Palaeoisopus

[2] Sabroux et al. 2024 redescribed this genus alongside other Hunsrück pycnogonid fossils, by using both X-ray and RTI method they discover some new details, mostly those of the cephalic structures.The distal section (beyond the fourth segment/femur, which is unusually short for a pycnogonid) was flatten, lined with marginal setae and terminated by a robust, hook-like claw.In comparison, the second to fourth legs have 5 flatten distal segments that narrow towards the end and possess double rows of long ventral setae.Based on the purported large eyes, Bergström et al. 1980 suggest it rely on visual cues to find preys, with associated stalked crinoid (sea lily) as a possible target.[3] While some analysis placing them within Pantopoda (crown-group pycnogonids),[13] this result is questionable as they have low support value and based on outdated reconstrution of the fossil taxa.
Fossil showing the long, fully-extended front legs
Details of second to fourth legs
specimen associated with a crinoid
Haliestes
PreꞒScientific classificationAnimaliaArthropodaChelicerataPycnogonidaBroiliBinomial namefossilpycnogonidspeciesLower DevonianHunsrück SlateGermanyarthropodisopodcrustaceanColossendeisexoskeletontuberclescephalonproboscistelsoncheliceratesocelliappendagespincer-likecheliforespodomeresexual dimorphismPycnogonidaePhoxichilidiidaenektonicpredatorcrinoidHaliestesstem-groupancestralPentapantopuscrown-groupWikidataOpen Tree of LifePaleobiology Database