Swalla, B.J.; van der Land, J. (2024). Hemichordata World Database. Hormograptus defensor Öpik †. Accessed through: Marine Species Traits editorial board (2024) Marine Species Traits at: https://www.marinespecies.org/traits./aphia.php?p=taxdetails&id=579918 on 2024-10-11
Marine Species Traits editorial board (2024). Marine Species Traits. Hormograptus defensor Öpik †. Accessed at: https://www.marinespecies.org/traits/aphia.php?p=taxdetails&id=579918 on 2024-10-11