Palaeoisopus,Palaeopantopus andPalaeothea,pycnogonid arthropods from the Lower Devonian Hunsriick Slate,West Germany

Palaeoisopus problematicus andPalaeopantopus maucheri are redescribed and found to be primitive pycnogonids belonging to extinct orders.Palaeoisopus is particularly primitive in retaining a long abdomen with a telson. It differs from other forms also in having flattened limbs indicating a swimming mode of life and in having the ocelli differently arranged.Palaeothea devonica nov. gen. et nov. spec. is a tiny pycnogonid, the only hitherto known fossil representative of the extant order Pantopoda, indicating that entirely modern forms were in existence already in the Early Devonian. A derivation of pycnogonids from early merostomes is regarded as likely.