Aquilonifer

Aquilonifer spinosus is an extinct species of arthropod from the Silurian period. It is known from a single fossil specimen found in the Wenlock Series Lagerstätte of Herefordshire, England, in rocks about 430 million years old. The 1 cm long specimen is a stem-group mandibulate, not directly related to any living species. The many-legged, eyeless adult has ten unusual tethered appendages, interpreted as juveniles attached to the parent, in a unique form and previously unknown brooding behaviour.

Studies in 2018 and 2022 recovered Aquilonifer as a possible close relative of Pycnogonida and Marrellomorpha, suggesting that the latter is a paraphyletic group, but this result was considered unexpected by the authors of both studies.