Ponderous Ark
Noetia ponderosa (Say, 1822) (previously Eontia ponderosa)
The Ponderous ark is a common shell found easily on S. Hutchinson Island beaches. Many versions still have the periostracum, black covering around the outside of the shell extending towards the beak.
Four Ponderous arks showing the periostracum (black covering) collected on S. Hutchinson Island December 2020
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The Ponderous Ark
José H. Leal, Oct 23, 2015
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.
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[Marine Life] The ponderous ark, Noetia ponderosa (Figure 3.31), has a heavier shell and is characterized by the lack of a byssus in the adult and the presence of a heavy periostracum. The siphons of these filter-feeders are greatly reduced, and thus, they are shallow burrowers.
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Ponderous Ark:
Thick and Heavy
By Patricia B. Mitchell.
This shell is very thick, and heavy for its size. It has distinct radiating ribs (usually around 30) and the rear margin of the bivalve slopes down from the hinge/beak area. The off-center, very prominent beak points toward the rear of the shell. The hinge has comb-like teeth which are visible along the length of the hinge line. The shell may reach a length of 2½ inches. (Looking at the inside of the shell, you will notice that the shape is trapezium-like.)
The ribs may exhibit a bold longitudinal groove (see further information on this “cut-ribbed” feature).
The shell washes up on beaches anywhere from Texas to Virginia and occasionally fossil specimens are found farther north. The non-fossilized specimens are often covered with a blackish-brown felt-like periostracum, though the beak may lack the dark covering.