Five new species of Phoreiobothrium (Cestoda: Tetraphyllidea) are described from carcharhiniform sharks collected from a diversity of localities throughout the world. These are Phoreiobothrium perilocrocodilus n. sp. from Negaprion acutidens, Phoreiobothrium anticaporum n. sp. from Negaprion brevirostris, Phoreiobothrium lewinense n. sp. from Sphyrna lewini, Phoreiobothrium robertsoni n. sp. from Carcharhinus brachyurus, and Phoreiobothrium blissorum n. sp. from C. plumbeus, This brings the number of described species of Phoreiobothrium to 17. The new species from the lemon sharks, P. perilocrocodilus n. sp. and P. anticaporum n. sp., both possess more bothridial subloculi than do all species from hammerhead sharks, and fewer subloculi than do all species from sharks of Carcharhinus spp. Phoreiobothrium anticaporum n. sp. is unique among Phoreiobothrium species in that its genital pore is located in the extreme anterior portion of the proglottid. Phoreiobothrium lewinense n. sp. is unique in its possession of a combination of 8–11 subloculi and basal hook prongs that lack internal channels. Phoreiobothrium robertsoni n. sp. possesses 25–29 subloculi, triangular bothridia that flare posteriorly, and hooks that extend well beyond the middle of the bothridia. Phoreiobothrium blissorum n. sp. is most similar to Phoreiobothrium lasium in that it possesses rectangular bothridia with greater than 22 subloculi and long filitriches on its scolex. However, it differs from the latter species in that rather than articulating with one another, the bases of the medial and lateral hooks are widely separated; it also possesses 5–6 (vs.) 7–8 columns of testes. Phoreiobothrium lasium and Phoreiobothrium tiburonis are redescribed. The host associations of P. lasium are reevaluated and a neotype is designated for this species. The mature proglottid of P. tiburonis is described for the first time from voucher material collected from the type host and locality. These data suggest that the proglottid information provided in the original description, which was obtained from detached gravid proglottids, may have come from a tapeworm species other than P. tiburonis. All 7 species treated here in detail were examined with scanning electron microscopy; most were found to exhibit a microthrix pattern similar to that described previously for other members of the genus, e.g., Phoreiobothrium manirei. Bladelike spinitriches were present on the strobila, cephalic peduncle, and proximal bothridial surfaces, but were lacking from the distal bothridial surfaces. These spinitriches varied in length and density among species. Filitriches were present on all of these surfaces, but varied somewhat in length among species. Phoreiobothrium lewinense n. sp. is exceptional in that spinitriches were not seen on the proximal bothridial surfaces. A key to Phoreiobothrium species is provided. This work brings the number of carcharhinid shark species known to host this onchobothriid genus to 6, and the number of sphyrnid species to 5. Like many other onchobothriid tapeworms, species of Phoreiobothrium appear to exhibit oioxenous specificity for their hosts. Given this, and the fact that a total of 9 genera and 46 species of carcharhinid and sphyrnid sharks have yet to be examined for Phoreiobothrium, the diversity of the genus globally is likely to greatly exceed that described to date.

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