The modern sea spider had started to diversify by the Jurassic https://phys.org/news/2023-08-modern-sea-spider-diversify-jurassic.html

New insights into the sea spider fauna (#Arthropoda, Pycnogonida) of La Voulte-sur-Rhône, France (#Jurassic, Callovian) https://onlinelibrary.wiley.com/doi/full/10.1002/spp2.1515

"#SeaSpiders (#Pycnogonida), are a group of #marine #animals that is overall very poorly studied. However, they are very interesting to understand the #evolution of #arthropods as they appeared relatively early in the #arthropod tree of life."