The amber pen shell has a pair of long, thin translucent valves and is triangular, fan or wedge--shaped, with its tapered anterior end (umbo) buried and the flared posterior end extending above the sea bottom substratum to facilitate filter-feeding.
The amber pen shell has a pair of long, thin translucent valves that are hinged dorsally by a ligament. Its pointed anterior end (umbo) is usually buried and attached by byssal threads, whereas its wider posterior end extends above the sea bottom surface to facilitate filter-feeding.