| Pelusios | |
|---|---|
 | |
| Pelusios castaneus | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Testudines |
| Suborder: | Pleurodira |
| Family: | Pelomedusidae |
| Genus: | Pelusios Wagler, 1830[1][2] |
| Species | |
See text | |
| Synonyms[1][2] | |
SternothaerusBell, 1825 | |
Pelusios is agenus of Africanside-necked turtles. With 17 describedspecies, it is one of the most diverse genera of theturtle order (Testudines).
The scientific namePelusios is derived from theGreek word pēlos, which means "mud" or "clay",[3] and this is reflected by the turtles living in streams and rivers with a muddy bottom.
Common names for the genusPelusios includehinged terrapins,[4]African mud turtles, andmud terrapins.
Several species have been described, with probably numerous undescribed species. Thetaxonomy of the genus is very confused, as these species show many local variations. Certain species, in isolated areas or with reduced populations, need to be observed as they face a distinct extinction possibility given the significant number collected by native people.
They are found throughoutSub-Saharan Africa,Madagascar,São Tomé, and theSeychelles islands. They have also been introduced on the islands of theLesser Antilles.
The African mud turtles range from being small in size, only 12 cm (4.7 in) carapace length for adultPelusios nanus, to moderately large, 46 cm (18 in) for adultPelusios sinuatus, while the large majority of species fall between 20 and 30 cm (7.9 and 11.8 in) carapace length.[5] Thecarapaces are oblong, moderately high-domed, and theplastrons are large and hinged which is what distinguishes them from thePelomedusa.[5][6] The plastron contains a mesoplastron and also well-developed plastral buttresses that articulate with thecostals on each side of the carapace.[5] The carapace has 11 pairs of sutured peripherals around its margin and a neck withoutcostiform processes.[5] The jaw closure articulates on apterygoidtrochlear surface which lacks a synovial capsule but instead contains a saclike duct full of fluid from the mouth cavity.[5] The head shape is wide and flat, with a seemingly "smiling" face created by the jaw closure.[6] The skull lacks the epipterygoid bone (bone above the pterygoid extending toparietal bone) and parietal-squamosal contact but possesses an internalcarotid canal and strongpostorbital-squamosal contact.[5]
The mud terrapins are eithersemiaquatic or fullyaquatic and typically walk on the floor of slow-moving waters. They are most often observed in lakes, swamps or marshes but occasionally witnessed inephemeral waterways.[5] They are predominantlycarnivorous, eating a variety ofarthropods, worms, or other small animals found by way offoraging the bottom of their aquatic habitats.[5] They do not undergo prolongedestivation orhibernation in the dried mud during dry season; instead, they need to find a wet or humid place to survive.[6]Pelusios generally produce small to modestclutches of 6 to 18eggs, depending upon female size.[5][7] Egg deposition occurs in the more equitable season of the year, with known incubation periods ranging from 8–10 weeks.[5] The reportedkaryotype is 2N = 34 with 22 macrochromosomes and 12microchromosomes.[8] The southern group of the genusPelomedusa is shown to beparaphyletically similar toPelusios throughmitochondrial DNA analyses.[2][9] From fossil evidence, it is suggested that thegenera diverged in, or before the lower Miocene era.[9]
The species in the genusPelusios can be divided into two groups based on shell morphology. The "adansonii group" (also known as the "gabonensis group" or the "adansonii-gabonensis group") includesP. adansonii,P. broadleyi,P. gabonensis,P. marani, andP. nanus. Species in the "adansonii group" are characterized by short abdominalscutes relative to the elongate anterior plastral lobe, as well as a short bridge between the carapace and the plastron.[2] All of the remaining species are characterized by relatively longer abdominal scutes and a longer bridge between the carapace and plastron and are referred to as the "subniger group".[2][8] Species in the "subniger group" exhibit greater mobility of the plastral front lobe than those belonging to the "adansonii group".
Based on field surveys, a 50% decrease has been observed in the Seychelles terrapins, which include variousPelusios species.[13] Seychelles is considered a hotspot forbiodiversity, as it is one of the most threatened reservoirs of plant life and animal life, as well as one of the richest environments.[14] The species are endangered due to threat ofdrainage,predation, andinvasion by alien flora, combined with a shrunken living area.[13][14] Mosthabitat destruction is from human population expansion, specifically in thegranitic islands due to increased development pressures.[14] Hope for reversal of this trend is evidenced by the rapid population recovery ofPelusios subniger parietalis onFrégate Island after habitat improvement.[13]Globalclimate change has recently been recognized as one of the largest threats to biodiversity.[15] This climate change has the ability to change species survival by causing changes in ecosystem structures,[14] yet the effect is heightened inendemic species.[15] Several reviews undertaken for the study of potentialeffects of global warming on biodiversity have provided evidence for Africa being the most vulnerable of all continents.[16] Climate change is likely to be devastating for many species confined to small islands such as Seychelles.[14] Endemic species such asPelusios could suffer the worst impact of climate change because of their restricted range and narrow ecological requirements.
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