has adopted these generic name changes. Note that in doing so the reversion to Chama for radians necessitates the removal of parentheses from the author's name since Lamarck originally placed radians in the genus Chama. And, similarly, in reverse, since Bayer placed inezae in Pseudochama, parentheses have been added around Bayer's name. When a shell is reclassified from its original assignment, parentheses are added around the author's name and date of description.
*In their 2002 presentation paper Campbell et al. studied a lot of 16 specimens of C. inezae collected by Tom Honker off of Palm Beach County, Florida and found a 50:50 ratio of right valve and left valve attachment for C. inezae. They commented that “This is the first known example of this attachment pattern for a Recent species from the western Atlantic.” Harry Lee has pointed out to me in personal correspondence after reviewing this presentation that Campbell, et al. were apparently unaware that this same observation had previously been reported in 1970 by Robert C. Work of Miami in his article “Comments on Pseudochama inezae F. M. Bayer," Seafari (Palm Beach Co. Shell Club) 12(1): 1-2. Jan. Mr. Work reported that “Ten of 17 specimens were of the dextral ("Chama"-type) chirality, and only seven were of the sinistral ("Pseudochama") orientation.” A complete scanned copy of Mr. Work’s article follows. This copy includes Mr. Work’s edits after publication.