Posted: Dec 29 2008
Stramonita rustica (Lamarck, 1822), Rustic Rock Shell
Update: Aug 2011
Ref: Claremont, M., Williams, S. T., Barraclough, T. G., and Reid, D. G. 2011. The geographic scale of speciation in a marine snail with high dispersal potential. Journal of Biogeography U. Biogeogr. 38: 1016-1032.
Referenced paper utilized the Stramonita haemastoma complex of shells to investigate the geographic scale of speciation in a marine snail with a long open ocean larval stage. Although not specifically focused on a comprehensive analysis to ascertain morphological and genetic speciation within the complex, the study did utilize a combination of molecular and morphological methods to establish geographical ranges and reconstruct phylogenetic relationships. As a result, the authors found support for six species within the Stramonita haemastoma complex. Although S. rustica was validated as a species having a wide range, that range did not include Florida. The authors found that only S. canaliculata and S. floridana occurred in Florida. The authors also found very supportive morphological evidence that S. rustica displays a distinctive feature from the other five species within the Stramonita haemastoma complex – a white aperture.
This is the only photo I found that I believe is a true S. rustica. Photo is from the collection of Bruno Lafitte.
2/26/13 Don Swenson (Coral Cove Marine Mollusk Checklist) posted on LTS Forum:
Because of the operculum I cannot tell if the entire aperture of this specimen is white. I recently live collected 2 Stramonita at Coral Cove. On one the interior portion of the aperture is yellow; on the other it is white. The outer lip of each is pale purple. Until I happened upon your article concerning Stramonita haemastoma & rustica, I assumed both were rustica. Your opinion?
Marlo (2/26/13): I go with David Reid until further molecular analysis demonstrates otherwise. S. rustica does not occur in Florida. I had sent David numerous Palm Beach specimens of what we had believed were S. rustica that were included in his study. Immature and beach shells of S. canaliculata and S. floridana may have all white aperture interiors. Since you beach collect, it would be quite helpful if you would indicate whether the shells you report were with the animal still present, whole shells or fragments, juvenile or adult. While including a fragment in a checklist is valid, fragments could well have been swept great distances by currents, tides, storms, etc. over many months from their "living habitat." For example, you have T. taurina on your Coral Cove list, but this single find was only a "worn fragment." If it had been a whole shell in reasonably fresh condition (or esp. if the animal was still present), we could infer that a living population might exist offshore in reasonably close proximity. However, a "worn fragment" could have come from a very distant origin, especially knowing about the powerful south-to-north Gulf stream flowing past Coral Cove and the very, very powerful tidal outflows through Palm Beach Inlet from Lake Worth just a few miles south of Coral Cove. Had I known your shell was only a "worn fragment," I would not have included it in my range data. I am far more conservative than Harry and generally give location credence only to whole beach shells (one valve of a bivalve) when inferring a proximate living population. A single worn fragment is not enough.