Manum, S. B.; Bose, M. N.; Sawyer, R. Y. T. (1991). "Clitellate cocoons in freshwater deposits since the Triassic". Zoologica Scripta. 20 (4): 347. doi:10.1111/j.1463-6409.1991.tb00300.x.
Tessler, Michael; de Carle, Danielle; Voiklis, Madeleine L.; Gresham, Olivia A.; Neumann, Johannes S.; Cios, Stanisław; Siddall, Mark E. (1 October 2018). "Worms that suck: Phylogenetic analysis of Hirudinea solidifies the position of Acanthobdellida and necessitates the dissolution of Rhynchobdellida". Molecular Phylogenetics and Evolution. 127: 129–134. doi:10.1016/j.ympev.2018.05.001.