SLIPPER SNAILS
Although I usually say that shelling on Tybee is “weird” because you
never know where you will find shell beds washed up on the beach, Tybee
Island has a good diversity or variety of shells. Many of them are small
species, but we get shells produced by animals that typically live to our
north as well as those that live in the sub-tropics to our south. So as the
seasons change and the tides change, our shells get re-supplied and
redistributed.
To me, one of the most interesting shells we get around here, usually
washed up among the other shells near the high tide line, is the Slipper
shell. A Slipper shell is produced by a snail, but Slipper Snails are a little
strange, as are their shells. The shell isn’t a typical snail-looking shell with
a lot of spiral whorls. In fact, you have to look closely, and maybe even use
your imagination a little, to notice the slight amount of spiraling of the shell.
From the top, or outside, the shell looks more like it belongs to a clam-like
bivalve mollusk. But when you turn it over and look at the bottom, or inside,
you notice a distinct shelf that extends half-way across the bottom of the
opening. And just to make things even a little more confusing, it turns out
that the wide, open end is actually the front end of the animal, and the
narrower shelved end is the posterior.
Slipper Snails live attached onto something hard rather than plowing
through the sand (like Moon Snails and Lettered Olive Snails) or actively
crawling around on rocks grazing or preying on other animals (like Oyster
Drills and Florida Rock Snails). Being attached and non-motile, Slipper Snail
movement and distribution is determined by the animal they are attached
onto. The most frequent animals I see them attached onto around here are
Horseshoe Crabs, Hermit Crab shells, and sometimes inside Whelk shells.
A Slipper Snail’s attachment onto the surface or substrate is quite strong.
28 TYBEE BEACHCOMBER | NOV 2020
They have a muscular foot on the base of their body that pretty much covers
the entire inside space of the bottom opening of the shell. With it, a Slipper
Snail can pull the shell down and create a strong suction onto the surface.
When they do this, it is almost impossible to pull or pry a Slipper Snail off
its surface. They are plankton eaters, filtering tiny food particles out of the
seawater that they pull into their body from underneath the shell.
You can actually find shells from 3 different species of Slipper Snails here
on Tybee. The largest is the Common Atlantic Slipper Snail. When alive you
might find them stacked on top of each other, with the oldest and largest
on the bottom. That one will become a female; and younger smaller ones
stacked above it will remain as males. All of them start out as males, but
the biggest, oldest one changes to be female. The White Slipper Snail has a
thin, flat, white shell, and I’ll often find live ones inside of Hermit Crab shells
or on flatter surfaces. The Convex Slipper Snail is small and its shell may be
only a half-inch long. Its shell is dark red or purple, and I’ll usually see them
stacked on Hermit Crab shells.
Dr. Joe Richardson (Ph.D. Marine Sciences) is a retired marine science
professor with 40 years of research and teaching experience along GA,
the southeastern coast and Bahamas. Besides research, he conducts Tybee
Beach Ecology Trips (www.TybeeBeachEcology.com) and frequently posts
pictures of their findings on his Tybee Beach Ecology Trips Facebook page.
Beach Walks
with Dr. Joe
By Dr. Joe Richardson
/(www.TybeeBeachEcology.com)