The Echidna and Platypus
Monotremes belong to the Order 'Monotremata' and are a very specialised group of mammals. 'Monotreme' means 'one hole' and refers to the cloaca which is used for both reproduction and elimination of wastes.
Monotremes lay eggs with rubbery shells just like reptiles do. Also in common with reptiles are the legs which extend out from the body, giving the animal a waddling gait when on land. The body temperature is lower than that of most mammals. However the platypus has a wishbone (interclavicle) like a bird.
The scientific name of the short-beaked echidna is Tachyglossus (fast tongue) aculeatus (prickled). It is found in south-east New Guinea and throughout Australia wherever there are ants and termites. The echidna is also known as the spiny anteater.
The three living long-beaked echidna species belong to the Zaglossus genus and are endemic to New Guinea. They are hunted for food and are now rare.
Ornithorhynchus anatinus is the scientific name of the platypus. The Greek 'Platys' means 'flat or broad' and 'pous' means 'foot'. The platypus is the only venomous furred mammal. Hollow spurs on the inside of the ankles inject powerful venom which, while not lethal to humans, is extremely painful.
First descriptions of the platypus were treated with derision. A pelt sent back to the United Kingdom in 1798 was dismissed as a hoax. So bizarre was its appearance that the animal was first called by a number of descriptive names including duckbill, watermole and duckmole. It is often referred to now as the duck-billed platypus. It was not until 1884 that its egg-laying status was confirmed.
The platypus is semi-aquatic and forages along freshwater streams. They need earth banks for burrows. They lay leathery shelled eggs which are less than 2cm long. The female platypus incubates the eggs against her belly, holding them there with her tail. One to three babies are born. They are about 18mm long, blind and hairless. The platypus does not have teats but iron-rich milk oozes through the skin on the tummy and is sucked up by the babies.
The echidna lays a single egg which is carried in a pouch for about ten days. The pouch only develops during the breeding season. The baby stays in the pouch for around three months.
The platypus is covered with a double layer of fur. The top coat is denser than the fur on a polar bear and the undercoat is woolly. By contrast, the echidna is covered with sharp, cream coloured spines.
The bill of the platypus is actually an elongated 'snout'. For an animal regarded as primitive, this is one specialised instrument. Around 850,000 electrical and tactile receptors are contained in the snout. The platypus locates its prey by detecting electric fields generated by muscular contractions. By rocking its head from side to side (with the eyes, ears and nostrils shut), its electro-receptor system locates food which consists of various small aquatic creatures such as molluscs, worms and crustaceans.
Like the platypus, the echidna also has sensors in the snout but the system is not nearly as developed as it is in the platypus.
The long nose is stiff and hairless. The nose is 7 to 8cm long and is capable of breaking up logs and termite mounds. The mouth is at the end of the snout and on the underside. Echidnas are insectivorous. Prey is trapped with the long, sticky tongue then ground between the tongue and the hard pads of the mouth.
The echidna also has a hollow spur on the back leg but is unable to inject venom like the platypus.
Threats to the monotremes include loss of habitat, snakes, goannas, foxes, dingoes and birds of prey. The platypus faces entanglement with illegal fishing nets and drowning during flood periods. Loss of habitat is not such an issue for the echidna.
The monotremes are an interesting group. It is to be hoped that they will be around for many years to come.