Order Testudines
Suborder Cryptodira
Superfamily Trionychoidea

Family Trionychidae - Softshell Turtles

Content: 3 subfamilies: Cyclanorbinae, Trionychinae, ca. 25 species

Appearance and morphology: Softshells are flattened, pancake-shaped turtles that have reduced bony carapaces and plastrons. The carapace and plastron are naked, lacking epidermal scutes, but are covered with a thick, leathery skin. The jaw closure mechanism articulates on a trochlear surface of the otic capsule and is enclosed in a synovial capsule. An epipterygoid is present in the skull; the internal carotid canal lies in the pterygoid, and the parietal but not the postorbital touches the squamosal. The facial nerve lacks a hyomandibular branch. The plastron lacks a mesoplastron, and the plastral buttresses do not form (?); the flattened carapace lacks peripheral bones (except in Lissemys), and the nuchal lacks costiform processes. The neck withdraws vertically, and this mechanism is reflected in an anteroventrally oriented articular surface of the first thoracic vertebra; other vertebral traits are the exclusion of the 10th thoracic vertebra from the sacral complex and procoelous caudal vertebrae. The pelvic girdle flexibly articulates with the plastron, and the ilium has a thelial process (after Zug et al. 2001).

Characteristic differences between the subfamilies:

Cyclanorbinae have a latticelike plastral skeleton with bilaterally fused hyoplastral and hypoplastral bones. Externally the plastron has well-developed femoral flaps. Trionychinae also have a latticelike plastral skeleton but with separate hyoplastral and hypoplastral bones on each side. The plastron lacks femoral flaps.

Size: Cyclanorbinae: 37 cm (Lissemys) to 60 cm (Cyclanorbis elegans) carapace length. Trionychinae: 20 cm (Pelodiscus sinensis) to more than 1 m (Trionyx triunguis, Pelochelys, Chitra); most other genera reach 40 to 60 cm carapace length.

Distribution: Sub-Saharan and northeastern central Africa, South Asia (Cyclanorbinae); Eastern North America, South Asia to Japan and southward to New Guinea, north-central sub-Saharan Africa into Southwest Asia (Trionychinae).

Habitat: All cyclanorbines are probably aquatic bottom-dwellers like trionychines and both live in rivers and lakes. Dogania subplana occurs in small mountain streams

Behavior: Softshells actively forage and also lie partially hidden in the bottom sand or silt, waiting for passing prey. Their long necks and snorkellike snouts permit them to stick their noses to the water surface to breathe. At least trionychines may also depend on cutaneous respiration. Trionychines are actively foraging for prey and they are excellent swimmers.

Reproduction: Lissemys punctata deposits 2 to 14 eggs. Clutch size may vary geographically and at least some females produce multiple clutches per year. Incubation ranges from 30 to 40 days to more than 300 days in some cyclanorbines. Temperate and subtemperate trionychines are predominantly spring breeders and tropical species lay eggs in the early dry season. apalone deposits 4 to 30 eggs per clutch while Pelodiscus sinensis lays 9 to 15 eggs. The large Trionyx triunguis can deposit over 100 eggs but usually produces about 50. Incubation is generally 56 to 70 days, although in Aspideretes gangeticus it lasts 250 to 290 days. The lower record is hold by Pelodiscus sinensis with an incubation period of 28 days.

Food: Cyclanorbinae: invertebrates, small vertebrates, occasionally plants. Trionychinae are predominantly carnivorous although the may eat plant material if animal prey is not available.

Taxonomic note: Wermuth & Mertens (1977) listed 11 species of the genus Trionyx. Ernst & Barbour (1989) split this group in many separate genera. According to Engstrom et al. (2004) Nilssonia is nested within Aspideretes but the former has priority over the latter, i.e. all Aspideretes should be renamed Nilssonia.

Subfamilia Cyclanorbinae

• Cyclanorbis
• Cycloderma
• Lissemys

Subfamilia Trionychinae

• Amyda
• Apalone
• Chitra
• Dogania
• Nilssonia (incl. Aspideretes)
• Palea
• Pelochelys
• Pelodiscus
• Rafetus
• Trionyx

Click on genus to get a list of species. Use the Search form for more sophisticated searches (HELP on Search).

References:

Engstrom, Tag N., H. Bradley Shaffer, and William P. McCord. 2002
Phylogenetic Diversity of Endangered and Critically Endangered Southeast Asian Softshell Turtles (Trionychidae: Chitra).
Biological Conservation 104 (2):173-179

Engstrom, Tag N., H. Bradley Shaffer, and William P. McCord (2004)
Multiple Data Sets, High Homoplasy, and the Phylogeny of Softshell Turtles (Testudines: Trionychidae).
Syst. Biol. 53 (5): 693-710

Ernst,C.H. & Barbour,R.W. (1989)
Turtles of the World
Smithsonian Institution Press, Washington D.C. - London

Meylan, P.A. 1987
The phylogenetic relationships of soft-shelled turtles (Family Trionychidae).
Bulletin of the American Museum of Natural History 186 (1):1-101.

Praschag, P.; Hundsdörfer, A.K.; Reza, A.H.M.A. & Fritz, U. 2007
Genetic evidence for wild-living Aspideretes nigricans and a molecular phylogeny of South Asian softshell turtles (Reptilia: Trionychidae: Aspideretes, Nilssonia).
Zoologica Scripta 36 (4): 301-310

Webb R G 1990
Trionyx Geoffroy Saint-Hilaire. Softshell turtles.
Catalogue of American Amphibians and Reptiles 487: 1-7

Weisrock,D.W. & Janzen,F.J. 2000
Comparative molecular phylogeography of North American Softshell Turtles (Apalone): implication for regional and wide-scale historical evolutionary forces.
Mol. Phylogenet. Evol. 14 (1): 152-164

Wermuth,H. & Mertens,R. (1977)
Liste der rezenten Amphibien und Reptilien:
Testudines, Crocodylia, Rhynchocephalia
Das Tierreich, Lfg. 100, XXVII + 174 pp.
Walter de Gruyter, Berlin-New York

Zug,G.R.; Vitt, L.J. & Caldwell, J.P. (2001)
Herpetology, 2nd ed.
Academic Press San Diego, London, [...]XIV + 630 pp.

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