(Le Sueur, 1827)
Smooth softshell turtle
The round, smooth carapace (to 34.5 cm) is olive to orange brown, with a pattern of darker dots, dashes, or blotches; often there is a lighter marginal band bordered on the inside by a darker area. The leathery carapace lacks spines or raised knobs, and there is no marginal ridge. There is no preneural bone, and only a single neural separates the anterior pair of costal bones. Seven or eight neurals and seven or eight pairs of costals are present; the posterior costals may or may not meet at the midline. Carapacial bones are strongly pitted. The white or gray, patternless plastron has callosities on the hypoplastra and xiphiplastra, which seem larger than those in A. ferox or A. spinifera. Adults also frequently have callosities on the epiplastra and entoplastron; that on the entoplastron sometimes covers the entire surface. The entoplastron is not divided, and its median angle is obtuse and somewhat greater than 90° (Webb, 1962). The hyo- and hypoplastra may be fused, or may be connected by a suture. The moderately sized skull has a bony snout which is about as long as the greatest diameter of the orbit. The mandibular symphysis is shorter than the greatest diameter of the orbit. No medial ridge occurs on the maxilla. Head, neck, and limbs are olive to orangish above and gray to white below; there may be a few scattered dark spots on the limbs, but they are generally without a distinct pattern. A black-bordered light stripe extends through the eye and onto the neck. The tubular snout usually terminates somewhat obliquely, and the round nostrils are slightly inferior; no septal ridge is present.
Diploid chromosomes total 66, including 16 metacentric and submetacentric, 12 subtelocentric, and 38 acrocentric and telocentric chromosomes, with a total of 94 arms (Stock, 1972).
Adult males (11.0-17.5 cm) have long, thick tails with the vent near the tail tip. Females have longer hindclaws but males have longer foreclaws. Adult females (17.0-34.5 cm) may have a mottled or blotched carapace.
Apalone mutica ranges from Ohio, Minnesota, and North Dakota south to the western Florida Panhandle, southeastern Texas, and eastern New Mexico. It is now considered extirpated in western Pennsylvania.
Two subspecies are recognized. Apalone mutica mutica (Le Sueur, 1827), the Midland smooth softshell turtle, ranges in the central United States from Ohio to southern Minnesota and South Dakota, south to Tennessee, Louisiana, and Oklahoma and west into Texas and New Mexico. It is distinguished by a juvenile pattern of dusky dots and short lines, ill-defined pale stripes on the snout, and pale postocular stripes with black borders less than half their width, except in some individuals in the Colorado River drainage of Texas. The Gulf Coast smooth softshell turtle A. m. calvata (Webb, 1959) occurs along the Gulf coast from the Escambia River system of Alabama and the Florida Panhandle west to eastern Louisiana and Mississippi, including the Pearl River drainage. It has a juvenile pattern of large circular (often ocellate) carapacial spots, no stripes on the dorsal surface of the snout, a pattern of fine markings on the dorsal surface of the limbs, and pale postocular stripes having thick black borders approximately half their width on adult males.
The smooth softshell occurs in large rivers and streams having moderate to fast currents. A. m. calvata has been taken only from such habitats, but A. m. mutica is also known from lakes, impoundments, and shallow bogs. Waterways with sandy bottoms and a few rocks or aquatic plants are preferred.
Plummer (1977a) saw courtship behavior in April, May, June, and August. Males approached other basking turtles with neck fully extended and placed their snouts under the edge of the other turtle's carapace and probed around to the sides and back. If the other turtle was a female, she often would spin around, charge and bite at the male. Receptive females remained passive while the male investigated and mounted. Mountings were only successful in deeper water.
The nesting period lasts from late May through July. Nests are dug on sandbars, banks, and islands in full sunlight, and are 15-22 cm deep. Clutches consist of 3-33 eggs (11-22 are usual), and two to three clutches may be laid each season. Eggs are spherical (20-23 mm in diameter) with thick, brittle, white shells. Incubation lasts 65-77 days. The lower threshold for normal development of eggs is 25°C, and eggs in natural nests may experience short periods of high temperatures and survive, but more constant temperatures of about 36°C are lethal (Plummer et al., 1994).
The dull-olive carapace (34-45 mm) of the hatchling is marked with numerous short, black lines and bordered with a pale margin, which broadens posteriorly. Like adults, the young are nearly circular in outline.
Smooth softshells are decidedly carnivorous; some plant material is eaten, however, perhaps accidentally. They obtain food by prowling about on the bottom or on submerged debris, actively pursuing and capturing prey, or by ambushing it by lying concealed on the bottom. Apalone mutica feeds on fish, frogs, tadpoles, mudpuppies (Necturus), crayfish, aquatic insects, snails, bivalves, and worms. Plant material reportedly taken includes algae, fruits, and "hard nuts" (Carr, 1952). Captives feed readily on canned or fresh fish and various meats.
IUCN Red List Status (1996)