The boats which collect these shells belong to La Trinité harbour, on the northern side of Quiberon bay. They dredge wild Crassostrea gigas (see A. opercularis pages) at depths between 5 & 15m, on a mixture of sand, mud, gravel, little stones, and dead shells.

The Top-ten list of the species collected here is very representative of a rich filtering community in turbid and sheltered waters:

Cerastoderma edule (Linnaeus, 1758)
Laevicardium crassum (Gmelin, 1791)
Acanthocardia tuberculata (Linnaeus, 1758)
Mytilus edulis Linnaeus, 1758
Modiolus adriaticus Lamarck, 1819
Modiolus modiolus (Linnaeus, 1758)
Modiolus barbatus (Linnaeus, 1758)
Crassostrea gigas (Thunberg, 1793)
Aequipecten opercularis (Linnaeus, 1758)
Mimachlamys varia (Linneus, 1758)

uncommon
rare
rare
common
rare
uncommon
uncommon
abundant
uncommon
uncommon

...Without forgetting the inevitable Anomia ephippium & Crepidula fornicata.

Some other characters of this community are, of course, the Brittlestars (competition), Seastars (predation), sponges (association), soft corals, hydroids etc. Thus, to summarize, filter feeders and shell eaters in a beautiful balance... and Urchins.

The depth in this part of the gulf does not exceed the 20m (in the southern limit), most of the area being at 10-12m under the low tide level. North-east receives three rivers an a lot of small brooks.

The "Black Scallop", which is named "atra" by Locard, is the commonest form encountered in the bay.
It represents around 50% of the adult varia in this area. The interior is particulary impressive, with velvet reflections near the umbos (not clearly rendered on the pics).

The remainder of the population is mainly brown, mottled of light cream and dark spots. This is the average varia, which represents here only 40% of the shells. All the shell have well developped spines on their ribs, offering to many organisms an excellent anchoring, while the Crepidulas cannot cling.