<P> The main internal organs of these reptiles are the lungs, heart, stomach, liver, intestines, and the urinary bladder . A cloaca serves both excretory and reproductive functions . </P> <P> Some dimorphism exists between males and females . </P> <P> Red - eared slider young look practically identical regardless of their sex, making it difficult to determine their sex . However, there is another method to determine their sex, by inspecting the markings under their carapace . These markings will fade as the turtles age . It is much easier to distinguish the sex of adults, as the shells of mature males are smaller than those of females . Male red - eared sliders reach sexual maturity when their carapaces' diameters measure 10 cm (3.9 in) and females reach maturity when their carapaces measure 15 cm . Both male and females reach sexual maturity at five to six years . The male is normally smaller than the female, although this parameter is sometimes difficult to apply as individuals being compared could be of different ages . </P> <P> Males have longer claws on their front feet than the females; this helps them to hold on to a female during mating and is used during courtship displays . The male's tail is thicker and longer, it has a dark coloured retractable sexual organ known as their penis, inside the tail . Typically, the cloacal opening of the female is at or under the rear edge of the carapace, while the male's opening occurs beyond the edge of the carapace . The male's plastron is slightly concave, while that of the female is completely flat . The male's concave plastron also helps to stabilize the male on the female's carapace during mating . Older males can sometimes have a dark greyish - olive green melanistic coloration, with very subdued markings . The red stripe on the sides of the head may be difficult to see or be absent . The female's appearance is substantially the same throughout her life . </P>

How long does it take for red eared slider turtles to grow
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