Scientific name: Tritia obsoleta

Where to find them: Common on sandy and muddy quiet water bottoms, intertidal

Ecological role: deposit feeders, benthos

They are everywhere but maybe you have not noticed them. On the sandy bottoms of West Meadow Creek and especially on the quiet-water bars at low tide on the beach side you can find thousands of mudsnails, known to marine biologists as Tritia (formerly Ilyanassa) obsoleta. Adults are 2-3 cm long. They cruise about on their elegant little ciliated feet, swinging their siphons side to side, searching for a morsel of food.

Typically they use their radula, or tooth belt to scrape microorganisms and bits of organic matter from the sediment surface. But they just love a good carcass! Find a dead crab or rotting bits of seaweed and you will see them congregate, scraping away. Imagine their luck! Thus these abundant snails are crucial for the sand flat ecosystem as they process literally tons of organic matter, much like earthworms do in the soil on land.

In June, the snails, which have separate sexes, copulate and the females lay egg cases on hard surfaces, which can be rare on sandy beaches and sand flats. Those that are not eaten will soon hatch and the larvae then swim in the water column for a few weeks. They then find a suitable new sand flat, settle, and metamorphose into a juvenile snail. Most of the many thousands of larvae produced die and often a few years pass before a successful set of juveniles occurs.

In June 2001 I found a large breeding aggregation in West Meadow creek. Here is an aggregation with yellow egg cases, which were attached to rocks and even the red-beard sponge.

The snails have burrowing cycles, but these are poorly understood. Often one sees them burrow as the tide comes in, perhaps to avoid being swept away. But many are often burrowed in the sand even in quiet water, which has not been explained.

In the spring the snails are often found in breeding aggregations but in West Meadow Creek they are often in patches about 10-12 inches wide and nobody knows exactly why.

The snails have some enemies, which can be yours as well. They often are breeding grounds for several species of parasitic flatworms known as trematodes, which reproduce and feed upon the snails internal organs. These organisms chew away at the insides of the snails, often preferring the naughty bits. As a result, the snails may be unable to breed by the time they become sexually mature. Snails are in many cases riddled with parasites, and the worms have a planktonic dispersal stage, which seeks a vertebate host. Yes, YOU might be that very host and the swimmers might burrow into your skin, causing swimmers itch. In areas where infection rates are high, you can stand in the water at low tide and develop a nice itchy red ring around your leg (actually, the last time West Meadow snails were tested the infection rates were rather low).

 

 

The eggs eventually hatch from the egg cases and swim for several weeks, eventually settling and transforming into juvenile snails on the mud flat, often in spectacular densities. This new dense population appeared near the Ernst Center in August 2022. Each snail is less than 2 mm long.