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During a helminthological study of waterfowl in China,a new species (Cloacotaenia cygnimorbus sp.nov.) of hymenolepidid cestodes (tapeworm) was found in the small intestine of whooper swan (Cygnus cygnus,Linnaeus,1758).The rudimentary rostellum and four unarmed muscular suckers,proglottids with distinct craspedote and three spherical testes were coincident with the characters of Cloacotaenia or Hymenolepis,but phylogenetic analysis of 28S rRNA and coxl gene revealed that the new species is Cloacotaenia rather than Hymenolepis.Its morphology was also clearly differentiated from C.megalops in the arrangement of its testes in a triangle instead of in line and the cirrus unarmed rather than spined.Compared with C.megalops,the new species has more elongated neck,much larger mature proglottids and much smaller testes,cirrus sac,ovary,vitellarium and uterine proglottid.In addition,it infected the host intestine not the cloacae.Phylogenetic analysis of cox1 gene of the new species shows that it had a level of sequence variation (10.52-23.06％) with the sequences of C.megalops.The considerable morphological and molecular differences between those two parasites support C.cygnimorbus sp.nov.as a new species.