Appearance
''Platemys platycephala'' is a medium-sized turtle ranging from 14–18 cm in shell length. Females are slightly smaller on average with shorter tails. The carapace is elliptical and flattened with two raised portions forming a trough . The carapace is orange to yellow-brown and black in various amounts depending on subspecies. The plastron is dark brown or black in color while the bridge is yellow with a black bar across. The consistency of these bars also depends on subspecies. Face and neck patterns consist of orange or yellow-brown dorsal stripes and black ventral and lateral stripes. The head is small, triangular, smooth, and undivided. The neck has some conical tubercles- rounded projection and scales that protect against predator attack.''Platemys platycephala'' is a member of ''Pleurodira''- a suborder of turtle. These turtles withdraw their head into their shell by bending their necks sideways instead of straight back like ''Cryptodira''. The snout projects slightly and the irises are brown. Black limbs consist of large anterior scales while the tail is short and black. Intermediate webbing exists on both anterior and posterior limbs because this turtle moves in water and on land.
Naming
Two subspecies exist for the twist-necked turtle- ''Platemys platycephala platycephala'' and ''Platemys platycephala melanonota''. ''P. p. platycephala'' inhabits most of the central and eastern territory while ''P. p. melanonata'' inhabits the western territory . The chief distinction between these subspecies is the carapace coloration. ''P. p. melanonata'', , has an entirely dark brown or black top shell. These subspecies interbreed in Bolivia and various river drainages frequently forming variations in shell pattern.Distribution
The twist-necked turtle inhabits a large area throughout northern and central South America, from the southern Orinoco drainage in Venezuela to the Amazon basin in Brazil. However, ''Platemys platycephala'', does not inhabit large rivers but instead prefers shallow creeks and forest floors.Ernst surveyed the extensive geographical range of the twist-necked turtle and determined the presence of a dark subspecies in the western range of ''Platemys platycephala''. The author uses the "Quaternary forest refuge theory" to explain the existence of this subspecies. The theory is based on significant climatic changes occurring in and around the equator during the Quaternary period. During these climatic changes of glaciation the northern rainforests of South America received less rainfall and deteriorated then subsequently expanded during interglaciation. This change caused allopatric speciation to occur among many species and gave rise to a new subspecies- ''Platemys platycephala melanonota''.
Status
No direct threats are evident for ''Platemys platycephala'' because human consumption is inefficient due to the small size of the turtle. Additionally, this turtle does not perform well in captivity so the pet market is minimal but some amateurs do try,. France placed this species on its list of protected species for French Guiana and prohibits the capture of any specimens, for hunting, trading, etc. The IUCN Red List does not currently list this species. Additionally, the USGS reports a few twist-necked specimens were found on a southern Florida golf course but no impact is expected to occur.Habitat
The coloration and shape of the carapace, head, and feet help conceal this species of turtle from Amazon predator species. Naturally, twist-necked individuals prefer amphibian eggs and consume various insects, mollusks , amphibians, and some plant life through terrestrial and aquatic foraging. In captivity, specimens can flourish on reptile food, veggies, insects, worms and even fish. ''Platemys platycephala'' are likely to be found in shallow pools and can inhabit dry areas for long periods of time. Fretey states several individuals can even become heavily parasitized by leeches during the dormant dry season and suffer accordingly.Evolution
''Platemys platycephala'' young or hatchlings typically resemble parents except for brighter coloration. Twist-necked hatchlings measure around 4–6 cm in carapace length and about 20 g or 0.04 lbs. Mating typically occurs during the rainy season of the Amazon rainforest . Males follow females, mount from behind, then proceed to rub their chin barbels against the top of females’ head. Some authors also report violent biting and water expulsion from the males nostrils during copulation. Coupling has been observed on land or in water and usually occurs late in the afternoon or at night. Oviposition comes during the dry season when the female deposits a large, oval egg . Many herpetologists report females depositing another egg a couple of weeks later while some recreational collectors report multiple eggs at a time. Shallow indentations are made to deposit eggs and then lightly covered by sand and/or leaf litter.References:
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