The sense of smell is acute. The tail is vestigial. The braincase of the skull is large and rounded, and the brain is relatively large, with convoluted cerebral hemispheres. The rostrum is long, tubular, and tapering, and the lower jaw is represented by two slender bones. The mouth is small.
Teeth are absent throughout life.
The posterior part of the long, sticky tongue has horny serrations that work against hard ridges on the palate for grinding food. In other aspects, the blood of echidnas resembles that of other mammals. Echidnas are powerful diggers. An individual, in a horizontal position, can burrow straight down with remarkable speed. Shelters include hollow logs, cavities under roots or rocks, and burrows.