Black Knob Sawback
Graptemys nigrinoda
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Identification
The black-knobbed map turtle can be distinguished from other map turtles by the black knobs at the end of the spokes on their keels. There are two subspecies of the species Graptemys nigrinoda. These include the northern black knobbed map turtle (G. n. nigrinoda) and the southern black knobbed map turtle (G. n. delticola). While the southern black knobbed map turtles have markings on their plastrons, northern black knobbed map turtles lack such markers. The carapace of G. nigrinoda is slightly domed with the first four vertebrae possessing backward-projecting, knob-like processes, which are black in color. The second and third processes are more dominant in size compared to the first and fourth. With aging females, the knobs are reduced to small swellings. The carapace is dark olive-brown in color. Within each pleural, or "plate", of the shell are yellow-green circular rings which are outlined in black. Hatchlings are similar in color to adults, but the colors tend to be more vibrant and contrasting. The knob-like processes are compressed laterally. The head is small, and is dark brown with yellow stripes, with yellow crescents behind the eye facing towards the posterior end of the turtle. These stripes continue on the legs of the turtle also, with the underside of the leg being lighter than the dorsal surface.
Range
The black-knobbed map turtle is endemic to the southeastern United States. In Alabama, they are found in the Mobile Bay drainage. In Mississippi, they are found in the Tombigbee River system and in the Black Warrior River as far north as Jefferson County, Alabama. They are only able to survive in fresh water, thus they are only found within freshwater river systems.
Diet
Feed this turtle a high-protein diet. Some of the best commercial turtle foods include Mazuri Aquatic Turtle Diet, and Tetra Reptomin Floating Food Sticks. Supplement the commercial diet with animal protein such as shrimp, earthworms, crayfish, feeder fish, mealworms, bloodworms, crickets, and other insects.
Notes
Sexual dimorphism is evident in this species. Females are roughly twice the size of males. Also, females' carapaces tend to be higher than those of males, though the males have longer tails than the females. Sizes (carapace lengths) have been recorded as ranging from 7.6 to 10.2 cm (3–4 in) in males and 10.2–19.1 cm (4–7.5 in) in females. The black knobbed map turtle is a display pet and shouldn't be often handled unless it's necessary. Specimens are generally skittish and will shy away from human contact. As they come to associate you, the keeper, with food, they may rush towards you when you approach the enclosure. Map turtles of all kinds are avid baskers, spending many hours during the day in the sun. When with other turtles, they also are very communal, sharing space and using each other for predator watching, increasing the odds of surviving an attack. These turtles are extremely wary. If one dives, they all dive. As small turtles, the black knobbed map turtle does not require too much space. An adult male needs about a 25 to 30-gallon tank; while the larger adult females need a 75-gallon aquarium. A larger aquarium is always preferable as map turtles are lively swimmers. Also, two or more map turtles can be housed in an aquarium. Similarly, you can house them with cooters, sliders, and other North American turtles.
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