Trionychidae

(vertebrate zoology) The soft-shelled turtles, a family of reptiles in the order Chelonia.

(Trionychidae)

Class: Reptilia

Order: Testudines

Suborder: Cryptodira

Family: Trionychidae

Thumbnail description
Medium to very large aquatic turtles with a rounded, flattened carapace covered with leathery skin; fleshy skin on the head that covers the jaws; and streamlined forelimbs with three pronounced claws

Size
4–47 in (10–120 cm)

Number of genera, species
13 genera; 25 species

Habitat
Rivers, streams, lakes, marshes, and temporary ponds

Conservation status
Critically Endangered: 5 species; Endangered: 5 species; Vulnerable: 6 species

Distribution
North America, Africa, Asia, Indo-Australian archipelago

Evolution and systematics

These primitive cryptodires are most closely related to the Carettochelyidae of New Guinea and Australia. The oldest softshell fossil is from the late Jurassic. The recent revision of the phylogenetic arrangement proposed by Meylan has yet to gain universal acceptance and use, but it is generally supported by both morphological and molecular evidence. Two subfamilies are recognized: Trionychinae (without flexible flaps on plastron below hind limbs) and Cyclanorbinae (with flexible flaps on plastron below hind limbs).

Physical characteristics

Softshell turtles gain their name from the leathery layer of epidermis that covers the bony portion of the carapace and extends, in most species, to form a flexible disk overhanging the feet and tail. Flap-shelled species have a limited leathery carapace; however, they have developed retractable, flaplike hinges on the plastron that protect the limbs from below. When considering the entire leathery shell, the diversity of sizes found among softshell species covers an order of magnitude in carapace length. The smallest species attains a maximum size of 5 in (12 cm), whereas adults of the largest species may reach 47 in (120 cm) or more.

Most species possess a long retractile neck; this is especially well developed in the giant ambush-feeding species. However, the head of the Malayan softshell (Dogania subplana) is too large to be drawn completely within the shell. The long, tubelike proboscis found in most species allows them to breathe air from the water's surface without moving from the bottom. A thick layer of fleshy skin covers an incredibly sharp horny beak. The digits are strongly webbed with three claws present on each of the forelimbs. Most species are fairly uniform in coloration, allowing them to blend in with the substrate; however, several species in India and Southeast Asia have unique patterns on the carapace that may consist of broad stripes, vibrant spots, or elaborate designs. The plastron may exhibit two to nine callosities—thickened areas of epidermis overlying the plastral bones that develop as the turtle grows. Plastral callosities vary in number and shape among species and, when comparing adults, may be useful in taxonomic identification.

Distribution

Softshell turtles are found in lowland temperate regions east of the Rocky Mountains of North America, in sub-Saharan Africa and along the Nile River into Egypt, and across the Mediterranean Sea to southern Turkey and the Middle East. They also are present from eastern Pakistan, throughout India and southern Asia along the coast of China into southeastern Russia, and throughout the Indo-Australian archipelago to the southern shores of Irian Jaya, but there are no living species in Australia. The Malayan softshell (Dogania subplana) is the only species known to inhabit streams at high elevations. Trionychids formerly were distributed throughout Europe, South America, and Australia, as well as the three continents where they occur today. The Chinese softshells (Pelodiscus sinensis, Palea steindachneri) have been established by accidental or intentional introductions outside the known range. Extralimital populations of both species, farmed throughout Southeast Asia, have been documented in the Hawaiian Islands.

Habitat

These highly aquatic turtles may be found in all freshwater habitats. Most species prefer clean, well-oxygenated waterways with soft sand or mud bottoms. They commonly inhabit large rivers, streams, lakes, and ponds, but they also may occur in swamps, marshes, temporary ponds, and drainage ditches. A few species tolerate brackish water, but only the Asian giant softshell (Pelochelys cantorii) is a permanent resident of coastal waters.

Behavior

Softshell turtles may remain buried at the bottom of their aquatic habitat for most of the day; however, some species will bask on sandbars or steep riverbanks. Prolonged submergence is possible because they can absorb oxygen across the skin and lining of the throat. This is especially important for temperate species that hibernate for months beneath the ice. Conversely, the flap-shelled turtles may be adapted to long periods of drought. The protective shell enables these turtles to burrow deep into the mud and may prevent desiccation while estivating.

Feeding ecology and diet

Most species are primarily carnivorous; however, plant material may occasionally be consumed. The majority of softshell species are generalists; all forms of animal matter (live or as carrion) are taken opportunistically. A few species are highly specialized for ambushing fish and other free-swimming aquatic animals. Adaptations for this mode of prey acquisition are most highly developed in the Asian narrow-headed softshell (Chitra indica); these turtles have small, forward-set eyes and exceptionally long necks that can be thrust from the sandy bottom with explosive speed and deadly accuracy.

Reproductive biology

Mating generally occurs in the spring; however, some species may store sperm for several years. The spherical eggs are generally laid in sandy banks above the flood line along a river or lake. Clutch size ranges from as few as 3 eggs in some species to more than 100 in others. Some species lay several clutches in a single year. Most species that have been investigated exhibit genetic sex determination; however, heteromorphic sex chromosomes are not present.

Conservation status

Six species are listed as Vulnerable, five as Endangered, and five as Critically Endangered on the IUCN Red List. As with most turtle species endemic to Asia, the softshells of China, Southeast Asia, and India are heavily exploited for food and medicine. Most softshells are dependent upon high levels of dissolved oxygen in their aquatic environment; therefore, they are particularly vulnerable to the effects of habitat destruction and degradation. They are extremely sensitive to rotenone, a chemical that is intentionally added to streams to kill fish, and pesticides (e.g., DDT) in farmland runoff. Human consumption has taken a heavy toll on the populations of many Asian species. Many species are legally protected by local countries, but exploitation continues. Some species are used to meet the demands of food markets.

Significance to humans

Softshells are used for food throughout their range; however, Pelodiscus sinensis is intensively farmed throughout Asia to supply consumer demand in China.

Species accounts

Resources

Das, Indraneil. Die Schildkröten des Indischen Subkontinents. Frankfurt, Germany: Chimaira, 2001.

Greenbaum, E., and J. L. Carr. "Sexual Differentiation in the Spiny Softshell Turtle (Apalone spinifera), a Turtle with Genetic Sex Determination." Journal of Experimental Zoology 290 (2001): 190–200.

Meylan, Peter A. "Phylogenetic Relationships of Soft-Shelled Turtles (Family: Trionychidae)." Bulletin of the American Museum of Natural History 186 (1987): 1–101.

Pritchard, Peter C. H. "Observations on Body Size, Sympatry, and Niche Divergence in Softshell Turtles (Trionychidae)." Chelonian Conservation and Biology 4 (2001): 5–27.

[Article by: Patrick J. Baker, MS]

The noun has one meaning:

Meaning #1: soft-shelled turtles
  Synonym: family Trionychidae

Trionychidae
Chinese Softshelled Turtle Pelodiscus sinensis
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Subclass:	Anapsida
Order:	Testudines
Suborder:	Cryptodira
Superfamily:	Trionychoidea
Family:	Trionychidae Fitzinger, 1826
Subfamilies
Cyclanorbinae Trionychinae

Trionychidae is a taxonomic family which comprises a number of turtle genera commonly known as soft-shell turtles. It consists of some of the world's largest fresh water turtles, though many can adapt to living in highly brackish areas. Members of this family occur in Africa, Asia, North America, and Southeast Asia. North American members of genus Trionyx were fairly recently^[when?] assigned the new genus name Apalone, though they are still listed semi-correctly as Trionyx in some texts.

Contents 1 Characteristics 2 Soft-shell turtles as food 3 Taxonomy 4 Notes 5 References

Characteristics

They are called "soft shelled" because their carapace lacks horny scutes (scales), though the Spiny Softshell Turtle, Apalone spinifera, does have some scale-like projections, hence its name. 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 the plastron, 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.^[1]

Females can grow up to several feet in carapace diameter, while males stay much smaller; this is their main form of sexual dimorphism. Pelochelys cantorii, found in southeastern Asia, is the largest softshell turtle on earth.

Head and neck of Pelodiscus sinensis.

These turtles have many characteristics pertaining to their aquatic lifestyle. Like all aquatic turtles, they need to be submerged to be able to swallow food. Most are strict carnivores, with diets consisting mainly of fishes, aquatic crustaceans, snails, amphibians,^[1] and sometimes birds and small mammals. They have elongated, soft, snorkel-like nostrils. Their necks are disproportionately long in comparison to their body size, enabling them to breathe surface air while their bodies remain submerged in the substrate (mud or sand) a foot or more below the surface.

Like some amphibians and marine snakes, softshell turtles are able to extract a small amount of oxygen out of water via their skin, further enabling them to stay underwater for prolonged periods.^[2] Their feet are webbed and are three-clawed, hence the "Tri-" in the genus name. The carapace color of each type of softshell turtle tends to match the sand and/or mud color of its geographical region, assisting in their "lie and wait" feeding methodology.

Soft-Shelled Turtles look rather helpless but are fully able to protect them-selves in time of danger. "Hidden by the lips, are a pair of mandibles remarkably keen and strong; on many specimens the mandibles form the outer border of powerful crushing processes- the alveolar surfaces of the jaws; examples thus provided feed largely on mollusks. Taken at a disadvantage, out of the water, the soft-shelled turtles are savage fighters. the head darts at an offending object like that of a snake. Large turtles are dangerous; for they can amputate a man's finger- possibly his hand."^[3]

Soft-shell turtles as food

Japanese Suppon-nabe made from Trionychidae

In a Seoul market

Soft-shell turtles are eaten as a delicacy in most parts of their range, particularly in East Asia. Chinese people, in particular, enjoy eating them with chicken in stew.

In the United States, "harvesting" them is legal in Florida. Environmental groups have been advocating with the authorities for banning, or restricting, the practice. The Florida Fish and Wildlife Conservation Commission responded by introducing the daily limit of 20 turtles per day for licensed harvesters - the level which the turtles advocates consider unsustainable, as there may be anywhere between 100 to 500 hunters state-wide. While some catch is consumed locally, most is exported; the Commission estimates (2008) that around 3,000 pounds of softshell turtles are exported each week via Tampa International Airport.^[4]

After meetings and discussions with a diverse group of stakeholders, Commission staff decided to propose a ban on commercial take of freshwater turtles. Further study revealed there is a potential for a commercial market to impact freshwater turtle populations through too much harvest pressure, which in turn could threaten the sustainability and the unique diversity of turtles in Florida.

Because of these potential threats, the Commission staff believes substantial monitoring would need to be conducted and data collected if commercial harvest of turtles continued. This process would be difficult and expensive. The Commission has no feasible cost-effective process for developing a monitoring program that would allow a sustainable commercial harvest. Commission staff believes an effective way to ensure sustainability of turtles is through highly restrictive conservation measures. Commissioners directed staff to finalize a draft rule that bans the commercial take or sale of wild freshwater turtles.

Taxonomy

Family Trionychidae

• Palaeotrionyx (extinct)
• Subfamily Cyclanorbinae
  • Genus Cyclanorbis
  • Genus Cycloderma
  • Genus Lissemys
• Subfamily Trionychinae
  • Genus Amyda
  • Genus Apalone
  • Genus Aspideretes (might belong in Nilssonia)
  • Genus Chitra
  • Genus Dogania
  • Genus Nilssonia
  • Genus Palea
  • Genus Pelochelys
  • Genus Pelodiscus
  • Genus Rafetus
  • Genus Trionyx

Notes

1. ^ ^{a b} Obst, Fritz Jurgen (1998). Cogger, H.G. & Zweifel, R.G.. ed. Encyclopedia of Reptiles and Amphibians. San Diego: Academic Press. pp. 117–118. ISBN 0-12-178560-2. 
2. ^ King, Peter and Harold Heatwole (1994) Partitioning of Aquatic Oxygen Uptake among Different Respiratory Surfaces in a Freely Diving Pleurodiran Turtle, Elseya latisternum. Copeia, 3:802-806
3. ^ Ditmars
4. ^ "China Gobbling Up Florida Turtles", By CRAIG PITTMAN, St. Petersburg Times. Published: Thursday, October 9, 2008

References

Wikimedia Commons has media related to: Trionychidae

• The Reptile Database: Family Trionychidae

Parade of the Animal Kingdom. Hegner, Robert. 1935. the Macmillan Company.

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