The smooth softshell turtle (''Apalone mutica'') is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of North American

softshell turtle Trionychidae is a family of turtles, commonly known as softshell turtles or simply softshells. The family was described by Leopold Fitzinger in 1826. Softshells include some of the world's largest freshwater turtles, though many can adapt to li ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Trionychidae Trionychidae is a family of turtles, commonly known as softshell turtles or simply softshells. The family was described by Leopold Fitzinger in 1826. Softshells include some of the world's largest freshwater turtles, though many can adapt to li ...

. This freshwater species is

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

to the United States, where it inhabits the

Mississippi River The Mississippi River is the main stem, primary river of the largest drainage basin in the United States. It is the second-longest river in the United States, behind only the Missouri River, Missouri. From its traditional source of Lake Ita ...

system, along with other adjoining waterways that empty into the

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

Geographic range

''A. mutica'' is native to the United States, where it is distributed throughout the central and south-central states. Its natural geographic range extends from western

Pennsylvania Pennsylvania, officially the Commonwealth of Pennsylvania, is a U.S. state, state spanning the Mid-Atlantic (United States), Mid-Atlantic, Northeastern United States, Northeastern, Appalachian, and Great Lakes region, Great Lakes regions o ...

in the east to

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

in the west, as far north as the

Dakotas The Dakotas, also known as simply Dakota, is a collective term for the U.S. states of North Dakota and South Dakota. It has been used historically to describe the Dakota Territory, and is still used for the collective heritage, culture, geo ...

, and south to the westernmost

Florida Panhandle The Florida panhandle (also known as West Florida and Northwest Florida) is the northwestern part of the U.S. state of Florida. It is a Salient (geography), salient roughly long, bordered by Alabama on the west and north, Georgia (U.S. state ...

, where it is eventually replaced by the Florida softshell turtle (''Apalone ferox''). Smooth softshell turtles are common within the

Mississippi River system The Mississippi River System, also referred to as the Western Rivers, is a mostly riverine network of the United States which includes the Mississippi River and connecting waterways. The Mississippi River is the largest drainage basin in the Unit ...

, from its

delta Delta commonly refers to: * Delta (letter) (Δ or δ), the fourth letter of the Greek alphabet * D (NATO phonetic alphabet: "Delta"), the fourth letter in the Latin alphabet * River delta, at a river mouth * Delta Air Lines, a major US carrier ...

Louisiana Louisiana ( ; ; ) is a state in the Deep South and South Central regions of the United States. It borders Texas to the west, Arkansas to the north, and Mississippi to the east. Of the 50 U.S. states, it ranks 31st in area and 25 ...

up to

North Dakota North Dakota ( ) is a U.S. state in the Upper Midwest, named after the indigenous Dakota people, Dakota and Sioux peoples. It is bordered by the Canadian provinces of Saskatchewan and Manitoba to the north and by the U.S. states of Minneso ...

, as well as in the

Colorado River The Colorado River () is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and in northern Mexico. The river, the List of longest rivers of the United States (by main stem), 5th longest in the United St ...

(in

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

), the Brazos,

Sabine The Sabines (, , , ; ) were an Italic people who lived in the central Apennine Mountains (see Sabina) of the ancient Italian Peninsula, also inhabiting Latium north of the Anio before the founding of Rome. The Sabines divided int ...

Pearl A pearl is a hard, glistening object produced within the soft tissue (specifically the mantle (mollusc), mantle) of a living Exoskeleton, shelled mollusk or another animal, such as fossil conulariids. Just like the shell of a mollusk, a pear ...

Alabama Alabama ( ) is a U.S. state, state in the Southeastern United States, Southeastern and Deep South, Deep Southern regions of the United States. It borders Tennessee to the north, Georgia (U.S. state), Georgia to the east, Florida and the Gu ...

and the Conecuh (Escambia) river systems. Two regional

subspecies In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...

of ''Apalone mutica'' have been identified. * The midland smooth softshell turtle (''A. m. mutica''), found throughout the central United States, in and around the Mississippi River. * The Gulf Coast smooth softshell turtle (''A. mutica calvata''), found from Louisiana east to the panhandle of Florida.

Habitat

Both subspecies of ''A. mutica'' are typically found in medium to large, unpolluted fresh waterways, with moderate to fast currents; even in rivers with fast flow, they will swim directly to the sandy bottom and bury themselves, leaving only their nose or eyes exposed as they wait to ambush quickly-passing fish or amphibians. However, they are also found in standing or still bodies of water, like lakes, vernal pools, swamps and marshes. They may also be seen in some canals, reservoirs, or man-made ponds. They prefer water with fine sand or silty, mud bottoms, without heavy boulders, gravel or dense aquatic vegetation. Sandbanks must also be present, as the turtles can be seen sunning themselves for warmth. File:Apalone mutica mutica 157081918.jpg, ''A. m. mutica'' basking, Missouri File:Apalone mutica mutica 169149861.jpg, ''A. m. mutica'' basking with red-eared sliders, Missouri

Description

The smooth softshell turtle has an

anapsid An anapsid is an amniote whose skull lacks one or more skull openings (fenestra, or fossae) near the temples. Traditionally, the Anapsida are considered the most primitive subclass of amniotes, the ancestral stock from which Synapsida and Dia ...

skull, a type of skull structure that was present among the earliest groups of prehistoric reptiles (and retained by turtles today). Primarily, an anapsid skull lacks openings behind the

orbits In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an physical body, object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an satellite, artificia ...

(as opposed to the

synapsid Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rept ...

or therapsid skull). The smooth softshell turtle, as with all softshells, has a smooth, fairly soft, flexible, leather-like

carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the unde ...

that is covered by "skin", as opposed to the hard

scutes A scute () or scutum (Latin: ''scutum''; plural: ''scuta'' "shield") is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of birds. The term is also used to describe the anterio ...

commonly associated with most turtle species. The

plastron The turtle shell is a shield for the ventral and dorsal parts of turtles (the Order (biology), order Testudines), completely enclosing all the turtle's vital organs and in some cases even the head. It is constructed of modified bony elements such ...

is light white or gray, with no notable markings (other than occasional spotting), and its internal anatomy (bones, some organs) may be visible, as it lacks the typically hard shells of other aquatic turtles. It has a tubular snout with round nostrils, sometimes compared to a "pig" nose.

Ernst C Ernst is both a surname and a given name, the German, Dutch, and Scandinavian form of Ernest. Notable people with the name include: Surname * Adolf Ernst (1832–1899) German botanist known by the author abbreviation "Ernst" * Anton Ernst (born ...

, Lovich J (2009). ''Turtles of the United States and Canada, Second Edition''. Baltimore, Maryland: The Johns Hopkins University Press. 840 pp. .

Sexual dimorphism

There is sexual dimorphism between females and males of ''A. mutica'' as females are larger than males. A female has a carapace length of compared to a carapace length of for males. Additionally, the female smooth softshell turtle is usually brown or olive-colored with irregular dark brown blotches, while the carapace of males and juveniles is a brown or grayish color with dark dots or dashes. 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.

Similar species

The smooth softshell turtle may be easily confused with the

spiny softshell turtle The spiny softshell turtle (''Apalone spinifera'') is a species of softshell turtle, one of the largest freshwater turtle species in North America. Both the common name, spiny softshell, and the Specific name (zoology), specific name, ''spinifer ...

(''Apalone spinifera''), as the differences between the two species are subtle. The spiny softshell turtle has a rough carapace with spines along the front edge while, as the name implies, the smooth softshell turtle lacks such spines.Oldfield, Barney; Moriarty, John J. (1994). ''Amphibians and Reptiles Native to Minnesota''. Minneapolis, Minnesota: University of Minnesota Press. 237 pp. . Additionally, the white chin and throat of the smooth softshell are unmarked, compared to the splotchy chin and throat of the spiny softshell. ''A. mutica'' is the only species of North American softshell with round nostrils; all other species have ridges on the nasal septum which make the nostrils C-shaped.

Diet

The smooth softshell turtle is mostly carnivorous, eating aquatic insects,

crayfish Crayfish are freshwater crustaceans belonging to the infraorder Astacidea, which also contains lobsters. Taxonomically, they are members of the superfamilies Astacoidea and Parastacoidea. They breathe through feather-like gills. Some spe ...

, fish and amphibians. Although primarily carnivorous, it sometimes resorts to eating vegetation such as algae, vegetables, fruits, and nuts.

Reproduction

Breeding of the smooth softshell turtle occurs from April to June. The mating system utilized by these turtles is polygyny, 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 from 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 An egg is an organic vessel in which an embryo begins to develop. Egg, EGG or eggs may also refer to: Biology * Egg cell, the female reproductive cell (gamete) in oogamous organisms Food * Eggs as food Places * Egg, Austria * Egg, Switzerland ...

not more than 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 and have a carapace length of . 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.Nagle, Roy D., et al. (2003). "Parental investment, embryo growth, and hatchling lipid reserves in softshell turtles (''Apalone mutica'') from Arkansas." ''Herpetologica'' 59 (2): 145-154. This energy is more 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

The smooth softshell turtle is the most aquatic of the softshell turtles as it is often referred to as a "swimmer". It is able to stay underwater for extended periods of time due to its long neck and tubular snout. It often buries itself in the sand substrate at the bottom of a river or pool just deep enough so that its snout barely reaches the surface. Additionally, the skin covering the shell allows for a high rate of gas exchange. This enables the turtle to stay submerged for a long period of time. In this position, it often waits for prey to pass and utilizes its long neck to capture the prey. The smooth softshell turtle hibernates in the months of October to March. It hibernates by burying itself in substrate underwater. After emerging from hibernation, it is often found on land basking in the sun. Given that its shell is a soft shell, it is unable to stay in the sun for extended periods of time. When basking, it is wary of its surroundings, and if any threat presents itself, it is quick to abandon its basking site to seek safety. Its agility on land and water makes it a difficult prey item for predators such as raccoons, humans, alligators and snapping turtles. It seeks shelter from these threats by diving and concealing itself in mud.

Conservation status

Currently, the smooth softshell turtle is considered a species of least conservation concern. However, the species is still facing some wide-ranged threats. These threats include habitat degradation, harvesting for food, and an increase in human disturbances at nesting sites. Additionally, due to its skin's high rate of gas exchange, it is very susceptible to polluted waters. As a result of all of these factors, the smooth softshell turtle has been listed as a species of special concern in Minnesota and Wisconsin.

Subspecies

Two

are recognized, including the

nominotypical subspecies In biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics ( morphology), but that can successfully interbreed. ...

. *'' Apalone mutica calvata'' *'' Apalone mutica mutica'' ''

Nota bene ( ; plural: ) is the Latin language, Latin phrase meaning ''note well''. In manuscripts, ''nota bene'' is abbreviated in upper-case as NB and N.B., and in lower-case as n.b. and nb; the editorial usages of ''nota bene'' and ''notate bene'' fi ...

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

Sympatric species

''Apalone mutica'' is

sympatric In biology, two closely related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter each other. An initially interbreeding population that splits into two or more distinct spe ...

with the spiny softshell turtle ('' Apalone spinifera'') over much of its

range Range may refer to: Geography * Range (geographic), a chain of hills or mountains; a somewhat linear, complex mountainous or hilly area (cordillera, sierra) ** Mountain range, a group of mountains bordered by lowlands * Range, a term used to i ...

.Williams, Thomas A.; Christiansen, James L. (1981). "The Niches of Two Sympatric Turtles, ''Trionyx muticus'' and ''Trionyx spiniferus'', in Iowa". ''Journal of Herpetology'' 15 (3): 303-308
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