Those specie of mud snails that are present
in Sweden are also found along the Atlantic coasts of Europe and Africa,
from Norway in the north to Senegal in the south. They are also present
in the Mediterranean.
Mud snails act as hosts for a great many
parasites. One of the many attackers are for example digenetic flukes
(Trematoda), which often go through several different stages of development.
Mud snails are usually infected when they eat the eggs whilst fouraging
for food on the bottom and thereby becaming hosts for the first stage
of development. The following stages usually infect birds and fish.
Flukes usually attack the reproductive organs of the periwinkles
so they cannot produce sperm or eggs. Even the hormone balance can be
disrupted, thus affecting growth so that they grow larger and quicker.
3 of 3