Systematics: Originally described as Trionyx spiniferus by Charles Alexander LeSueur in 1827, based on a specimen from the Wabash River, Posey County, Indiana. The nomenclatural history of this species in the Virginia literature is convoluted. Hoffman (1949b) used Trionyx spinifera, following Stejneger and Barbour (1943). Burger (1958) used Amydaferox spinifera, following Conant and Goin (1948). Conant (1958) and Jopson (1972) used Trionyx spinifer, following Schwartz (1956a). Most authors after Webb (1962, 1973) used the original combination, Trionyx spiniferus, including those in the Virginia literature (e.g., Conant, 1975; Mitchell, 1976a, 1981a; Tobey, 1985). Recently, a systematic analysis of softshell turtles worldwide (Meylan, 1987) suggested that the spiny softshell required another generic name to reflect the known hierarchical relationships within the group. For North American softshells, Meylan resurrected the genus Apalone, first used by Rafinesque (1832) for the spiny softshell, although Rafinesque thought at that time he had a new species, which he called Apalone hudsonica. Most recent authors have used the combination A. spinifera (e.g., Ernst and Barbour, 1989a; Conant and Collins, 1991; Mitchell, 1991a; Iverson, 1992), although it is not universally accepted (Webb, 1990).

Content follows McGaugh et al. (2008, Zoologica Scripta 37: 289–304), who synonymized A. s. hartwegi with A. s. spinifera.

Description: A large freshwater turtle reaching a maximum carapace length (CL) of 457 mm (18.0 inches) (Ernst and Barbour, 1972). In Virginia, maximum known CL is 250 mm and maximum plastron length (PL) is 159 mm.

Morphology: Carapace flattened, round, keelless, and leathery; epidermal plates (scutes) absent; surface texture of carapace sandpaper-like; anterior edge of carapace bears a number of spinelike tubercles; posterior carapace flexible; hingeless plastron small (64-73% of CL); head elongated; snout elongated with large nostrils, each of which contains a ridge that projects from septum; jaws with sharp cutting edges; neck elongated, about two-thirds of CL; feet strongly webbed; 3 claws on forefeet and 4 on hindfeet.

Coloration and Pattern: Carapace olive to brown with a variable number of thin-lined, black hollow circles or irregular black blotches; single black line (may be broken) along inside margin of carapace, except anteriorly; plastron white or yellowish; 2 yellowish lines on each side of head; margins of jaws cream to yellowish; skin gray to olive with a peppering of small black dots.

Sexual Dimorphism: Sexual size dimorphism is characteristic of this turtle. Adult females were larger (165-457 mm CL) than males (127-216 mm CL) (Ernst and Barbour, 1972). .Adult males averaged 150.0 ± 32.0 mm CL (127.2-205.0, n = 5), 106.1 ±22.8 mm PL (88.7-145.0), and 462.7 ± 28.2 g body mass (313-788, n = 3). The only known adult female from Virginia was 250 mm CL and159 mm PL. Sexual dimorphism index in midwestern populations was 0.62-0.67 (Gibbons and Lovich, 1990, as modified by Lovich and Gibbons, 1992). The anal opening of males is near the tip of the tail; it extends well past the carapace. In females, the anal opening is at the base of the tail and does not extend beyond the posterior carapacial margin. Males retain the pattern of hollow spots characteristic of juveniles. The pattern in females changes to dark-brown or black irregular blotches or mottling.

Juveniles: Juveniles are strongly patterned, with small black dots and hollow black circles on a light-tan or olive carapace. The inside carapacial margin is yellow and bordered by a single thin black line. Juveniles are somewhat smoother than adults and the spines on the anterior carapace are reduced. Hatchlings were 30-40 mm CL (Ernst and Barbour, 1972). No hatchlings are known from Virginia.

Confusing Species: No other Virginia turtle can be confused with this species because of its long snout and leathery shell. At a distance, softshells can be distinguished (with binoculars) from Graptemys geographica and Trachemys scripta by head shape and the flat shell. Map Turtles and Sliders have rounded snouts on shorter necks and raised shells. Snapping Turtles (Chelydra serpentina) have large heads with rounded snouts, long tails with dorsal projections, and shells with distinct scutes and projections along the posterior margin.

Geographic Variation: None known in Virginia.

Biology: Softshell Turtles are highly aquatic and seldom venture out of the water. In Virginia, they are almost entirely confined to rivers and some of their tributaries, but may occupy quarry ponds and nearby farm ponds. Preferred habitat appears to be correlated with sandy to soft organic substrate, some aquatic vegetation, and basking sites near deep water. Sandbars in areas with these characteristics are good indicators of softshell habitat. Softshells in Tennessee, and presumably Virginia, are active from April through October (Robinson and Murphy, 1978). All known Virginia specimens were caught in June (3) and August (4). These turtles overwinter in several centimeters of mud in deep water. They are able to obtain oxygen from the oxygen-rich cold water across membranes in the cloaca and across the skin. Dunson (1960) found that softshells could stay submerged in oxygen-poor warm water for up to 5 hours.

Apalone spinifera is carnivorous at all ages. Prey recorded from other parts of its range are adult and larval aquatic insects, crayfish, and fish (Lagler, 1943; Ernst and Barbour, 1972). In a Minnesota study of A. spinifera prey, Cochran and McConville (1983) found aquatic larvae of mayflies, caddisflies, dragonflies, damselflies, flies (Diptera), and beetles; pupae and larvae of terrestrial lepidopterans; water beetles; crayfish; isopods; worms; mussels; snails (or slugs); white crappie (Pomoxis annularis) fingerlings (possibly taken in trap); and vegetation fragments. One Virginia turtle contained crayfish parts and unidentified vegetation in its feces. Adults have few predators other than humans. Juveniles are eaten by large fish, Snapping Turtles (Chelydra serpentina), and large wading birds (Ernst and Barbour, 1972). Eggs in nests are probably eaten by raccoons (Procyon lotor) and skunks (Mephitis, Spilogale).

Reproduction in this species has been studied in middle Tennessee by Robinson and Murphy (1978). Males matured at about 112 mm CL, 80 mm PL, and 133 g body mass. The smallest male from Virginia that appeared to be mature was 127.2 mm CL and 88.7 mm PL. The testicular and spermatogenic cycle follows that described for other Virginia turtles (Mitchell, 1985a, 1985c), with minimum testis size and cellular activity in spring, and peak size and production of sperm in August. Robinson and Murphy (1978) found that females matured at about 285 mm CL, 191 mm PL, and 1,400-1,500 g body mass. The only known mature female from Virginia (USNM 101386) was 250 mm CL and 159 mm PL. The female reproductive cycle follows the pattern for other Virginia turtles (Mitchell, 1985b, 1985d), with ovarian size smallest in August, growth of follicles in fall and spring, and egg laying in June and July. Clutch size through out the range of this species was 4-32 eggs (Ernst and Barbour, 1972). Robinson and Murphy (1978) reported evidence for two clutches a season in some females. The single Virginia female contained 26 oviductal eggs (27 mm in diameter) and 16 enlarged (16-17 mm) follicles. In the midwest, the natural incubation period is 82-84 days and hatching occurs in late August to October (Ewert, 1979).

The population ecology of this species has not been studied.

Softshell turtles frequently bask on rocks and logs near deep water. These turtles will often rest on the substrate in water shallow enough to allow them to reach the surface to breathe. They will bury themselves by flipping sand or silt over the shell and by shimmying down into the substrate, rendering them completely camouflaged. Prey are ambushed from this position. These turtles bite and scratch badly when caught, but catching them is difficult because they are quick and the flexible shell is slippery.

Remarks: This is one of the most poorly known turtles in Virginia. All newly acquired information on the biology of this species should be published.

Conservation and Management: This species is listed as status undetermined by Mitchell and Pague (1987) and Mitchell (1991a) because of the paucity of information on its population biology in Virginia. Because it is an almost entirely aquatic turtle, it may be susceptible to chemical pollution. It can certainly accumulate pollutants via its prey. The population ecology and distribution of this turtle need to be studied. The river systems in the Tennessee drainage need to be monitored for contamination, and the conservation of this entire area in Virginia should be the focus of much attention.