Plumulites tafennaensis

Plumulites belongs to the Machaeridian group, a group of annelids or segmented but armored worms, known from the Early Ordovician to the Carboniferous.
Plumulites had strong walking limbs, arranged like bristles, and a set of mineralized plates on the back “armor plates”. These plates were rigid, but could move relative to each other, providing the animal with protective armor very similar to the flexible metal armor invented by humans 450 million years later. Possibly, this characteristic helped him survive. These articulated specimens reach around several centimeters in length, and are very rare, hence the limited degree of study since their description in 1857.
The group had been variously assigned to echinoderms, annelids, barnacles and mollusks, before the discovery of a fossil preserving soft tissue allowing a firm classification into annelids, in 2008. This affinity with annelids came as a surprise, as it is the only case of this group developing calcitic armor.