Cutler, Edward B.; Cutler, Norma J. (1985). A revision of the genera Sipunculus and Xenosiphon (Sipuncula). Zoological Journal of the Linnean Society. 85: 219-246.
A critical analysis of historically used characters, based on a large series of specimens, is presented. Based on a comparative morphological analysis of type specimens, the 19 species of Sipunculus and four of Xenosiphon are reviewed. The genera and subgenera are redefined so that, after appropriate revisions arc made, Sipunculus (Sipunculus) has eight, Sipunculus (Contraporus) new subgenus has two, and Xenosiphon has only one remaining valid species. A zoogeographical note and a key to the species are included.
