Distribution of Conchocelis of Red Algae Bangia sp. in the Nacreous Layer of Akoya Pearl Oyster Pinctada fucata Shell

We found filamentous structures resembling conchocelis of red algae within the nacreous layer of the Akoya pearl oyster Pinctada fucata shell. Microscopic analyses revealed that these filamentous structures had an autofluorescence and varied in length, occasionally branched, and exhibited diameters ranging from 2 to 5 μm—consistent with previously reported sizes for Bangiales conchocelis. We extracted DNA from organic matrix sheets obtained by decalcifying the shell and performed PCR with primers targeting red algae from the family Bangiales to identify these structures. Sequencing analysis confirmed a 94% match with that of Bangia fuscopurpurea, establishing the presence of Bangia conchocelis within the shell. Conchocelis distributed predominantly near the anterior ear across all examined shells. In 3-year-old oysters, conchocelis filament densities reached approximately 250 filaments per 1 mm², with a broader distribution area than a 2-year-old oyster, where densities were lower, peaking at 35 filaments per 1 mm². Conchocelis distribution was consistent between the left and right shells of the identical oyster. These findings suggest that conchocelis density and distribution expand with oyster growth, providing insights into the age-related dynamics of conchocelis localization in Akoya pearl oyster shells.