The amber pen shell has a pair of long, thin translucent valves held together by ligaments that run along the entire dorsal side of the bivalve.

Algae (e.g. Lobophora variegata) and invertebrates such as sponges and encrusting corals tend to grow on the exposed part of the shell and may camouflage it very well.

The amber pen shell can be found in coastal western Atlantic waters, ranging from southern Florida across the Caribbean and the West Indies to Brazil.

Unique gutter-like waste canals in the viscera of the inhalent chamber also help to keep gills and other organs clear from silt and other unwanted water-borne particules by expelling these as pseudofeces.

Shrimp Pontonia mexicana (Palaemonidae), cardinalfish Astrapogon stellatus, pea crabs (Pinnotheridae) and sea anemones (Actiniaria) have all been found sheltered inside its shell.