The snails in this enclosure (saltmarsh periwinkles, Littoraria irrorata) have found a blob of mycelium of Phaeosphaeria spartinicola, one of the major decomposers of blades of smooth cordgrass (Spartina alterniflora). The mycelium was grown in aqueous extract of senescent leaf blades of smooth cordgrass, harvested, and offered to the snails as potential food. After finding a fungal food source like this one, the snails will devour it completely. You may be able to see that the snail at the top is drawing a "spaghetti" of mycelium into its mouth. The snails assimilate 50% of the fungal food ingested, and can grow on a diet of it (though not as fast as they do when fed the whole, natural, decaying-leaf system). See Bärlocher & Newell, 1994, Growth of the salt marsh periwinkle Littoraria irrorata on fungal and cordgrass diets, Mar Biol 118:109-114.