Discover the nudibranchs of Florida. These colorful sea slugs
lack shells and carry their gills on the outside of their bodies.
Find out how they are useful in scientific research.
Molluscs include familiar invertebrates such as snails, clams,
scallops, oysters, slugs, squids, and octopuses. Used as food,
decoration, tools, medicine, and in the aquarium trade, they have
benefited people for millenia. A lesser-known molluscan group is
the nudibranchs, commonly called "sea slugs," which display
a fascinating variety of colors and body forms.
Nudibranch (pronounced nu-da-brank)
means "naked gill," an apt name because their gills are
external. Some nudibranchs have gills towards the rear.
Others have rows of respiratory projections called cerata
situated along the body. On the front end of the nudibranch is a
pair of rhinophores (rhino = nose, phore = carrier). These
structures are sensory organs that detect chemicals in the water,
similar to a sense of smell. Both the gills and the rhinophores can
be retracted into specialized pockets for protection. A nudibranch
feature that is unique to molluscs is the radula, which they use to
eat sponges, corals, anemones, hydroids, bryozoans,
tunicates, algae, and sometimes other nudibranchs. The radula
acts like a cheese grater, moving back and forth to grasp and shred
the food. Nudibranchs that have cerata are capable of storing the
tiny stinging cells called nematocysts that are in
the corals, hydroids, or anemones that they eat. Then they use
those stinging cells for their own defense.
nudibranchs have bright color patterns, which warn predators to
keep away. Several nudibranchs have glands along the bottom
of the mantle that store the poisonous chemicals derived from
their food, and by associating bright color with bad tastes,
predators may leave them alone. Such warning coloring is called
aposematic coloration. However, not all predators are deterred.
Several animals, such as sea spiders, polychaetes, sea stars, and
some crabs, target nudibranchs as food.
Most nudibranchs live up to a year, although four-year-old
nudibranchs have been found. They come in various shapes and sizes,
ranging from 1/8th inch (4 millimeters) to 2 feet (60 centimeters).
Nudibranchs have an interesting life cycle. They are
hermaphroditic, which means they possess both female and male sex
organs, and reproduce by cross-fertilization. When nudibranchs
reach maturity, they find a partner. Shortly after mating, they lay
their eggs in a ruffled ribbon-like strand or in a
cluster. The young may develop indirectly, hatching as
free-swimming planktonic or pelagic larvae called veligers (the
only time they have a shell); or they may develop
directly into small, crawling, adult-like juveniles.
Scientists study nudibranchs for several reasons. They are
an "indicator species" showing the health of
their environment. They help us understand evolutionary
processes, such as having a shell or no shell and using nematocysts
for defense. Nudibranchs are medically important because the toxic
compounds in the creatures they eat are powerful chemical agents
that can deter the growth of cancer cells. Scientists who
study learning and memory use nudibranchs' large,
simple neurons in their research.
Nudibranch Photo Gallery
The Fish and Wildlife Research Institute (FWRI) collects data
directly from people who harvest aquatic species, including
nudibranchs, in order to monitor harvest rates and assess the
health of fish and invertebrate populations. The
Fisheries-Dependent Monitoring (FDM) section at FWRI maintains
marine-life landings data dating back to 1994. To
view landings data, view the article Commercial
Fisheries Landings in Florida.
For more information about Florida's marine-life fishery
for the aquarium trade and the data collected, view the article Marine Life and
A few other nudibranchs that are also found in Florida
Unless otherwise noted, all images are
credited to the Florida Fish and Wildlife Conservation Commission