['Several independent meiofaunal lineages are suggested to have originated through progenesis, however, morphological support for this heterochronous process is still lacking. Progenesis is defined as an arrest of somatic development (synchronously in various organ systems) due to early maturation, resulting in adults resembling larvae or juveniles of the ancestors. Accordingly, we established a detailed neuromuscular developmental atlas of two closely related Dinophilidae using immunohistochemistry and CLSM. This allows us to test for progenesis, questioning whether i) the adult smaller, dimorphic ', 'Both species form longitudinal muscle bundles first, followed by circular muscles, creating a grid of body wall musculature, which is the densest in adult '] Does comparison of neuromuscular development in two dinophilid species ( Annelida ) suggest progenetic origin?