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.
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