Endozoic algae in shelled gastropods — a new symbiotic association in coral reefs?

Live algae were found in the hepatopancreas and gonads of the Red Sea snail Strombus tricornis. These organs are constantly concealed within the upper whorls of the snail's shell. Light penetration was 5–15% of the incident light reaching the shell. Pigment analysis indicated the presence of chlorophyll a, c and peridinin, a composition resembling the Dinoflagellata. Chlorophyll a concentration in the algae was 1.18±0.36 pg chl/cell. ¹⁴C assimilation of isolated algae incubated in the light exceeded that of dark controls, demonstrating the photosynthetic activity of the endozoic algae.