November, 2018

Globular Drop

The cute little globular drop (Helicina orbiculata) is an extremely common land snail in our area. It is most often seen during wet weather, crawling on low vegetation where it scours organic matter with its rasp-like radula, or "tongue." During dry weather, the snail estivates in its shell, sealing off the opening to retain moisture within. This species is more closely related to many marine snails than it is to other land dwellers, and is described as a tropical terrestrial operculate gastropod. Translation: it needs a warm climate, breathes air although it is not related to pulmonate snails that have lungs, and has an operculum (a lid to close off its shell). One of the most notable signs of the globular drop's distinction from our numerous other land snails is the location of its eyes. They are not at the tips of the cephalic tentacles but at the base. Another, not so obvious, difference is that the sexes are separate; most land snails are hermaphrodites.

This snail has an odd feature that is not yet understood. The edge of the shell opening varies among individuals, ranging from very thick with a sort of back fold to thin with no lip at all. One theory is that the mollusk can sequester calcium in this feature when conditions provide ample amounts of the mineral and then draw upon that store when it is needed during lean times.