Order: Pulmonata

Family: Camaenidae

Species: Caracolus marginella (Gmelin, 1791)

Locality:  Puerto Rico

English Name: None.

Image: Phil Poland, on 35mm slide converted by slide scanner.

C. marginella is a member of the land-dwelling pulmonate gastropods, an order which contains almost 50% of the world's mollusc species, although because of deforestation and habitat degradation and destruction, and the introduction of non-native species in many parts of the world (some of which are ravenous carnivores, such as the notorious Euglandina rosea (Ferrusac, 1821), while others simply out-compete native landsnails for food - like the infamous banana slugs which invaded Florida and California in recent years) many pulmantes will never be known to science before they become extinct.

The family Camaenidae is a large, colorful family with over 90 genera, living in tropical North and South America, S.E. Asia, and Austalasia. Genera include the ground-dwelling Pleurodonte of the Americas (which resemble flattened pyramids), the much-sought and famous Papuina from Melanisia (one of which is the "Green Snail", a lovely but endangered species from Papua New Guinea), and the button-shaped Obba from the Philippines. All lay their small, soft eggs in moist earth, and all are vegetarians, munching on leaves or leaf litter. (source: Compendium of Landsnails: Tucker Abbott, 1989)

C. marginella (Gmelin) (a "tree-snail"), is an excellent example of a species which exhibits both right-handed (dextral), and left-handed (sinistral*) coiling forms. At first glance, the two images in the photo seem to be mirror images of each other, but if you look more closely, you'll see that they are in fact 2 different specimens - one sinistral, one dextral! Just as most humans are right-handed, so are most molluscs, but in the mollusc world, there are very few species which have both left and right-handed forms - many of them are in the Camaenidae family, interestingly enough! The sinistral specimens do not seem to suffer any disadvantage in a right-handed world, and some species of land and fresh-water snails are entirely left-handed - few or no dextral individuals to be found!!

LINKS: MacCoil mollusc shell coiling visualization program by Richard Palmer http://www2.biology.ualberta.ca/palmer/progs/MacCoil/MacCoil.htm

An annotated list of sinistral &dextral reverse-coiled gastropod shells now in the Lee Collection: http://www.jaxshells.org/reverse.htm

*The words "dextral" and "sinistral" come from Latin, and reflect our superstitions regarding left-handedness (about 15% of our species are naturally left-handed, but many are forced to learn at a young age, to use their right hand for most things, in order to conform to the majority: nobody likes to be different!!): if a person is "dexterous", he or she is clever and talented with their hands, where as the word "sinister", which means bad or evil, was applied to left-handed people who had not switched, or been forced to mainly use their right hands - merely because they were different from the majority. Even today, many societies and insecure individuals regard people who are different from their own tribe, group, skin color, nationality or religion, to be evil or to be feared or disliked, just because they were born that way. (in the molluscan world, no such prejudice has been observed, by the way!)