SHELL SEEKER: Jewel Boxes From The Sea
The Florida spiny jewelbox (Arcinella cornuta) is a bivalve. Like most
bivalves, it is a filter feeder, feasting on organic particles strained from
the sea. The body of a bivalve is surrounded by the mantle folds and the
two shell plates it produces. A ligament holds the two shell halves tightly
together. The hinge area is where the shell begins to grow. Bivalves are
important food sources for gastropods, fish, shorebirds like sandpipers, and
The Florida spiny jewelbox is about 1 1/2 inches long. It is a thick,
sturdy shell that is off-white in color with an interior that may resemble
the china used for Thanksgiving dinner, shiny and mildly tinted with a pink
to purplish hue. The origin of the name becomes readily apparent with the
discovery of your first specimen. They are shaped like a little jewelry box,
the kind diamond rings are delivered in. Their most distinguishing feature
is the frilly, hollow, spines that protrude from the seven to nine ribs that
cross the shell, originating at the beak (bump above the hinge.) Jewel
boxes are found in warm seas.
Though impressive, their spines aren’t as dramatic as the thorny oyster.
Shells found in deep water, not damaged by strong currents or the impact of
being tossed around by waves, have longer, sharper spines. Often those
found on the beach have smooth, worn-down spines. Flat artificial structures
like concrete slabs often serve as a home for mature specimens that haven’t
been damaged and are wonderful additions to a collection.
One of the fascinating aspects of the spiny jewel box is that when younger
they are fastened to a rock, sea wall, coral, or even another shell
somewhere between the intertidal area (exposed to air during low tide) and
deep water but later in life become detached. The right and left valve are
the same size; in fact the valves are mirror images of each other.