Gould-Somero, M. (1975). Echiura, in: Giese, A.C. et al. (Ed.) Reproduction of marine invertebrates: 3. Annelids and Echiurans. pp. 277-311
In: Giese, A.C.; Pearse, J.S. (Ed.) (1975). Reproduction of marine invertebrates: III. Annelids and Echiurans. Academic Press: New York. ISBN 0-12-282503-9. XII, 343 pp. https://dx.doi.org/10.1016/B978-0-12-282503-3.X5001-9, meer
