Softshell Turtle

The Softshell turtles belong to the family Trionychidae are freshwater species. About 30 different species of turtles are characterized by a flattened shells. Usually, the soft shell snapping turtles lack epidermal scutes, which means large scales. One of the important characteristics of the softshell turtle is the leatherback sea turtle, they do not have the bony architecture of the shell.   An example of leatherback sea turtles is Dermochelys coriacea. Usually, the softshell turtles have long necks and streamlined heads with elongated proboscis-like snouts bearing the nostrils at the tips. 

The soft shell snapping turtles prefer to lie buried under the mud, sand and shallow water. These turtles will extend their head and neck, through the snout, they can just break the surface and start to breathe in a snorkel-like manner. All the species of softshells are carnivorous species. They can actively search for their prey or capture it by ambush. Generally, the flattened shape seems a strange one for an active animal. But they are hydrodynamically efficient. The Trionychidae can propel by using all four limbs, Both forefeet and hind feet are strongly webbed and support them for rapid swimming. 

About 14 genera of softshell turtles are majorly classified into two evolutionary groups. The species belongs to the subfamily Cyclanorbinae spread over in the regions of southern Asia, northeastern Africa, and sub-Saharan Africa. Further, the species belonging to Trionychinae are spread over the region of southeastern North America, southern Asia, and Africa. The species of Cyclanorbine mainly contain two African genera namely, Cyclanorbis and Cycloderma, Burnam flap shelled turtles and a single Indian genus Lissemys. The softshell turtles of the Trionychine subfamily are of biologically diverse species.   

Three species of North American softshell turtles, Apalone are in moderate size and adult males turtles can grow about two-thirds the size of their female turtles.  The length of the adult female of  A. mutica and A. spinifera carapace range is about 17cm. And the length of the A. ferox species is about 63cm. One of the largest Trionychine softshell turtles is the narrow-headed softshell turtle, whose scientific name is Chitra indica. Pelochelys bibroni, the  Asian giant softshell of southeast Asia is also one of the largest species. Both species can reach a length of more than 1 metre. 

Usually, Softshell turtles can lay about 2 eggs like young females of the genus Lissemys. And some species like large-bodied Trionyx triunguis softshell turtles can lay up to 100 eggs. The time period for attaining complete embryonic development of the turtle can vary from less than 30 days to 300 days. The embryonic development of the turtles completely depends on the type of species and environmental conditions of the nest. They use their hind limbs to dig nests in friable soil, which are adjacent to water.

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The above image shows the softshell turtles, which have long heads present in the land. 

Physical Characteristics of Softshell Turtle 

As the name shows, the softshell turtles do not have carapaces or bony structures. They have spiny softshells, which project like scales.  The carapace on the sides of the turtles looks leathery and pliable. Also, the central part of the carapace has a layer of solid bone, like other turtles. But these bones are absent at the outer edges of softshell turtles. Some species of these turtles have dermal bones in the plastron, but these are not attached to the bones of the shell. The light and flexible shells in the soft shell snapping turtles allow them to move easily in open water or in muddy lake bottoms. Also, the soft shells on the turtles allow them to move faster on land, which is compared to other turtles. The feet of turtles are webbed and three-clawed so their family names are termed Trionychidae. The colour of the carapace of each species of turtle depends on the sand or mud colour of its geographical region, which assists the turtles in the "lie in wait" feeding methodology.

The characteristics of turtles completely depend on their aquatic lifestyle. Many species of turtles are submerged under the water to swallow their food. The softshell turtles have elongated soft, snorkel-like nostrils. Necks of softshell turtles are disproportionately long in comparison to their body sizes, which enable them to breathe surface air. While the body of the turtle remains submerged in the mud or sand and their foot remains below the surface.

Most of the softshell turtles are carnivore species, they include fish, aquatic crustaceans, snails, amphibians in their diet. Sometimes, they include birds and small mammals in their diet. 

Usually, the softshell turtles can breathe underwater with rhythmic movements of their mouth cavity. Further, these turtles contain numerous processes to supply air with blood, acting similarly to gill filaments in fish. By using this method, the turtles will stay underwater for a prolonged period. The Chinese softshell turtle can excrete more urea while they are breathing under the water. Also, this is one of the efficient solutions for the turtles, who does not have sufficient access to freshwater, especially the turtles in  brackish-water environments

According to the study of Ditmars in 1910, The bones of many species form the outer border of powerful crushing processes, which was allowed by their alveolar surfaces of the jaws. They are assisting them to ingest tough prey such as molluscs. The jaws of turtles make large turtles dangerous, which are capable of cutting a person's finger, or possibly their hand

Some turtles determine their sex depends on temperature. But the species of Trionychids have ZZ/ZW genetic sex determination of baby softshell turtle. Microchromosomes in the turtles play important role in sex determination. Usually, the turtles will show several sexual dimorphisms. The female turtles can grow up to several feet in carapace diameter, sometimes the male turtles remain smaller than the female turtles. 

Habitat of Softshell Turtles 

The softshell turtles have soft and flattened shells, which enables them to remain submerged under the water for a long period. These turtles have many biological adaptations for their aquatic life. 

Pharyngeal Breathing

Usually, softshell turtles hibernate during the winter. During the hibernation period, they bury themselves under the sand and mud at the bottom of a river, lake, or pond. Also, these turtles do not require food during the hibernation period. But they still require enough oxygen to survive  While undergoing the hibernation process, the turtles are using pharyngeal breathing. These turtles can absorb oxygen through the skin and the lining of their throat, or pharynx. 

Some softshell turtles can absorb 70% of the required oxygen through their skin and the remaining 30% of the air is absorbed by the animals pumping water in and out of the pharynx. The softshell turtles have many villi, or small projections of tissue, within the pharynx that has a supply of blood vessels. These villi provide a large surface to absorb enough oxygen for their survival. But the pharynx breathing underwater is unique and differs from the general mechanisms. 

But other species of turtles will use the cloaca for breathing under the water. Usually, the cloaca remains open at the back of the turtles. They also use cloaca for excretory, digestive, and reproductive systems. These turtles have cloacal bursae, which look like a pair of small pockets to enrich the blood supply. Further, they allow the turtles to remove oxygen from circulating water as pharynx in the softshell turtles. 

Special Adaptations of Softshell  

As the softshell turtles do not have hard shells, they need to have unique adaptations for surviving in the environment and to avoid predation. The softshell turtles can swim rapidly, which will help them to speed and catch the prey or to escape from predators. Also, the turtles have strongly webbed feet, which enable them to move in water and land at surprising speed. Also, the flattened shape of softshell turtles has hydrodynamically efficient, helping them to move quickly.

Hibernation

Softshell turtles are widely found in the temperature region of the earth. Sometimes, the remains are active throughout the year, but the species found in the northern regions will undergo hibernation during the cold temperatures. During the hibernation period, the turtles will go into brumation, which is the same as the dormancy period experienced by reptiles. The hibernation of turtles is much similar to that of mammals. Turtles are ectothermic species, which means they are cold-blooded species.  Also, the environment influences them to maintain internal body temperature.

When the temperature of the water begins to decrease below the preferred level, the turtle falls into hibernation. The lower atmospheric temperature decreases the entire metabolic rate of turtles. So, they began to store energy and oxygen in the water to meet their minimal needs. 

While the environmental temperatures increase during the spring, the water warms, and the turtles return to their routine work.

Types of Softshell Turtles 

Indian Softshell Turtles:  Nilssonia gangetica is an Indian softshell turtle that is widely spread over the rivers in South Asia such as Ganges, Indus and Mahanadi. These species are vulnerable species, whose carapace length is about 94 cm. They mainly include fishes, amphibians, carrions and other animal matter and aquatic plants in their diet. 

Black Softshell Turtles: Nilssonia nigricans is a Black softshell turtle that is widely found in freshwaters of Assam and Bangladesh. Long back the Indian softshell turtles and Peacock softshell turtles were also considered black softshell turtles. Later they are identified and classified as separate species. They are the native species of the Brahmaputra river. 

Florida Softshell Turtles: The Florida softshell turtle is one of the large turtles with a flattened, pancake-like body, a long neck, an elongated head with a long snorkel-like nose, and large webbed feet. They are the native species of  South Carolina, Georgia, and Alabama.

Spiny Softshell Turtles: The spiny softshell turtles are the largest freshwater turtle species, which are widely found in North America. These turtle shells look soft, flat, and rubbery. Adult female species can reach the maximum length of 7 to 19 inches, but the male turtles remain at 5 inches. They have pig-like noses and webbed feet

Chinese Softshell Turtles: Pelodiscus sinensis is the scientific name of Chinese softshell turtles. These are one of the softshell turtles that are endemic to China. The population of Chinese softshell turtles are in a wide range, present in other Asian countries, as well as Spain, Brazil and Hawaii. 

Asian Giant Softshell Turtles: Pelochelys cantorii is the scientific name of Asian giant softshell turtles are also known as Cantor's giant softshell turtle and the frog-faced softshell turtle. They are freshwater species, widely distributed over southeast Asia. These Asian giant softshell turtles are one of the largest extant freshwater turtles. 

Albino Softshell Turtles: Albino softshell turtles are the world's smallest growing softshell turtles. The Albino softshell turtles have a weird and strange creature called a softshell turtle which is the native breed of America.  

Peacock Softshell Turtles: Nilssonia hurum is the scientific name of Peacock softshell turtles. They are the native species of  South Asia. Further, the Peacock softshell turtles are listed in IUCN Red List as a vulnerable species. They are not aggressive species as other softshell turtles. 

Smooth Softshell Turtles: The Smooth softshell turtles are the most endemic species in North America. Apalone mutica is the scientific name of Smooth softshell turtle.  They are one of the medium to large freshwater turtles.  They are mainly inhabited in the Mississippi River drainage from Louisiana up to North Dakota and Pennsylvania, as well as the Colorado, Brazos, Sabine, and Pearl, Alabama and Escambia river systems.

Threats to Softshell Turtles 

Many species of turtles are facing threats from human beings. The habitat destruction and population of turtles are not only destroying the living turtles but also impact the availability of prey for turtles.  Some species of softshell turtles are hunted for food and medicine. About more than half of the species of softshell turtles are listed as endangered species by the  International Union for Conservation of Nature (IUCN).