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The smooth softshell turtle (Apalone mutica) is a species of softshell turtle of the family Trionychidae. The species is endemic to North America.

Geographic distribution
A. mutica is native to North America. It is distributed throughout the central and south-central United States as their range extends from Pennsylvania to New Mexico and south to the Florida panhandle. Smooth softshells turtles inhabit the Mississippi River drainage from Louisiana up to North Dakota, as well as the Colorado, Brazos, Sabine, and Pearl, Alabama and Escambia river systems. Two subspecies of A. mutica have been identified. Midland smooth softshells, "Apalone mutica mutica", are found throughout the central United States. The other subspecies,"Apalone mutica calvata", is found ranging from Louisiana to the panhandle of Florida. Both subspecies are typically found in medium to large unpolluted rivers with moderate to fast currents, but are also found in standing water bodies like lakes, ponds and marshes. They prefer water with sand or mud bottoms, without rocky areas or dense vegetation. Sandbanks must also be present.

Description
The smooth softshell turtle has an anapsid skull. This kind of skull is present among the earliest reptiles and is retained by turtles today. The anapsid skull lacks openings behind the orbits. Moving down the the body, the smooth softshell turtle has a smooth, flexible and leather like carapace that is covered by skin instead of the hard scutes commonly observed in other turtle species. The plastron is light (white or gray) with no markings, and the underlying bones are visible. Smooth softshell turtles have a tubular snout with round nostrils that are in the inferior position. There is sexual dimorphism between females and males as females are larger than males. A female has a carapace length of 16.5-35.6 cm compared to a carapace length of 11.4-17.8 cm in males. Sexual dimorphism is also apparent in the size of the tails and claws. Males have thicker tails than females, but females have longer hind claws than males. Smooth softshell turtles may be easily confused with the spiny softshell turtle (Apalone spinifera), as the differences between the two species are subtle. Spiny softshell turtles have a rough carapace with spines along the front edge while, as the name implies, smooth softshell turtles lack such spines. Additionally, their white chin and throat are unmarked, compared to the splotchy chin and throat of the spiny softshell.

Diet
Smooth softshell turtles are most carnivorous, eating aquatic insects, crayfish, fish, and amphibians. Although primarily carnivorous, they sometimes resort to eating vegetation such as algae, vegetables fruits, and nuts.

Reproduction
Breeding of the smooth softshell turtle occurs from April to June. The mating systems of these turtles is polygynous, meaning that males will mate with more than one female. Males actively seek out females by approaching other adults. If the other party is male or a non receptive female, aggression may be displayed. However, if the other party is a receptive female, she remains passive to the advancements of the males. Copulation usually occurs in deep pools as the male mounts the female. The nesting period is usually form May to July as females only lay eggs once a year. During this period adult females of A. mutica lay clutches of 3 to 28 eggs not more than 100 m from water in sandy areas. Eggs generally hatch 8 to 12 weeks later with the highest frequency of hatching being between August and September. Hatchlings average a weight of 5.4 g and have a carapace length of 4 cm. Male smooth softshell turtles become sexually mature during their fourth year and females become sexually mature during their ninth year.

Female turtles offer prenatal care for their offspring. They produce high levels of non-polar lipids that provide energy for their growing embryos. This energy is more than than enough to keep the embryos alive. The high concentration of lipids also offer an advantage at birth as it acts as a food source until they hatchlings become mature enough to commence feeding. This type of care is also known as parental investment in embryogenesis. However, after hatching no physical parental care is given.

Life History
Smooth Softshell turtles are the most aquatic of the softshell turtles as they are often referred to as "swimmers". They are able to stay underwater for extended periods of time due to their long neck and their snout. The often burry themselves in the sand substarate at the bottom of the river or pool just deep enough so that their snout barely reaches the surface. Additionally, the skin covering the shell allows for a high rate of gas exchange. This enables the turtles to stay submerged for a long period of time. In this position they often wait for prey to pass and utilize their long neck to capture their prey.

These turtles hibernate in the months of October to March. They hibernate by burying themselves in substrate underwater. After emerging form hibernation, these trutles are often found on land basking in the sun. Given that their shell is a soft shell, they are unable to stay in the sun for extended periods of time. When basking, they are wary of their surroundings and if any threat presents itself, they are quick to abandon their basking site in seek of safety. Their agility on land and water make them a hard prey for predators such as raccoons, humans, alligators and snapping turtles. They seek shelter from these threats by diving and concealing themselves in mud.

Conservation Status
Currently, this species is of relatively low conservation concern and does not require significant protection or major management. Localized threats may exist, but on a range-wide scale no major threats are known. Localized threats may include habitat degradation, harvesting for food, and an increase in human disturbances at nesting sites. Due to the the high rate of gas exchange rate, their thin skin is susceptible to polluted waters. However, due to all of these factors, the smooth softshell turtle has been listed as a species of special concern in Minnesota.

Subspecies
Two subspecies are recognized, including the nominotypical subspecies.


 * Apalone mutica calvata (Webb, 1959)
 * Apalone mutica mutica (Lesueur, 1827)

Nota bene: A trinomial authority in parentheses indicates that the subspecies was originally described in a genus other than Apalone.

Sympatric species
Apalone mutica is sympatric with the spiny softshell turtle (Apalone spinifera) over much of its range.