Tapeworms of the order Cyclophyllidea (the cyclophyllid cestodes) are the most important cestode parasites of humans and domesticated animals. All have multiple proglottid "segments", and all have four suckers on their scolices (heads), though some may have other structures, as well. Proglottids of this order have genital openings on one side (except in the Dilepididae, which have genital openings on both sides), and a compact yolk gland or vitellarium posterior to the ovary. Families include: