Shell of the Week: The Southern Horse Mussel
Modiolus squamosus Beauperthuy, 1967 is the less uncommon among the local mussel species. Scattered valves and even complete pairs may be found on local Southwest Florida beaches after storms, particularly during the winter. The species may grow to 65 mm (about 2.6 inches), and the external shell surface is covered with a relatively thin, light-brown periostracum, which contrasts with the distinctive purplish color of the internal surfaces. Southern Horse Mussels can be distinguished from the American Horse Mussel by the orange color of the inside of the valves (instead of purplish), and by the more “obese” shell on the latter.