| Trionychidae | |
|---|---|
 | |
| Chinese softshell turtle Pelodiscus sinensis | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Testudines |
| Suborder: | Cryptodira |
| Superfamily: | Trionychia |
| Clade: | Pan-Trionychidae Joyce et al., 2004 |
| Family: | Trionychidae Fitzinger, 1826 |
| Subfamilies | |
Trionychidae is afamily of turtles,commonly known assoftshell turtles or simplysoftshells. The family was described byLeopold Fitzinger in 1826. Softshells include some of the world's largest freshwater turtles, though many can adapt to living in highlybrackish waters. Members of this family occur in Africa, Asia, and North America, with extinct species known fromAustralia.[2] Most species have traditionally been included in the genusTrionyx, but the vast majority have since been moved to other genera. Among these are the North AmericanApalone softshells that were placed inTrionyx until 1987.[3]
Turtles of the family Trionychidae are called "softshell" because theircarapaces lack hornyscutes (scales), though the spiny softshell,Apalone spinifera, does have some scale-like projections, to which its common name refers. The carapace is leathery and pliable, particularly at the sides. The central part of the carapace has a layer of solid bone beneath it, as in other turtles, but this is absent at the outer edges. Some species also have dermal bones in theplastron, but these are not attached to the bones of the shell. The light and flexible shell of these turtles allows them to move more easily in open water or in muddy lake bottoms. Having a soft shell also allows them to move much faster on land than most turtles.[4] Their feet are webbed and three-clawed, hence the family name "Trionychidae," which means "three-clawed". The carapace color of each type of softshell turtle tends to match the sand or mud color of its geographical region, assisting in their "lie in wait" feeding methodology.
These turtles have many characteristics pertaining to their aquatic lifestyle. Many must be submerged in order to swallow their food.[5] They have elongated, soft,snorkel-like nostrils. Their necks are disproportionately long in comparison to their body sizes, enabling them to breathe surface air while their bodies remain submerged in the substrate (mud or sand) a foot or more below the surface.
Females can grow up to several feet in carapace diameter, while males stay much smaller; this is their main form ofsexual dimorphism.Pelochelys cantorii, found in southeastern Asia, is the largest softshell turtle.
Most are strict carnivores, with diets consisting mainly of fish, aquatic crustaceans, snails, amphibians,[4] and sometimes birds and small mammals.
Softshells are able to "breathe" underwater with rhythmic movements of their mouth cavity, which contains numerous processes copiously supplied with blood, acting similarly to gill filaments in fish.[6] This enables them to stay underwater for prolonged periods. Moreover, theChinese softshell turtle has been shown to excreteurea while "breathing" underwater; this is an efficient solution when the animal does not have access to fresh water, e.g., in brackish-water environments.[7]
According toDitmars (1910): "The mandibles of many species form the outer border of powerful crushing processes—the alveolar surfaces of the jaws", which aids the ingestion of tough prey such as molluscs. These jaws make large turtles dangerous, as they are capable of amputating a person's finger, or possibly their hand.[8]
Unlike thetemperature-dependent sex determination of most turtles, Trionychids haveZZ/ZW genetic sex determination;microchromosomes play a role in determining sex.[9]
Softshell turtles are eaten as adelicacy in most parts of their range, particularly in East Asia. A Chinese dishstews them withchicken. According to a 1930 report bySoame Jenyns,Guangdong restaurants had them imported fromGuangxi in large numbers; "eaten stewed with almonds, roast with chili sauce or fried with bamboo shoots, they [were] considered a great delicacy."[10]
Worldwide, the most commonly consumed softshell species is the Chinese softshellPelodiscus sinensis. As anoted Japanese biologist pointed out in 1904, the Japanese variety of this turtle, which at time was classified asTrionyx japonicus, occupied a place in Japanese cuisine as esteemed as thediamondback terrapin in the United States or thegreen turtle in England. Thefarming of this "luscious reptile", known in Japan assuppon, was already developed on an industrial scale in that country by the late 19th century.[11]
Due to rising demand and overhunting, the price ofPelodiscus sinensis in China skyrocketed by the mid-1990s; large-scaleturtle farming in China and neighboring countries; raising this species by hundreds of millions was the response, with prices soon returning to a more affordable level.[12][13][14] Another species,Palea steindachneri, is farmed in China, as well, but on a much smaller scale (with farm herds measured in hundreds of thousands, rather than hundreds of millions).[14]
In the United States, harvesting softshells (e.g.Apalone ferox) was, until recently, legal inFlorida. Environmental groups have been advocating the authorities' banning or restricting the practice. TheFlorida Fish and Wildlife Conservation Commission responded by introducing the daily limit of 20 turtles for licensed harvesters—a level which the turtle advocates consider unsustainable, as there may be between 100 and 500 hunters statewide. While some catch was consumed locally, most was exported; the Commission estimated (2008) around 3,000 pounds of softshell turtles were exported to China each week viaTampa International Airport.[15]
New rules, in effect as of July 20, 2009, restrict collecting any wild turtles to one turtle per person per day, completely prohibit collection of softshells (Apalone) in May through July, and prohibit trade in turtles caught from the wild. An exemption is provided for licensedturtle farms that need to catch turtles in the wild to serve as their breeding stock.[16]
Some other US states, too, have already adopted strict limitations on wild turtle trade. In 2009,South Carolina passed a law (Bill H.3121) restricting interstate and international export of wild-caught turtles (both soft-shell and some other species) to 10 turtles per person at one time, and 20 turtles per person per year.[17]
Family Trionychidae
The followingcladogram shows the relationships among the species:[19]
| Trionychidae | |
_Indian_flap_shell_Turtle_04.JPG)
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Trionychidae family | ||||
|---|---|---|---|---|
| ||||
| Genera |
|  | ||
| Amyda | ||||
| Apalone | ||||
| †Axestemys | ||||
| Chitra | ||||
| Cyclanorbis | ||||
| Cycloderma | ||||
| Dogania | ||||
| †Gilmoremys | ||||
| †Hutchemys | ||||
| †Khunnuchelys | ||||
| Lissemys | ||||
| Nilssonia | ||||
| †Palaeoamyda | ||||
| Palea | ||||
| Pelochelys | ||||
| Pelodiscus | ||||
| Rafetus | ||||
| Trionyx | ||||
Phylogenetic arrangement of turtles based onturtles of the world 2017 update: Annotated checklist and atlas of taxonomy, synonymy, distribution, and conservation status. †=extinct. | ||||