Busy, Busy, Bruised Nassa
With a shell reaching only 15 mm (about 0.6 inch), the Bruised Nassa, Phrontis vibex (Say, 1822), is one of most abundant snails in the back bays and sand and mud flats of Southwest Florida. Its shell has a sculpture of 7–12 axial ribs crossed by fine spiral lines of variable size. When it comes to color pattern, the Bruised Nassa is a very variable species, with assorted alternatives around the theme of specks and spots on a lighter background.
The image above shows a live Bruised Nassa gliding on the acrylic wall of one of the Museum new aquariums, in February 2020. The snail’s eyes are located near the bases of each tentacle. The siphon is extended to “smell” the ambient water, and the short, orangish snout is probing the acrylic for morsels of food. The front part of the foot (on the left), just under the head, is called the propodium. It acts as a shovel, or snowplow, helping the snail bury or move on the sand surface. The back of the foot (on the right) bears a couple of small epipodial tentacles, which apparently have a sensorial function, alerting the snail of approaching predators.
Bruised Nassa are voracious scavengers, feeding on decaying bodies of invertebrates, fish, and other marine animals. They are capable of detecting the carcasses of dead marine animals from long distances and darting at relatively high speeds to feed on them. I photographed the image below on a sand flat off Bunche Beach, in Fort Myers, Florida. It shows several Bruised Nassa proficiently feeding on a small horseshoe crab carapace left on the flat during low tide. Read more about local mollusks in the Museum’s Shell Guide.