Eurysilenium M. Sars, 1870

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 : 20

Genus Eurysilenium M. Sars, 1870

Diagnosis. Adult female ectosoma angular, bilaterally symmetrical, with inconspicuous genital swellings. Genital apertures transverse, slit-like, located ventrally on swellings at or near posterior margin of ectosoma. Stalk originating on flattened underside of ectosoma, distinctly in anterior half of body. Endosoma circular in crosssection and tapering gradually towards bulbous tip; typically looped around gut of host. Egg sacs curved, multiseriate. Adult male oblong, tapering posteriorly, indistinctly 6-segmented, comprising cephalothorax and 5 more-or-less well defined trunk somites; fourth trunk somite with paired, ventrally-directed lobate swellings; fifth (anal) somite bearing elongate caudal rami, hooked at tip. Single pair of stylet-like structures present in oral region.

Type species: Eurysilenium truncatum M. Sars, 1870 , by monotypy.

Remarks. There are currently five valid species in the genus Eurysilenium : E. truncatum , E. australis López- González, Bresciani & Conradi, 2006, E. fungosum Stock, 1996 , E. intermedium Stock, 1986 , and E. oblongum Hansen, 1887 . All species occur on polynoid worms. Only E. truncatum has been commonly reported from European waters, from southern Norway and Sweden, the Skagerrak and Kattegat ( Lützen 1964a, 1966, 1968), and Scotland ( O’Reilly et al. 2011). The known distribution of E. oblongum ranges from Labrador and Greenland in the west to the Kara Sea in the east ( Lützen 1964a). The remaining species are reported from New Caledonia ( E. intermedium ), Indonesia ( E. fungosum ), and Antarctica ( E. australis ) ( Stock 1986, 1996; López- González et al. 2006). The name E. antarcticum used by López-González et al. (2006: p. 258) is presumably a lapsus. The male of E. australis was described in detail using both light and scanning electron microscopy by López-González et al. (2006).