The Ponderous Ark, Eontia ponderosa (Say, 1822), is one of the most common shells found on the beaches of Sanibel and Captiva islands. One of the most striking features of this species is its dark-brown or black, velvet-like periostracum, the organic shell layer that covers part or the entire shell. Visiting beachgoers often confuse the periostracum of the Ponderous Ark for a layer of oil or tar that could have deposited on the white shell. Another feature that sets the Ponderous Ark apart from other local species of mollusks is its association with the false Sea Fan, Leptogorgia hebes Verrill, 1869, a marine colonial organism related to Sea Whips, Sea Anemones, and Corals. False Sea Fans attach themselves to the posterior region of Ponderous Arks, and may profit from an enhanced food supply (zooplankton) facilitated by the water currents created by the filter-feeding host bivalves. The photo on right shows a Ponderous Ark with attached colony of the False Sea Fan, Leptogorgia hebes.
Photos by José H. Leal.
[The scientific name of this species recently reverted to Noetia ponderosa.]