Tiny Bubbles
You might imagine marine snails crawling
around on the sea floor. But thanks to a unique
adaptation, one family of snails lives life at the top
of the ocean.
Violet snails cannot swim but they can construct
"rafts" from clusters of air bubbles, and these rafts
allow the snails to float at the water's surface. They
float throughout tropical and subtropical oceans,
preying on an abundant food source − jellyfish.
To construct a raft, the snail sticks part of its
muscular foot just above the water and cups the
foot to enclose a pocket of air. Glands on the foot
secrete a tacky mucus that quickly seals the air in
a bubble. To make its float larger, the snail presses
the newly created air bubble onto the existing
cluster of bubbles, and as the mucus hardens, the
bubble adheres to the rest of the "raft." Part of the
snail's foot grasps onto the raft at all times, and
the snail floats upside-down in the ocean.
Curiously, violet snails are closely related to − and
thought to have evolved from − a family of snails
that dwell on the ocean floor. How did they go from
a bottom-dwelling lifestyle to one that relies on
access to air?
It is possible that egg capsules produced by
bottom-dwelling snails occasionally trapped air
which lifted the egg capsules and the female that
produced them to the surface. Over time, these
bubble masses could have evolved to function as
rafts instead of egg-carriers − allowing violet snails
to rise to the top.