Dendostrea folium (Linnaeus, 1758)
Indo-W. Pacific, Red Sea to Central Mediterranean…
Original taxon: Ostrea folium. Many synonyms.
 
Previously known, in Mediterranean, from the Iskenderun area only, the species has now crossed the Corinth Canal. It lives attached on gorgonians, ropes, woods or other shells, from the surface down to at least the upper circalittoral.

This cluster was found attached to a rope, northwestern shore of Vouliagmeni marine lake, west of Perachora, Loutraki area, northeastern Korinthia, Greece, september 2017. 44mm.
Ostrea folium drawn in A. J. Dézallier d’Argenville: La Conchyliologie, tome 3, Paris 1780, via BHL.
 
« A West Indian shell ; introduced by Dr. Turton, as it had been taken alive on the bottom of a foreign vessel. The specimen in his cabinet is not the true crista-galli as he imagined, but a characteristic example of the long lost folium of Linnaeus. » – Forbes & Hanley: A history of British Mollusca and their shells, London 1853, via BHL.
1m deep, on a big rock off Agia Fotiá tavern, Agia Fotiní beach, Keramés coast, east of Préveli, S. Crete.
The hinge and the muscular prints in this specimen.
The chomata (expressed here by small bright white dots along the margins) are restricted to the hinge area in the left valve (top image), but extend to the ventral margin in the right valve (bottom image). Width about 3cm.
A specimen from the upper infralittoral, Saronic Gulf. 30,9mm.
Top: Ostraea affinis from Diego Garcia, and bottom: Ostraea dubia (« Hab. Formosa? ») in G. B. Sowerby II: Conchologia iconica vol. 18, London 1873, plates XXIX and XXXIII, via BHL. Both taxa are synonyms of folium Lin.
Moyade islet, western end of Riou Island, south of Marseilleveyre coast, Provence, S. France. Original picture provided by S. Le Bris for iNaturalist – (CC BY-NC).
The close species Dendostrea frons (Linnaeus, 1758): North Carolina to Caribbean, SW. Ireland & Cornwall, possibly also in equatorial W. Africa…. The records from eastern mediterranean may be due to confusion with folium. In fact, the morphological differences are anything but obvious. Above: a specimen pictured at Tent Bay, SW. coast of Saba Island, Caribbean Netherlands, by N. DeMaster for iNaturalist – (CC BY-NC).
Ostraea folium in Sowerby II, op. cit. plate XVII: « Central America, on roots of mangroves ».
Most probably Dendostrea frons.
Ostraea frons in Sowerby II, op. cit. plate XIX: « West Indies ».

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