A New Genus and Two New Species of Aporhynchidae (Cestoda: Trypanorhyncha) from Catsharks (Carcharhiniformes: Scyliorhinidae) Off Taiwan

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 ,i n 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. The trypanorhynch family Aporhynchidae Poche, 1926 was established by Poche (1926) to accommodate Aporhynchus norve- gicus (Olsson, 1868) Nybelin, 1918, collected from Etmopterus spinax (L.) in the North Sea off Bergen, Norway. This species, the only member of its genus at that time, was unique among trypanorhynchs in lacking all elements of the rhyncheal apparatus. Since then, 3 additional species, also lacking the rhyncheal apparatus, have been described. These are Aporhynchus tasmanien- sis Beveridge, 1990, from Etmopterus baxteri Garrick off Tasmania, Pacific Ocean (see Beveridge, 1990), Aporhynchus menezesi Noever, Caira, Kuchta & Desjardins, 2010, and Aporhynchus pickeringae Noever, Caira, Kuchta & Desjardins, 2010, from Etmopterus spinax and Etmopterus pusillus (Lowe), respectively, from the waters surrounding the Azores Archipelago in the Atlantic Ocean (see Noever et al., 2010). Thus, all 4 species of Aporhynchus Nybelin, 1918 parasitize relatively deepwater-inhabiting sharks of the order Squaliformes, specifically species of Etmopterus Rafinesque. New collections of cestodes off Taiwan from a different order of deepwater-inhabiting sharks, in this case species of 2 genera of the carcharhiniform family Scyliorhinidae (catsharks), have resulted in the discovery of a second genus of trypanorhynchs that also lacks all elements of the rhyncheal apparatus. In combination, these sharks hosted 2 new species of this genus, considered here to represent a second genus of Aporhynchidae. This new genus and both new species are described below.