(Le Sueur, 1827)
Spiny softshell turtle
Recognition
The round, leathery carapace (to 49.8 cm) has a rough, sandpaperlike surface. Conical projections or spines are present along the anterior edge of the shell. No preneural bone is present and only a single neural separates the anterior pair of costals. Seven or eight neurals and seven or eight pairs of costals present; if present, the 8th pair of costals is reduced, but the 7th pair meets at the midline. Carapacial bones are strongly pitted. The carapace is olive to tan, with a pattern of black ocelli or dark blotches and a dark marginal line. The plastron is immaculate white or yellow. It has well-developed callosities on the hyoplastra, hypoplastra, and xiphiplastra; poorly developed callosities occur on the epiplastra and entoplastron less frequently. The entoplastral angle is about 90°, and there is usually a suture between the hyo- and hypoplastra. The moderate-sized skull has a bony snout about as long as the greatest diameter of the orbit. The mandibular symphysis is shorter than the diameter of the orbit. There is no maxillary ridge and the maxillae touch above the premaxillae (not in contact in Apalone mutica). Head and limbs are olive to gray, with a pattern of dark spots and streaks. Two separate, dark-bordered, light stripes are found on each side of the head: one extending backward from the eye, the other backward from the angle of the jaw. The tubular snout has large nostrils, each of which contains a septal ridge; the lips are yellowish with dark spotting, and the jaws are sharp.
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 (12.7-21.6 cm) have long, thick tails with the vent near the tip, and retain the juvenile pattern of ocelli, spots, and lines. Adult females (16.5-49.8 cm) develop a mottled or blotched pattern.
Distribution
This species ranges from northwestern Vermont, southern Ontario, and Quebec to North Dakota and Montana and south to the Gulf Coast States and New Mexico. It also occurs in the Gila and lower Colorado rivers in California, Nevada, Arizona, and New Mexico and in the northern parts of Tamaulipas, Nuevo Léon, Coahuila, and eastern Chihuahua, Mexico. Individuals have also been taken from the lower Otay Reservoir and San Diego River in California, where introduced (Stebbins, 1985), and from the Red River of the North Basin along the Minnesota-North Dakota line. Apalone spinifera has also become established in Salem County, New Jersey.
Geographic Variation
Seven subspecies are recognized. The eastern spiny softshell turtle Apalone spinifera spinifera (Le Sueur, 1827) ranges east of the Mississippi River, from Vermont and extreme southeastern Canada west to Wisconsin and south to North Carolina, western Virginia, and Tennessee. It can be distinguished from the other subspecies by the presence of large black ocelli in combination with only one dark marginal line. A. s. hartwegi (Conant and Goin, 1948), the western spiny softshell turtle, ranges west of the Mississippi River, from Minnesota to Montana and south to northern Louisiana, Oklahoma, and northeastern New Mexico. It has uniform small dots and ocelli on the carapace and only one dark marginal line. A. s. aspera (Agassiz, 1857), the Gulf Coast spiny softshell turtle, occurs from southern North Carolina to southeastern Louisiana; its range includes the Florida Panhandle but not peninsular Florida. This race has more than one black line paralleling the rear margin of the carapace, and there is often a fusion of the postlabial and postocular stripes on each side of the head. The pallid spiny softshell turtle A. s. pallida (Webb, 1962) occurs west of the Mississippi in the upper Red River drainage and in rivers that drain into the Gulf of Mexico east of the Brazos River in Texas. It is pale and has white tubercles on the posterior half of the carapace; the tubercles gradually decrease in size anteriorly and are indistinct or absent on the anterior third of the carapace, and they are not surrounded by black ocelli. A. s. guadalupensis (Webb, 1962), the Guadalupe spiny softshell turtle, occurs in the Nueces and Guadalupe-San Antonio drainage systems of south-central Texas. It is dark and has white tubercles surrounded by narrow black ocelli on the anterior third of the carapace; some tubercles are as large as 3 mm in diameter. Small black dots are sometimes interspersed among the white tubercles. The Texas spiny softshell turtle A. s. emoryi (Agassiz, 1857) occurs in the Rio Grande drainage in Texas and New Mexico and the Colorado River drainages in Arizona, New Mexico, southwestern Chihuahua, central Coahuila, northern Nuevo Léon, and Tamaulipas. It has a pale rim on the carapace that is four or five times wider posteriorly than laterally. There is a dark, slightly curved line connecting the anterior margins of the orbits, and the postocular stripes usually are interrupted, leaving a pale blotch behind each eye. The black spiny softshell turtle A. s. ater (Webb and Legler, 1960) is restricted to permanent ponds in the Cuatro Ciénegas basin, Coahuila, Mexico. It is dark gray or brownish black with a gritty to smooth carapacial surface but no tubercles on the anterior rim. The rear carapacial margin is rugose and the edge ragged. Many black flecks occur on the plastron.
Originally described as a separate isolated species, ater is now considered only a subspecies of spinifera by Smith and Smith (1979). Drainage canals constructed in the Cuatro Ciénegas basin have allowed adjacent populations of A. s. emoryi to invade the range of ater, and Smith and Smith feel this has resulted in interbreeding, and that the turtles of the basin are losing their ater- like characters. However, a 1983 field trip by Kenneth Darnell, George Grall, and Anthony Wisnieski yielded several "pure" ater; thus a more thorough examination of the relationship between ater and emoryi is needed.
Habitat
Apalone spinifera inhabits a great variety of aquatic habitats, including marshy creeks, large swift-flowing rivers, bayous, oxbows, lakes, and impoundments. A soft bottom with some aquatic vegetation is essential, and sandbars and mud flats are preferred. Fallen trees with spreading underwater limbs are frequented. Individuals may migrate relatively long distances during the annual activity period; Vermont turtles overwintered about 3 km upriver from their summer feeding habitat (Graham and Graham, 1997).
Natural History
Mating takes place in April or May. Legler (1955) observed a captive male Apalone spinifera swim behind or above a female A. mutica and nip at the anterior part of her carapace. During these movements the posterior edge of her carapace was turned up slightly, whereas his was turned down. They frequently surfaced to breathe, and she occasionally followed him. When they settled to the bottom he crawled onto her carapace from the rear but did not clasp it with his feet.
June and July are the usual months of nesting, but the nesting season may begin in May and extend into August. The nests are flask shaped and extend to a depth of 10-25 cm.
The white, brittle eggs are spherical or nearly so and average about 28 (24-32) mm in diameter. Clutch size is 4 to 32 eggs, and probably more than one clutch is laid each year. Hatching occurs from late August to October.
The young resemble adult males in shape and color. The pale, olive to tan, rounded carapace has a well-marked pattern of small, dark ocelli or spots and a yellowish border set off by a black line. The granulation of its surface is pronounced, but the spines along the anterior edge are small and poorly developed. Hatchlings are 32.8-43.7 mm in carapace length (Graham and Graham, 1997). Bull and Vogt (1979) showed that sex determination in A. spinifera is independent of the incubation temperature; clutches they incubated at 25°C and 30.5°C both yielded approximately 1: 1 sex ratios.
A. spinifera is predominantly carnivorous; however, it consumes some plant material, possibly by accident. It eats crayfish, aquatic insects, mollusks, earthworms, fishes, tadpoles, and frogs.
This species is highly aquatic, spending most of its time in the water, either foraging, floating at the surface, or buried in the soft bottom with only the head and neck protruding. It buries itself by flipping silt over its back until it is entirely concealed. Often it lies buried under water shallow enough to allow the nostrils to reach the surface when the neck is extended, but it also burrows in deep water.
IUCN Red List Status (1996)
Apalone spinifera ater (listed as Apalone ater) is considered Critically endangered (A1ace, B1+2c); the other subspecies are not listed.