How Scallops Swim Without Fins (2 Photos)

A shell sitting on the ocean floor isn't necessarily stuck in place. Scallops are capable of swimming, using their own shell valves as a built-in propulsion system.





Mollusks on the seafloor, captured by the HabCam underwater imaging system. NOAA Fisheries.

The mollusk rapidly snaps its shell shut, forcing water out to produce jet propulsion. As the valves spring open again, another quick contraction follows. From the outside, it looks as though the shell is repeatedly clapping—which is precisely how NOAA Fisheries describes the motion.



A scallop swimming past the lens of the HabCam underwater imaging system. NOAA Fisheries.

These images from the HabCam camera system show both a scallop mid-swim and sedentary mollusks resting on the seabed. For scallops, the shell serves a dual purpose: defense and locomotion. No fins required.