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. Like other mammals, monotremes have fur, nurse their young with milk, and are warm-blooded.The venom-delivering spur is found only on the male's hind limbs. In other mammals, the cloaca is divided into an anus and genitourinary passages. Monotremes, like all reptiles, also have a cloaca, a single opening through which feces, urine, and sperm or eggs pass. In monotremes, the eggs are fertilized internally, but are incubated and hatched outside the body. In other mammals, the young are conceived within the female's body and are born alive. For example, monotremes are the only egg-laying mammals. All three species in the order Monotremata are considered primitive, combining mammalian features with those of lower orders of vertebrates such as reptiles. There is only one species of platypus, Ornithorhynchus anatinus, which is comprised of four subspecies. The families are Tachyglossidae (the spiny anteaters or echidnas) and Ornithorhynchidae (the platypus). Gale Virtual Reference Library : Platypus The platypus is classified in the order Monotremata (meaning single hole), consisting of two families and three genera.
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