ἔχιδνα

Greek ekhidna meant a viper or serpent — specifically, the mythological creature Echidna: half beautiful woman, half serpent, who lived in a cave beneath the earth and was mother to the Hydra, the Chimera, Cerberus, and other monsters of Greek myth. Ekhidna's name came from ekhis (viper), from a root meaning sharp-pointed.

George Shaw, who named the platypus in 1799, also described the echidna, naming it Echidna in 1792 (later revised to Tachyglossus). The choice was probably for the animal's spines — the sharp-pointed quills resembling a viper's fangs or the mythological monster's threatening quality. The echidna's spines, its reclusive nature, and its underground habits (it burrows) made the snake-monster reference apt.

The echidna is the other monotreme — the only mammals other than platypuses that lay eggs. Unlike the platypus, the echidna has a pouch: the female lays a single leathery egg directly into a pouch, where it hatches after 10 days. The baby echidna, called a puggle, stays in the pouch until its spines emerge, whereupon the mother deposits it in a burrow and returns to nurse it.

The short-beaked echidna (Tachyglossus aculeatus) is among the most widely distributed mammals in Australia and New Guinea. Despite this success, it is poorly understood — echidnas are extremely difficult to study because they enter a state of torpor that is neither true hibernation nor wakefulness. Their brain structure, including an enormous cortex relative to body size, suggests high cognitive ability that their behavior has not yet explained.