Hemianamorphic direct development has been observed in many arthropod groups, such as trilobites, megacheirans, basal crustaceans and basal myriapods. True direct development has on occasion been referred to as a trait unique to arachnids. There have been few studies on eurypterid ontogeny as there is a general lack of specimens in the fossil record that can confidently be stated to represent juveniles. It is possible that many eurypterid species thought to be distinct actually represent juvenile specimens of other species, with paleontologists rarely considering the influence of ontogeny when describing new species.