The Archostemata are the smallest suborder of beetles, consisting of fewer than 50 known species organized into five families. They are an ancient lineage with a number of primitive characteristics. They are similar in morphology to the first beetles, which appear in the fossil record about 250 million years ago. Antennae may be thread-shaped (filiform) or like a string of beads (or moniliform). This suborder also contains the only paedogenic beetles, Micromalthus debilis.