Systematics: Originally described as Goniochelys minor by Louis Agassiz in 1857 from specimens he saw from Alabama, Georgia, and Louisiana. Schmidt (1953) restricted the type locality to Columbus, Georgia. Stejneger (1923) discussed why it had not been recognized as a species for many years and placed it in the genus Sternotherus. The spelling of the generic name is discussed in "Remarks." Seidel et al. (1986) and Iverson (1991) suggested that the genus Sternotherus was more appropriately considered a subgenus of Kinostemon, but this relationship has not been universally accepted or clarified. Two subspecies are recognized: S. m. minor (Agassiz) and S. m. peltifer Smith and Glass. Their distributions were illustrated in Conant and Collins (1991). Sternotherus m. peltifer, which occurs in Virginia, was first described as Sternotherus peltifer by Smith and Glass (1947); the type locality is in Jefferson Davis County, Mississippi. Carr (1952) considered it a subspecies of S. carinatus. In the Virginia literature, only Burger (1958) used S. carinatus peltifer. After examining the relationships of several species in the genus Sternotherus, Tinkle and Webb (1955) determined peltifer to be a subspecies of S. minor. All Virginia authors have used Sternotherus minor peltifer. The monophyly of the genus Sternotherus was questioned by Seidel et al. (1986, Copeia 1986: 285–294) and Iverson (1991, Herpetol. Monogr. 5: 1–27); however, Iverson (1998, Chelon. Conserv. Biol. 3: 113–117) and Iverson et al. (2013, Mol. Phylogenet. Evol. 69: 929–939) provided support for its monophyly.

Description: A small aquatic turtle reaching a maximum carapace length (CL) of 135 mm (5.3 inches) (Iverson, 1977a). In Virginia, known maximum CL is 115.6 mm, maximum plastron length (PL) is 91.7 mm, and maximum body mass is 203 g.

Morphology: Carapace strongly arched and each vertebral scute slightly overlaps the one behind it; anterior vertebral scute is daggerlike, and widest points on anterior edge do not extend beyond middle of 1st marginals; marginals yellowish along edges dorsally and ventrally; marginals 11/11, pleurals 4/4, and vertebrals 5; 10th and 11th marginals on each side counting anterior to posterior are larger than the rest; narrow bridge consists only of small axillary and inguinal scutes; plastron 63-79% of CL; pectoral scute squarish in shape; plastral scutes reduced in size, allowing a variable amount of white skin to be exposed along midline; plastron with a weakly developed hinge that allows forelobe limited movement; 1 pair of barbels on chin; head large

Coloration and Pattern: Carapace brown to olive brown, with or without small, nondistinct black spots; seams of carapacial scutes thinly bordered by black; plastron yellowish with irregular black or dark-brown blotches on scutes; skin brown to gray-brown with gray to yellow mottling on legs; dorsum of head brown with black speckling; neck patterned with numerous alternating yellowish and black to dark-brown stripes; surfaces of jaws tan with black streaks or smudges; beak of lower jaw curved upward.

Sexual Dimorphism: Adult males averaged 88.1 ± 10.8 mm CL (68.6-98.5, n = 9), 60.9 ± 8.1 mm PL (45.0-68.5), and 99.2 ± 30.0 g body mass (52- 140). Adult females averaged 100.1 ± 10.2 mm CL (85.8-115.6, n = 7), 76.7 ± 8.0 mm PL (67.5-91.7), and 137.3 ± 36.0 g body mass (100-203, n = 6). Sexual dimorphism index was 0.14. The anal opening extends beyond the edge of the carapace (precloacal distance 12-24 mm, ave. = 17.3 ± 4.5, n = 6) in males but not in females (precloacal distance 7-11 mm, ave. = 9.3 ± 2.1, n = 3). Mature males have a spine on the terminal end of the tail and a patch of raised scales behind the knee on each rear leg.

Juveniles: Juveniles are similar to adults in pattern but have a single pronounced keel on the carapace. The single Virginia hatchling was 25.0 mm CL and 17.0 mm PL, and weighed 3.2 g. At hatching, the carapace is brown with dark-brown spots on the pleural scutes. The carapacial scutes are thinly outlined in black and the ventral side of all the marginals is orange. The plastron is orange and patternless.

Confusing Species: The only species that may be confused with S. minor peltifer in its Virginia range is Sternotherus odoratus, which has a dark-brown carapace, 2 distinct yellow lines on either side of the black to dark-brown head, a pair of barbels on the chin and a pair on the neck. The 1st vertebral scute is triangular and squared off at the posterior end. Juvenile Eastern Musk Turtles have 3 keels on the carapace and yellow to cream plastrons with black smudges.

Geographic Variation: None known in Virginia.

Biology: This is a completely aquatic turtle that is restricted to rivers and their tributaries. Tinkle (1958) noted that this species is "associated with running water or with permanent bodies of water connected with running water, such as oxbow lakes." It is rarely found in farm ponds and other isolated waters (Mount, 1975). Ernst and Barbour (1972) said that this turtle occurs commonly around snags and fallen trees and prefers a soft substrate. In Virginia, S. minor occurs in areas with aquatic and overhanging vegetation, rock cover, and soft substrates. The normal activity season in Virginia is unknown; all observations are May through August. Presumably, overwintering occurs under banks and in muskrat burrows.

Sternotherus minor is carnivorous but may take plant material on occasion. The freshwater mollusks Oxytrema simplex and Pleurocera unciale and the remains of a large beetle were found in the feces of one individual. Folkerts (1968) found the following prey in an Alabama sample: algae, aquatic plants, mollusks (mostly Oxytrema), crustaceans, adults and larvae of beetles, true bugs, mayflies, odonates, stoneflies, larvae of caddisflies, neuropterans, adult flies, and spiders. He observed adults biting clumps of algae covered with small snails. Freshwater mollusks (69.5%) and insects (15.6%) comprised the bulk of the diet. Tinkle (1958) added crayfish and fish (carrion?). As these turtles grow, they develop expanded crushing surfaces in both jaws and enlarged jaw muscles; this is apparently in response to crushing mollusk shells. Nothing is known of the predators of this species, but presumably large fish and Snapping Turtles (Chelydra serpentina) eat them, especially juveniles, in the water; raccoons (Procyon lotor) and skunks (Mephitis, Spilogale) prey on the eggs in nests. Those hooked on fishing lines are often beheaded by humans.

Almost nothing is known of the reproduction of S. minor peltifer compared to S. m. minor. Mating, which has not been described, probably occurs in spring and fall months. One female with two oviductal eggs was captured on 18 June 1987. She also contained three corpora lutea, indicating one egg was laid before capture. Presumably, nesting occurs mid-May into July, as in other turtles in this region. Size at maturity for a composite sample from throughout the species' range was 60 mm CL for males (3-4 years old) and 90 mm for females (6-8 years old) (Tinkle, 1958). Iverson (1978a) found that females matured at 60 mm PL (about 80 mm CL) in a Florida population. Clutch size in S. m. minor from Florida is one to five (Cox and Marion, 1978; Iverson, 1978). In Virginia, egg size of S. m. peltifer was 29.3 x 16.8 mm (length 28.1-30.4, width 16.3-17.3, n = 2); they averaged 4.9 g, well within the values reported by Cox and Marion (1978) and Iverson (1978a). Incubation time was 84 days and hatching occurred on 14 September.

The population ecology of this turtle has not been studied. Tinkle (1958) provided some information based on samples collected over several years from the entire range of S. minor peltifer. Sex ratio was 1.1 males to 1 female and density was 1 turtle to 17-25 m of river bank in an Alabama river.

This species seldom basks, but Ernst and Barbour (1972) noted that they are adept climbers and occasionally perch on overhanging limbs. I found one large (old?) female sitting on a root of a large tree on the river bank in shade; she appeared to be sick, as a large soft spot occurred on the carapace. This species can remain submerged for long periods of time (months) at 22°C because of its ability to obtain oxygen from the water via the moist lining of the mouth and throat (Belkin, 1968).

Remarks: The spelling of the former generic name of musk turtles in the Virginia literature has variously been Sternotherus (e.g., Hoffman, 1945a; Burger, 1958; Mitchell, 1976a, 1985b, 1985d, 1988) or Sternothaerus (e.g., Conant, 1958; Hardy, 1972; Jopson, 1972; Klimkiewicz, 1972). Zug (1971) reviewed the nomenclatural history and pointed out that the oldest published name is Sternotherus.

Conservation and Management: This is one of several freshwater turtles that occur in the upper Tennessee drainage system in south western Virginia. Little is known about any of these turtles in Virginia. The completely aquatic habits of this species leave it vulnerable to some forms of toxic chemical contamination. Its reliance on mollusk prey makes it a secondary target of pollution effects on mollusk populations. The fly ash spill in the Clinch River in the 1970s undoubtedly eliminated this species in many areas because of the nearly complete elimination of the molluscan fauna. The population ecology of this species needs to be studied to identify the vulnerable stages of its life history and to determine how it responds to changing environmental conditions.