What is "machaeridian"

n. A fossil form of segmented (annelid) worm, of the class ''Machaeridia'', that had a scaly armour of mineralised plates

Machaeridia is an extinct group of armoured, segmented annelid worms, known from the Early Ordovician (Late Tremadoc) to Carboniferous. The group consist of three distinct families: the plumulitids, turrilepadids and lepidocoleids.