A first report on the shrimp Pontonia sp and other potential symbionts in the mantle cavity of the penshell Pinna carnea in the Dominican Republic

Examination of the mantle cavity of 310 penshells Pinna carnea, collected from seagrass beds in southwestern Dominican Republic, revealed the presence of four species from three phyla as potential symbionts. The shrimp Pontonia sp. was found in 178 penshells, the cardinalfish Astrapogon stellatus in 18, an anemone (order Actiniaria) in two, and a pea crab (family Pinnotheridae) in one. The penshell likely provides these organisms with a refuge from predators. It also provides nutrition for shrimp as they consumed food trapped in the mucus secreted by the penshell host. All of the cardinalfish, and 91% of the shrimp, were found in penshells measuring > 150 mm in hinge length. At approximately 150 mm, the shells of P. carnea thicken and so flatten less when the valves are closed. As a result, larger penshells provide more mantlecavity space for accommodating organisms. Shrimp and cardinalfish size increased with the size of the host penshell. The positive relationship between shrimp size and penshell size, a prevalence of male-female pairs of shrimp and other field observations, suggest that a long-term association exists between shrimp and penshells, and that the mating system of the shrimp involves social monogamy.