Cestodes of the order Onchoproteocephalidea II infecting cartilaginous fishes (Elasmobranchii) in South Africa

Abstract

South Africa is globally classified as the third most biodiverse country on Earth. However, the immense deficiency of taxonomic marine based initiatives, especially regarding parasitological research, within this region leaves the majority of this hidden biodiversity unrecognised and unexplored. What’s more, the current anthropogenic pressures placed on our marine ecosystems not only increase the threats posed on elasmobranch host survival, but increases the risk of the co-extinction of both host and parasites before their unique host-parasite system is discovered, and the benefits of their evolutionary relationship can be appreciated. Recognising the absence of taxonomic biodiversity research for cestode-elasmobranch systems in the ocean basins surrounding southern Africa, the present study was conducted to establish a foundation for future research within this field. By investigating the biodiversity of onchoproteocephalidean cestodes infecting elasmobranchs off the coast of South Africa, eight new onchoproteocephalidean species were discovered and described. These species are Acanthobothrium microhabentes Van Der Spuy, Smit et Schaeffner, 2020, A. microtenuis Van Der Spuy, Smit et Schaeffner, 2020, A. crassus Van Der Spuy, Smit et Schaeffner, 2020, A. dolichocollum Van Der Spuy, Smit et Schaeffner, 2020, A. umbungus Van Der Spuy, Smit et Schaeffner, 2022, A. usengozinius Van Der Spuy, Smit et Schaeffner, 2022, A. ulondolozus Van Der Spuy, Smit et Schaeffner, 2022 and Phoreiobothrium sp. A, seven of which have already been registered and published. The first four species of Acanthobothrium van Beneden, 1849, were reported to parasitise subsets of eight spotted skates, Raja straeleni Poll, whilst the following three species were reported to parasitise an endangered host species namely the white skate, Rostroraja alba (Lacépède). The last species, Phoreiobothrium sp. A, was reported from the spinner shark, Carcharhinus brevipinna (Valenciennes). This study was conducted by use of morphological methods (i.e. light microscopy and scanning electron microscopy). Furthermore, each species described was consequently distinguished from all other valid species worldwide, therefore ensuring the legitimacy of the new species. Although differing quite extensively from most congeners, five of the seven species of Acanthobothrium (A. microhabentes, A. microtenuis, A. crassus, A. dolichocollum and A. ulondolozus) seem to share a unique feature with merely 12 other species from the Indo-Pacific Ocean, suggesting that these might be each other’s closest relatives. Phoreiobothrium sp. A could possibly be the same species found by Jensen and Bullard (2010) off the coast of Mississippi, U.S.A. However, without a molecular phylogenetic analysis at this point these assumptions could not be proven. Moreover, since these eight species were recovered from a previously unexplored locality, and in two cases unexplored hosts, these results expand the geographical distribution, biodiversity and host associations of the order. Given the fact that three species were recovered from an endangered host, it is apparent to not only address the biodiversity of onchoproteocephalidean cestodes, but also to determine the specific, unique and evolutionary

host-parasite interrelationships. By recognising these cestodes as affiliate species, researchers could gain more knowledge of the ecological importance these species hold, which might give threatened elasmobranch species a better chance of survival. Hence, this study additionally highlights the necessity for the incorporation of novel and multisource approaches of interdisciplinary fields such as ecology, conservation science and ecotoxicology for future research.