It is unknown whether the pain caused is a result of the associated edema around the wound or the venom has a component that acts directly on the pain receptors. While some muscle wastage has been observed in cases of envenomation in humans, it is likely due to the inability to use the limb while the effects of the venom persist. Unlike snake venom, there appears to be no necrotising component in the platypus's venom. Coagulating effects have been seen during experiments on laboratory animals, but this has not been observed consistently. The different chemicals in the venom have a range of effects from lowering blood pressure to causing pain and increasing blood flow around the wound. This venom appears to be related to that of several species that are not part of the platypus's evolutionary lineage, such as certain fish, reptiles, insectivores, and spiders, sea anemones, and starfish. This is the only known such example in mammalian systems. A unique feature of the venom is the presence of a D-amino acid. This appears to be an example of convergent evolution of venom genes from existing immune system genes ( defensins). The OvDLPs are related to, though distinct from, those involved in reptilian venom production. Those peptides that have been sequenced and identified fall into three categories: defensin-like peptides (OvDLPs), C-type natriuretic peptides (OvCNPs), and nerve growth factor (OvNGF). The crural gland produces a venom secretion containing at least nineteen peptides and some non-nitrogenous components. The spur normally lies flat against the limb but is raised when required. The spur is attached to a small bone that allows articulation the spur can move at a right angle to the limb allowing a greater range of attack than a fixed spur would allow. Female platypuses, in common with echidnas, have rudimentary spur buds that do not develop (dropping off before the end of their first year) and lack functional crural glands. The venom is produced in the crural glands of the male, which are kidney-shaped alveolar glands located in the upper thigh, and delivered through a spur, or calcar, on each hind limb. Rather than being a unique outlier, the platypus is the last demonstration of what was once a common mammalian characteristic, and it can be used as a model for non- therian mammals and their venom delivery and properties. Many archaic mammal groups possess similar tarsal spurs, so it is thought that, rather than having developed this characteristic uniquely, the platypus simply inherited this characteristic from its antecedents. While the venom's effects are described as extremely painful, it is not lethal to humans. The venom is made in venom glands that are connected to hollow spurs on their hind legs it is primarily made during the mating season. The platypus is one of the few living mammals to produce venom. The venom-delivering spur is found only on the male's hind limbs.
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