North American Soft-Shell Turtles, Apalone species
by C. Dee Dillon
Drawing by Robert Savannah, USFWS
Currently, there is a certain amount of confusion regarding classification (taxonomy) in the soft-shell family
Trionychidae. If you look at the latest version of Pritchard's Encyclopedia of Turtles (1979), you will find
a total of eight different genera in two sub-families. If you look at Iverson's A Revised Checklist with
Distribution Maps of the Turtles of the World (1992), you will see 14 different genera in the same two
sub-families. Not only are there more genera, the genus name of North American soft-shells has "changed" from
Trionyx to Apalone (Amyda has also been used). I will use Apalone here although I must admit
I'm not used to it myself. I will confine myself in this article to the North American or New World soft-shells,
although a lot of the habits and characterizations apply to many soft-shelled turtles around the world.
There are soft-shell turtles in North America, Asia and Africa. In North America, Iverson recognizes three species and 9 subspecies: two in Apalone mutica; seven in Apalone spinifera; and no subspecies in Apalone
ferox. The Florida soft-shell, Apalone ferox, resides in South Carolina, Alabama, Georgia and of course Florida. The smooth soft-shell turtle, Apalone mutica, can be found throughout the entire central USA. The spiny soft-shell turtle, Apalone spinifera, is distributed throughout most of the USA and northern Mexico with the exception of the northwestern US.
I apologize ahead of time for the lengthy physical description, however, soft-shell turtles are very different from "the rest" of the turtles and tortoises that we are accustomed to, and I believe it is necessary. Archie Carr states
that soft-shell turtles have existed in their present form since the middle Cretaceous period, 135-65 million years ago. It would have started its split from the other turtles even earlier.
The soft shell (bony part) is substantially different in a soft-shelled turtle from that of a "normal" turtle. The peripheral bones are gone or reduced in number, allowing the leathery edges of the shell to "flap". The plastron is
cartilaginous or incompletely ossified. The turtles are covered by a leathery skin, not scutes. The shell is low in profile and round in outline (adults generally have a more elongated shape). The feet are highly webbed and three-clawed (hence the tri in Trionyx). The head and neck are withdrawn into the shell with vertical bends as
with other Cryptodiroidea. The neck is quite long and the head narrow with a double-barreled proboscis for a nose. The
long nose is excellent for snorkeling and "sniffing" amongst cracks and crevices for food.
The Florida soft-shell is the largest of the New World soft-shell turtles (which are all believed to have
originated in the Old World) and has the most Old World characteristics such as: relatively large size, tolerance for
brackish water and longitudinally wrinkled carapace. The young Florida soft-shell is olive-yellowish in color with
large gray spots, yellow and orange markings on the head and a yellowish border around the carapace, (perhaps the most
beautiful of the North American "softies"). These juvenile markings are mostly lost with age. Adults are brown-gray
sometimes showing traces of the juvenile markings. The plastron of the juveniles is a beautiful slate-gray.
The spiny soft-shell has a brownish/olive background color to its carapace with many variations of darker markings and ocelli on the Eastern specimens and white spots on the Western specimens, dependent upon subspecies. The spiny
soft-shell gets its name from the cone like projections on the leading edge of its carapace.
The smooth soft-shell gets its name because to a large degree it lacks the spiny protuberances of its relative.
Smooth soft-shells have faint markings as juveniles on a tan carapace with light colored markings on the side of the
head. Adults often develop a darker mottled brown color on the carapace. Plastrons of smooth soft-shells are very
light or white in color with visible callosities.
Soft-shell turtles are believed to breathe anally and pharyngeally as well as "normally". This means that there is direct oxygen transfer through highly vascular papillae in the turtles throat and anus. Continuous movement of the
hyoid bone (in the throat) pumps water over the vascular tissues somewhat like the action of gills in fish. This appears externally in the continual swallowing movements observed in soft shells while submerged.
Wild Habits & Food
In the wild soft-shell turtles inhabit all types of waters and waterways, from streams and rivers to lakes ponds
and sloughs. They spend most of their time in the water or buried in the substrate at the bottom. They burrow into the
mud or sand and extend their long neck to the surface for air or ambush passing fish from hiding. They bask on the
banks of their water homes but rarely if ever on logs, rocks or each other (unlike many of our harder shelled
buddies!). They can move extremely quickly in water or on land. In fact, they are probably the fastest turtles on
land. They eat just about anything you find in the water, including but not limited to: fish, snails, insects,
amphibians, carrion, crayfish and some plant material. They lay from 4 to 33 hard spherical eggs, about 1"-1.2" in
diameter, depending on size, species and range. Some larger adults have been found to exhibit greatly enlarged jaw
surfaces perhaps indicating a preference for mollusks.
If you plan to keep soft-shell turtles indoors, plan on a big aquarium and filter system, frequent water changes or filthy water! These guys are messy. They are active and strong enough to move most aquarium "furniture" and undermine anything and everything as they attempt to burrow into the substrate. They grow fairly quickly because they get most
of the food in community settings. We have moved all of ours outside and they have flourished. Soft-shell turtles are
very susceptible to shell rot and fungal infections on both plastron and carapace, especially in community settings
indoors. Minor scratches turn into life threatening infections. If you buy a soft-shell turtle make sure its shell is
flawless both top and bottom. Fighting the infections, once started, is very difficult and frustrating. Giving an
injection to an unwilling soft-shell turtle redefines challenging. Prevention is the key here. We have found that
sunshine, fresh air and space are the best preventatives. Wounds seem to heal themselves outdoors.
Soft-shell turtles can be very aggressive, and they sometimes bite each other and "unrelated" turtles spontaneously or when feeding. I have seen soft-shell turtles continue to kill fish long after they have stopped eating, and just
let the dead fish rot. I have lost more skin hand feeding soft-shell turtles than any other turtle, (they have a very
sharp ridge on their palate). We had a large female (about 13" diameter) that was causing so many injuries to other
turtles we had to adopt her out to an owner with a less populated and larger pond. The other remedy for soft-shell
disagreements is enough space for the less dominant ones to escape. Our current group of five (I think) get along
reasonably well or have enough room (8,000 gallons in three interconnected ponds) to stay out of each others way. When
we first moved them outside I worried that the concrete ponds would scratch their plastrons and that other turtle
claws would scratch their carapaces. This simply hasn't happened, or they heal so fast outside in the "fresh" air I
can't see it happening! They also appear to lift themselves up slightly before they launch themselves into the pond
Our adult smooth soft shells have mated and laid in our yard the last two years. In 1995 we found only one
hatchling (staring up at me from the grass) which we raised inside for one season and then adopted out. This past year
we had four discovered by our son while he was weed whacking (only one casualty) and they were adopted out. Now that
we now where she nests we might be able to bring future eggs inside for, hopefully, better results.
All of our outdoor aquatics get a mixed diet including: Purina trout chow, goldfish, fat-heads, imitation crab (by hand), and occasional Pacific Ocean fish that we catch but don't always eat, such as: bonito, barracuda, mackerel, kelp bass, sheephead and ocean white fish. There is always water hyacinth in the ponds and they do eat it at times. I have never seen ours more than 2' from the edge of the ponds while basking, but the nest site is somewhat further
Shortly after getting our first turtle, I saw a soft-shell turtle in a pet store and I was hooked (then I saw a
picture of a Mata Mata and there was no turning back). They are very active and fun to watch in aquariums, but they
really need a lot of room if you are going to keep one indoors or out.
Carr, Archie. 1952. Handbook of Turtles, New York. Cornell University Press.
Iverson, John B. 1992. A Revised Checklist with Distribution Maps of the Turtles of the World, Indiana.
Pritchard, P.C.H. 1979. Encyclopedia of Turtles, New Jersey. T.F.H. Publications, Inc. Ltd.
Originally published in the Tortuga Gazette 33(6): 1-4, June 1997