Regarding the apparently shrinking cones, several people mentioned temperature, and Paul M. has even provided data on how temperature can affect the size of cone shells. The temperature difference should also affect the measuring device. Different materials respond to temperature by expanding or contracting at different rates. If your measuring device were made of calcium carbonate, it should expand or contract at the same rate as the calcium carbonate cone snails (for the nit pickers, this equivalence is approximate since the cone shell also contains organic compounds and different crystal structures of calcium carbonate exist), and your apparent measurements wouldn't change. However, I have never heard of a calcium carbonate measuring device, so your ruler or caliper will likely expand and contract at a different rate than the cones. I believe that plastic is affected by temperature to a greater extent than metal, so a plastic caliper in the cold depths would shrink more and make the cones appear slightly larger, and the same plastic caliper in a warmer place would expand faster and make the cones appear slightly smaller. In any case, if your measurements are precise, the relative sizes of the cone snails should stay the same (i.e., the largest will still be the largest). Words of advice for repeatable measurements include (1) use the same measuring device, (2) take measurements at a standard temperature (room temperature or 20 C is a common standard), and (3) use a measuring device made of a material that changes size slowly with temperature (has a low coefficient of thermal expansion).
Timothy A. Pearce, Ph.D., Asst. Curator & Head, Section of Mollusks
Carnegie Museum of Natural History
4400 Forbes Ave, Pittsburgh, PA 15213-4080, USA
ph 412-622-1916; fax 412-622-8837; [log in to unmask]
www.carnegiemnh.org/mollusks/index.htm
"The views, opinions, and judgments expressed in this message are solely those of the author. The message contents have not been reviewed or approved by Carnegie Museums of Pittsburgh."
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