Prosobranchia.

This is mainly untaxonomical group of mollusks that includes the snails which have well-developed gills and usually the shell. Prosobranchs have a famous anatomic feature: their shell is turned on 135-180° CW around the aperture. The ancestor's shell apex was directed ahead. The prosobranch's shell apex is directed back or to the left back.

The most of the marine shells belong to the prosobranchs except one very big group, nudibranchs. The nudibranchs and a few little known groups more belong to the Opistobranchia.

This is a very numerous mollusk which may go out from the water, Littorina littorea.

Cryptonatica clausii - a very interesting snail. Its foot is able to accumulate water, notice the big size of the foot! When the danger comes, the foot releases the water and draws into the shell.

On the third photo are the cryptonatica eggs.

Neptunea despecta, the biggest snail in the White sea. It may reach 12 cm in length.

Testudinalia tesselata - the limpet. The shell of this snail is adapted to the life in the surf zone.

The teeth af the limpet's radula.

Puncturela noachina. This snail is thought to be a primitive prosobranch because of the hole on the apex.

There are some shell-less prosobranchs in the White sea - the sea angels.

Clione limacina. These plankton organisms which foot was transformed to the wings feed only on the sea butterflies Limacina helicina.

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