Machaeridia is an extinct group of armoured, segmented annelid worms, known from the Early Ordovician (Late Tremadoc) to Carboniferous.

These are tiny, and usually found disarticulated: articulated specimens reach about a centimeter in length, and are incredibly rare – hence the limited degree of study since their description in 1857.

[4] The Plumulitid machaeridians would have moved across the surface of the sea floor using parapodia, whereas the fully armoured Turrelepids and Lepidocoelids burrowed in a peristaltic fashion reminiscent of their evolutionary cousins, the earthworms.

[8] In 2008, the discovery of a fossil preserving soft tissue (including chaetae and parapodia) established an annelid affinity.

In an accompanying commentary, Jean-Bernard Caron suggested that machaeridians must be a stem group based on number of specialised features.

He also suggested that machaeridians might be polyphyletic, but machaerdians are a well defined group with a number of shared characters and morphological gradations among all three families.