Phylum: Mollusca

Class: Gastropoda

Subclass: Prosobranchia

Infraclass: Caenogastropoda

Order: Mesogastropoda

Family: Littorinidae

Scientific name: Littorina fabalis

 

Norwegian: butt strandsnegl

(Storsteinan - The Trondheim Fjord / 1 meters / 08.16.2001)

Distribution: Both species of flat periwinkles are common in the intertidal zone, especially on rocky shores, along the entire Norwegian coast. L. fabalis, also known as L. mariae, tends to live lower on the shore than L. obtusata, but this is not a strict rule, they do mix in the same locations.

 

Characteristics: The two species of flat periwinkle are easily confused. The picture to the left (from "Handbook of the Marine Fauna of North-West Europe")illustrates that they are best distinguished by the shape of the penis and the size and shape of the shell. However, studies in the Trondheim fjord indicate that shell shape varies so much that even specialists find it difficult to make positive identifications from the shell alone. It is reported from Sweden that the L. fabalis usually have a yellow body while the body color of L. obtusata is often black. Other observations indicate that body color tends to follow the color of the shell, regardless of species. The most common shell colors are black, olive green, brown and yellow, but even red shells have been reported. L. fabalis is even more flattened than L. obtusata. The length of the L. fabalis rarely exceeds 12 mm.

 

All pictures: