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jfatherree
07/11/2002, 04:57 PM
Here are some comments about the Tridacnid identification article made by Julian Sprung, and my response:

... figure 3 and figure 4 … are Tridacna maxima, not T. crocea. They are easy to confuse in any case, and the shells of either can cross the boundaries of the others' defining characteristics. Tridacna maxima can have a very wide byssal opening and shortened shell, but it is always distinguished by protein layers forming a soft ring around the byssal opening, something T. crocea lacks. After having observed enough of these guys it is also possible in most cases to distinguish clams by mantle coloring. In the case of figure 3, I rely on both mantle color and shell shape.

The article is nevertheless very good and I really enjoy your magazine.

Sincerely,

Julian Sprung


… Admittedly, I've never heard or read about the protein ring that he (Julian) speaks of being used for positive identifications, but it is certainly present on some clams. I guess I've never paid attention to which ones though. I see in The Reef Aquarium that Julian/Charles say that "The edges of T. maxima's byssus opening tend also to curl upwards with a chitinous ring surrounding it." But, to me "tend" makes that a bit vague as to whether this feature is a positive identifier. The references are personal observation, and Achterkamp, 1987, which is in German, so I haven't read that one. I can't find any other mention of the ring being used as a positive identifier in anything else I have on the subject either. But of course, that doesn't mean it isn't true. So, I'll take Julian's word on the subject…

As far as the pictures go, obviously I didn't look for a ring on this specimen when I took the photos and identified the clam in person. The specimen was in a store's tank several years ago, so I can't go back and re-check either. I've gone back into my file cabinet to double-check though, and the slides say "crocea" on them, so at least at that point I was sure it was crocea. Now looking at just the two slides though, I can't convince myself that it has to be one or the other. One of the points of the article is the fact that it can be very difficult to make identification based on color/pattern, and I can't tell too much about this clam's shell from the just the photo either. So, without hands-on verification of a ring, and considering that there is no "side view", etc. of this specimen, I'd think it would be best to leave it as is …


JF