ECHIDNA or SPINY ANT-EATER (Echidna aculeata), one of the Monotremata (q.v.) the lowest subclass of Mammalia. It is a native of Australia, burrowing in sand, or hiding in rock crevices. In size and appearance it resembles a hedgehog, its upper surface being covered over with strong spines directed back wards and inwards, so as to cross each other on the middle line. The tail is very small. It has a long tubular snout with a small mouth; its tongue is long and slender, lubricated with a viscous secretion, by means of which it seizes the insects on which it feeds. It has no teeth. Its legs are short and strong and form powerful burrowing organs. The male echidna has its heel provided with a sharp hollow spur, connected with a gland. It is a nocturnal animal. When attacked it seeks to escape either by rolling itself into a ball of by burrowing rapidly into the sand. Two eggs are laid and these are carried, as are the young at an early stage, in an abdominal pouch, into which open the mammary glands. The echidnas are restless in confinement and constantly endeavour to effect their escape by burrowing.
There are two varieties, the Port Moresby echidna and the hairy echidna. The latter is found in south-eastern New Guinea, Australia, and Tasmania. In all the spines are mixed with hair ; in the Tasmanian race they are nearly hidden by the long harsh fur. Of the three-clawed echidnas (Proechidna) confined to New Guinea there are two species.