Tetrabothrius shinni sp.nov. (Eucestoda) from Phalacrocorax atriceps bransfieldensis (Pelecaniformes) in Antarctica with comments on morphological variation, host–parasite biogeography, and evolution

Abstract

Tetrabothrius shinni sp.nov. is described from blue-eyed shags, Phalacrocorax atriceps bransfieldensis Murphy in the western Antarctic. Morphologically, T. shinni is most similar to Tetrabothrius phalacrocoracis Burt, 1977, the only other tetrabothriid known from the Phalacrocoracidae. Specimens of T. shinni are distinguished by a relatively small scolex, numerous testes, (35–61 in number), a large genital atrium (196–317 μm in diameter), a long male canal (86–160 μm in length) with a prominent distal sphincter, and the configuration of the genital atrium (massive ventrally directed male papilla with the aperture of the male canal located anterolaterally). The extreme intraspecific variation in some morphological characters evident in specimens of T. shinni suggests that a reevaluation of some Tetrabothrius spp. is required. The life cycle of T. shinni is thought to involve nototheniid fishes as second intermediate or paratenic hosts. The host and geographic distributions and a suite of unique characters shared by T. shinni and T. phalacrocoracis suggest that they are sister species in which cladogenesis during the Tertiary coincided with that of shags referred to the subgenera Leucocarbo and Stictocarbo.