The Treatise on Invertebrate Paleontology describes Euproopidae as "small forms with wedge-shaped cardiac lobe bordered by distinct axial furrows, abdominal shield with annulated axis bearing a high boss on last segment."

"[3] Unusually, Euproops may have been semiaquatic, due to being found in terrestrial substrates more often than aquatic ones, as well as the genal and ophthalmic spines of E. danae closely resembling lycopod twigs, alongside E. rotundatus resembling the arachnid Maiocercus.

[5] = Euproops kilmersdonensis Ambrose & Romano, 1972 according to Anderson (1994);[6] also E. gwenti and E. graigola, both from Upper Coal Measures strata in Wales, and E. darrahi from the Pennsylvanian Conemaugh Formation, Pennsylvania, USA according to Bicknell and Pates (2020).

In 2021, a specimen of E. danae was discovered with an exceptionally well-preserved brain and central nervous system (CNS).

It appears that the CNS of this (and perhaps other extinct horseshoe crabs) has remained essentially unchanged for some 300 m.y.