(Garman, 1891)
Striped mud turtle
Recognition
This small (to 12 cm) mud turtle has a broad, smooth carapace which is keelless and unserrated in adults, and usually widest and highest behind the middle. A middorsal keel is present in juveniles. The 1st vertebral is elongated but widened anteriorly so that it extends to the seam separating the 1st and 2nd marginals on each side. Vertebrals 2-5 are usually broader than long. The vertebrals may be depressed, forming a broad, shallow middorsal groove. Marginal 10 is more elevated than the rest. The carapace varies from tan to black; some have rather transparent scutes; three variable light-yellow or cream-colored longitudinal stripes are usually present. The double-hinged plastron is broad and only slightly notched posteriorly. Its hindlobe is larger than the forelobe, and the abdominal scute is almost as long as the forelobe. The plastral formula is: an > abd > hum > gul > fem > pect. Axillary and inguinal scutes meet on the bridge. The plastron is olive to yellow and either plain or with dark seam borders. The small, conical head has a slightly protruding snout and a nonhooked upper jaw. Its rostral scale is, at best, only slightly posteriorly furcated. Two light stripes extend posteriorly from the orbit, one above and one below the tympanum. All skin is tan to black, and the neck and head may show dark mottling. A horny spine occurs at the tip of the tail.
The diploid chromosome number is 56 (Killebrew, 1975b; Sites et al., 1979; Bickham and Carr, 1983). According to Killebrew (1975b), Kinosternon baurii has 26 macrochromosomes and 30 microchromosomes, but Sites et al. (1979b) reported 24 macrochromosomes (12 metacentric or submetacentric, 12 telocentric or subtelocentric) and 32 microchromosomes.
Males have longer, thicker tails and a patch of rough scales on the inner surface of each thigh and crus.
Distribution
The striped mud turtle is found from the Florida Keys northward throughout peninsular Florida, and along the Atlantic Coastal Plain as far north as King and Queen County, Virginia (Lamb and Lovich, 1990).
Geographic Variation
No subspecies are currently recognized. Formerly, the mainland population and that from the Florida Keys were considered separate subspecies, but Iverson (1978b) showed that variation occurs throughout the range and that no populations are distinct.
Habitat
The striped mud turtle is most often found in quiet water with a soft bottom—swamps, sloughs, and ponds. It also frequents wet meadows, and enters brackish water.
Natural History
Wild females mature at 70-75 mm carapace length in 5-6 years (Iverson, 1979c); wild males contain mature sperm when 75 mm long (Einem, 1956). The female ovarian cycle is almost continuous, with only a short summer quiescence (Iverson, 1979c). Females can store sperm for long periods; a captive, isolated from males for at least 397 days, produced a fertile egg that subsequently hatched (Nijs and Navez, 1990).
Mating apparently occurs throughout the year, as Iverson (1977d) found oviducal eggs or fresh corpora lutea in every month. Its courtship has not been adequately described.
Nesting occurs from April to June. Nests are dug in sand or in piles of decaying vegetation. A clutch varies from one to five eggs, and possibly as many as three clutches may be laid each season.
Eggs are elliptical, whitish, and brittle shelled (22.8-31.8 x 13.6-19.3 mm; Iverson, 1977d). Incubation takes about 100-130 days, and embryos undergo a period of diapause (developmental arrest) in which early embryos developing under otherwise favorable environmental conditions await an additional environmental factor, particularly prolonged exposure to cool temperatures, that will terminate diapause and allow further development (Ewert and Wilson, 1996). The expression of diapause varies with nesting season and incubation temperature, with fewer embryos ceasing development in spring than in the fall, and fewer at warm temperatures than at moderately cool ones (Ewert and Wilson, 1996).
Hatchlings are black with yellow spots on each marginal. Their rough carapace (15-25 mm) has three weak keels, one beneath each stripe, and the yellow plastron is marked with a dark central blotch and dark-bordered seams. Plastral hinges are not functional until about the third month after hatching. The yellow head stripes are pronounced.
Kinosternon baurii is omnivorous. Natural foods include seeds of the cabbage palm (Sabal palmetto), juniper leaves, various algae, snails, insects, and dead fish. It is easily caught on a hook and line baited with liver, grasshoppers, worms, or dough. They also have some scavenging tendencies, and while on land may forage in cow dung, perhaps seeking insects.
IUCN Red List Status (1996)
Not listed.