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The white skate, Rostroraja alba (Lacépède), is listed as an endangered species, the second-highest category before being declared extinct in the wild, in the International Union for Conservation of Nature's (IUCN) Red List of Threatened Species. This species is heavily affected by anthropogenic impacts such as capture induced stress by overfishing and by-catch, habitat degradation and pollution that caused a drastic decline in populations in recent years. As part of a larger study on elasmobranch affiliates in southern Africa, two specimens of R. alba were screened. Three species of the tapeworm genus Acanthobothrium van Beneden, 1849 (Cestoda: Onchoproteocephalidea) were discovered. Application of Ghoshroy and Caira's classification system facilitated the differentiation of congeners through a combination of specific morphological characteristics. As a consequence, three species new to science are described herein, namely Acanthobothrium umbungus n. sp., Acanthobothrium usengozinius n. sp., and Acanthobothrium ulondolozus n. sp. In light of these new discoveries from an endangered host, it is apparent to address the conservation status of its affiliate species, that co-evolved with their elasmobranch hosts for millions of years, thereby creating unique and intimate host-parasite interrelationships. Currently, altering environmental conditions caused by anthropogenic pressures have direct impacts on this host-parasite system with increasing risks of extinction. As merely 9% of elasmobranchs in South African waters have been examined for endohelminths and other affiliate taxa, extensive studies on these organisms and their hosts implementing multisource approaches are needed. This will provide a better understanding on the intimate nature of host-parasite systems that may lead to new prospects in conservation science and the preservation of threatened host species, such as R. alba , together with their unique fauna of affiliate species.

The extreme sparsity of collection efforts in many parts of the word, including southern Africa, leaves a vast hidden diversity of marine cestode species, such as species of Phoreiobothrium. The investigation of a common South African coastal-pelagic species, the spinner shark Carcharhinus brevipinna (Valenciennes) resulted in the discovery of a new species of Phoreiobothrium Linton, 1889. Phoreiobothrium martini n. sp. is undoubtedly different from all other congeners in several morphological characteristics, however, it is most easily distinguished from other species by the size of its hooks. Furthermore, this species is peculiar in the sense of its microthrix pattern. It only possesses filitriches on its proximal bothridial surface. Additionally, P. martini n. sp. also displays a scarcity of gladiate spinitriches on its cephalic peduncle. This has not been recorded in any other congener within this genus and could resemble a new, generic characteristic. The addition of P. martini n. sp. increases the total number of valid species of Phoreiobothrium to 18 worldwide. Furthermore, P. martini n. sp. marks the description of representatives of only the second onchoproteocephalidean genus from southern Africa, therefore expanding the generic biogeographical representation and introducing new host associations. Apart from the description of this new species of cestode, the discovery of P. martini n. sp. as well as additional species of Phoreiobothrium is beneficial regarding future ecological investigations. With the high degree of host-specificity found amongst species of Phoreiobothrium, species such as P. martini n. sp. could be used as sentinel species for the accurate identification, separation and diagnosis of commonly misidentified shark species, such as C. brevipinna and C. limbatus (Valenciennes).

The extreme sparsity of collection efforts in many parts of the word, including southern Africa, leaves a vast hidden diversity of marine cestode species, such as species of Phoreiobothrium. The investigation of a common South African coastal-pelagic species, the spinner shark Carcharhinus brevipinna (Valenciennes) resulted in the discovery of a new species of Phoreiobothrium Linton, 1889. Phoreiobothrium martini n. sp. is undoubtedly different from all other congeners in several morphological characteristics, however, it is most easily distinguished from other species by the size of its hooks.Furthermore, this species is peculiar in the sense of its microthrix pattern. It only possesses litriches on its proximal bothridial surface. Additionally, P. martini n. sp. also displays a scarcity of gladiate spinitriches on its cephalic peduncle. This has not been recorded in any other congener within this genus and could resemble a new, generic characteristic. The addition of P. martini n. sp. increases the total number of valid species of Phoreiobothrium to 18 worldwide. Furthermore, P. martini n. sp. marks the description of representatives of only the second onchoproteocephalidean genus from southern Africa, therefore expanding the generic biogeographical representation and introducing new host associations.Apart from the description of this new species of cestode, the discovery of P. martini n. sp. as well as additional species of Phoreiobothrium is bene cial regarding future ecological investigations. With the high degree of host-speci city found amongst species of Phoreiobothrium, species such as P. martini n. sp. could be used as sentinel species for the accurate identi cation, separation and diagnosis of commonly misidenti ed shark species, such as C. brevipinna and C. limbatus (Valenciennes).host species (Caira et al. 2017; Alijanpour Darvishsi & Haseli 2019). Species of Phoreiobothrium are known to explicitly parasitise sharks, with the majority (11/17) infecting sharks of the family Carcharhinidae, whilst the remainder (6/17) infect sharks from the family Sphyrnidae Caira et al. 2021). Information regarding the life-cycles of cestodes belonging to this genus is however still insu cient (Caira & Reyda 2005;Jensen 2005). This is due to the fact that these cestodes often mature in their relevant elasmobranch hosts species (Jensen & Bullard 2010). Larval Phoreiobothrium found to parasitise the intermediate hosts, such as teleost shes, do not resemble the morphology of their adult stages (Caira & Reyda 2005;Jensen & Bullard 2010). Consequently, larval cestodes of this genus cannot accurately be assigned to species-level without the aid of molecular sequence data.Given that the de nitive hosts of the 17 currently accepted species of Phoreiobothrium only represent 21% (11/52) of recognised carcharhinid and 66% (6/9) of sphyrnid shark species (Froese & Pauly 2021;Caira et al. 2021), several species await scienti c discovery. There are also sparse collection efforts of speci c hosts for parasitic research in many part...

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