Flat periwinkle

Differences between the specie

It can apppear difficult to discern the differences between the two specie of flat periwinkle, but in reality it is quite easy:

Littorina fabalis is smaller; usually has a yellow body; a lemon-yellow or light brown shell; the shell spire is usually absent; and is common on bladder and toothed wrack.

Littorina obtusata is larger; usually has a black body; the shell is usually olive-green, dark brown or light yellow; a large whorl above the shell aperture is quite common; and is commonly found on knotted wrack.
    Both specie can be discerned by the appearance of their genitalia that is concealed by the shell. It is Littorina fabalis that is portrayed on the first page, in the upper left hand corner, aswell as on the next page. Littorina obtusata is pictured above.

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Differences between the specie

Eggs in jelly

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Bo Johannesson | Martin Larsvik | Lars-Ove Loo | Helena Samuelsson