New collections of cestodes from the spiral intestines of catsharks (Carcharhiniformes: Scyliorhinidae) off Taiwan have led to the discovery of a new genus and 2 new species of trypanorhynchs. These taxa are relatively unique among trypanorhynchs in their lack of all elements of the rhyncheal apparatus. The new genus, Nakayacestus n. gen., is considered to belong with Aporhynchus in the Aporhynchidae. In addition to lacking the rhyncheal apparatus, these 2 genera share circum-medullary vitelline follicles, post-ovarian testes, and complex terminal genitalia consisting of accessory, external, and internal seminal vesicles. The 2 genera differ conspicuously in spinithrix configuration; whereas both species of Nakayacestus n. gen. bear scolex spinitriches that are bifid, trifid, or pectinate, species of Aporhynchus either lack scolex spinitriches entirely or possess spathulate spinitriches. The configuration of the bothria of the 2 genera also differ conspicuously. Whereas the bothria of Aporhynchus are sessile and generally do not extend beyond the lateral margins of the cephalic peduncle, those of Nakayacestus bear only a tenuous connection with the scolex proper, being conspicuously free both anteriorly and posteriorly and extending conspicuously beyond the cephalic peduncle. Futhermore, the boundary between the scolex and the strobila of members of the new genus is clearly delineated, whereas this distinction is ill-defined in species of Aporhynchus. Nakayacestus takahashii n. sp., the type of the new genus, was collected from the Broadmouth catshark, Apristurus macrostomus, and differs from Nakayacestus tanyderus n. sp., collected from the Blacktip sawtail catshark, Galeus sauteri, in being shorter, bearing a longer pedunculus scolecis, an ovary that is more posterior in the proglottid, and fewer post-ovarian testes. Furthermore, the 2 new species differ conspicuously from one another in the configuration of their scolex spinitriches.

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