Stylonurina is one of two suborders of eurypterids, a group of extinct arthropods commonly known as "sea scorpions". Members of the suborder are collectively and informally known as "stylonurine eurypterids" or "stylonurines". They are known from deposits primarily in Europe and North America, but also in Siberia.

Compared to the other suborder, Eurypterina, the stylonurines were comparatively rare and retained their posterior prosomal appendages for walking. Despite their rarity, the stylonurines have the longest temporal range of the two suborders. The suborder contains some of the oldest known eurypterids, such as Brachyopterus, from the Middle Ordovician as well as the youngest known eurypterids, from the Late Permian. They remained rare throughout the Ordovician and Silurian, though the radiation of the mycteropoids (a group of large sweep-feeding forms) in the Late Devonian and Carboniferous is the last major radiation of the eurypterids before their extinction in the Permian. The extinction of the latest definitive species, Campylocephalus permianus, occurred either during the late Early Permian-early Middle Permian (Kungurian-Roadian stages) or the Late Permian, while the other possible Late Permian taxon, Woodwardopterus freemanorum, may instead represent a true scorpion.

Though the Eurypterina contains several famous giant eurypterids such as Pterygotus and Jaekelopterus, the Stylonurina gave rise to large forms as well, several larger than a metre in length. The largest known stylonurine was Hibbertopterus scouleri, with a potential length of almost 2 metres (6 ft 7 in).

Stylonurina contains a wide variety of different genera and species. They are all unified by possessing transverse sutures on the ventral plates and lacking a modified podomere 7a on appendage VI.

The suborder is divided into four major superfamilies; the Rhenopteroidea, Stylonuroidea, Kokomopteroidea and Mycteropoidea. The most primitive of these, the Rhenopteroidea, includes several previously enigmatic genera, such as Brachyopterus, Kiaeropterus and Rhenopterus, all united by a rounded posterior margin to the metastoma and the prosomal appendage III bearing single fixed spines. Brachyopterus is also one of the oldest known genera of eurypterid, being from the Middle Ordovician.

The least well-supported group is the Stylonuroidea, containing the problematic genera Stylonurus and Stylonurella, partly due to the incomplete nature of the only known specimen of Stylonurus powriei which does not preserve the anterior prosomal appendages or any details of the ventral structures. Specimens of other members of the group are similarly incomplete, with Stylonurella spinipes not preserving the metastoma or pretelson and telson and Pagea sturrocki not preserving any dorsal structures.

The superfamilies Mycteropoidea and Kokomopteroidea are sister groups, united by a median ridge on the carapace between the lateral eyes and a distal thickening to the podomeres of the prosomal appendages. Though sometimes classified as an order separate from Eurypterida itself, the hibbertopterids are clearly recovered as stylonurine eurypterids in the latest analyses of the group.

Strategies for sweep-feeding (raking through the substrate in search of prey) evolved independently in two of the four stylonurine superfamilies, the Stylonuroidea and the Mycteropoidea. In both superfamilies, the adaptations to this lifestyle involves modifications to the spines on their anterior prosomal appendages for raking through the substrate of their habitats. Rhenopteroids, kokomopterids and parastylonurids retained primitive prosomal appendages II-IV that were unsuited for sweep-feeding and likely adopted scavenging, whilst the hardieopterids may have been benthic bottomdwellers living partially buried in the substrate.