Have you ever waded in a narrow salt-water creek, or the waters of a marsh, or a calm and enclosed bay, and observed thousands of small black snails crawling about the muddy bottom? These tiny interesting creatures are the mud snails (Ilyanassa obsoleta) which are common marine scavengers around the Cape’s coastline.
To early investigators the snails appeared to be moving along on their stomachs, so they were classified as gastropods from the Greek work which means “stomach-footed.” The snails don’t really move on their stomachs. Like other organisms, their stomach is an internal organ which is enclosed in a mantle.
The morphology of the mud snail is a perfect example of a precise evolutionary adaptation. The snail’s shell is light enough to be carried around, and serves as a shelter for the fragile animal and as protection from hungry predators. On the back end of the foot exists a structure called an operculum. This flat shield-like structure plugs up the opening of the shell, thus protecting the animal from desiccation at low tide. The operculum grows at the same rate the shell grows. This structure is unique to marine snails.
Mud snails are plentiful in number on Cape Cod and serve an important ecological role in the marine community. The snails help break down dead organic matter which returns to the salt water environment in the form of needed nutrients. The snail detects dead fish by its sensitive tentacles, and then slowly heads towards the dead food source. Many snails will be attracted to the same food. They extend a long snout known as a proboscis which contains at its tip many rows of sharp teeth, a structure called a radula. By moving the radula back and forth, the snail scrapes its food in small portions. The entire process is slow, but effective as nothing is wasted.
In the complicated food web of a coastal ecosystem no activity can really be considered unimportant or insignificant, for even something as small as a snail may be a major component of that system.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.