Xenocoelomidae Bresciani & Lützen, 1966

Boxshall, Geoff A., O’Reilly, Myles, Sikorski, Andrey & Summerfield, Rebecca, 2019, Mesoparasitic copepods (Copepoda: Cyclopoida) associated with polychaete worms in European seas, Zootaxa 4579 (1), pp. 1-69 : 60

Family Xenocoelomidae Bresciani & Lützen, 1966

This family currently comprises three species placed in two highly transformed genera: Xenocoeloma Caullery & Mesnil, 1915 and Aphanodomus C.B. Wilson, 1924 . The latter is virtually endoparasitic, maintaining only a single opening through the host’s body wall through which paired egg sacs are extruded, while Xenocoeloma appears to be attached completely externally to the host. Caullery & Mesnil (1919) considered that the body of Xenocoeloma is almost entirely covered by the ectoderm of the host, but subsequent studies by Bocquet et al. (1968) concluded that the outer membrane covering the body is the modified integument of the copepod and is not of host origin. Both genera possess a posteriorly-located common genital atrium, within which both egg sacs originate. Both genera also exhibit an unusual reproductive strategy, cryptogonochorism, in which the mature adult male is effectively reduced to a testis which is housed within the receptaculum masculinum of the female ( Bresciani & Lützen 1972, 1974). The life cycle consists of a dispersal phase, the nauplius, followed by the infective copepodid larva which penetrates the polychaete host, and a parasitic phase. The developmental stages within the host have been summarised by Bresciani & Lützen (1974, fig. 42).